nurbs modeling 1

NURBSModeling

Using Maya: Modeling iii

NURBS Modeling

1 NURBS Modeling 1Modeling basics 1

Using construction history 2

Using curves to build surfaces 4

Creating objects using NURBS primitives 5

Creating surfaces 5

Editing curves and surfaces 7

Creating locators and measuring distances 10

Using the Show Manipulator Tool 11

Selecting an item’s history node 12

Changing a curve’s parameter range 14

Editing subCurves in the Attribute Editor 19

Editing parameters with manipulators 21

Editing attributes with manipulators 22

Using the Attribute Editor 22

Accessing the Attribute Editor 22

Using axes and pivot points 26

What are pivot points? 26

What is an axis? 29

Creating locators 31

Using Measure tools 33

Using distance measures 33

Displaying parameter values 38

Measuring arc lengths 41

NURBS modeling tips and tricks 45

Tools and actions 45

Workflow tips 45

Modeling tips 47

iv Using Maya: Modeling

NURBS Modeling in MayaContents

Using commands 49

Organizational tips 50

Special scripts 51

2 Introduction to Curves 53Curve basics 53

Creating the perfect curve 54

Which curve creation method should you use? 54

What are CV curves? 57

What are edit point curves? 58

Deleting curve segments 58

Deleting CVs on a surface 59

3 Creating curves 61Creating curves with CVs 61

Changing the CV curve shape 63

Setting CV Curve Tool options 66

Creating curves with edit points 69

Changing the edit point curve shape 70

Setting EP Curve Tool options 71

Creating curves using a pencil 73

Setting Pencil Curve Tool options 74

Creating a curve-on-surface 75

Creating trim curves 75

4 Editing Curves 79Editing curves in the Attribute Editor 79

Transforming curves in the Attribute Editor 80

Using Maya: Modeling v


Accessing the curve’s history 81

Using the Curve Editing Tool 84

Changing the parameter position 85

Transforming the curve tangents 85

Aligning the tangent horizontally or vertically 87

Adding points to a curve 88

Adjusting CVs 90

Inserting knots and isoparms 93

Setting Insert Knot and Insert Isoparm options 96

Extending curves 100

Setting Extend Curve options 101

Offsetting curves and curves on surface 107

Setting Offset Curve options 112

Setting Offset Curve On Surface options 117

Fitting cubic geometry to linear geometry 120

Setting Fit B-Spline options 121

Filleting curves 123

Creating circular curve fillets 123

Creating freeform curve fillets 126

Setting Fillet Curve options 128

Opening and closing curves and surfaces 133

Setting Close Curve options 135

Setting Close Surface options 135

Duplicating curves and isoparms 139

Setting Duplicate Curves options 146

Attaching curves and surfaces 148

Attaching curves and surfaces with history off 148

Setting Attach Curves and Attach Surfaces options 154

Detaching curves and surfaces 156

Setting Detach Curves and Detach Surfaces options 161

Aligning curves and surfaces 165

vi Using Maya: Modeling


Aligning Curves 166

Aligning surfaces 169

Setting Align options 172

Changing the order of the alignment 174

Scaling the tangent and curvature alignment 177

Projecting curve tangents 186

Setting Project Tangent options 188

Adjusting the tangent interactively 191

Reversing the curve or surface direction 195

Setting Reverse Curves options 196

Setting Reverse Surfaces options 197

Rebuilding curves 199

Setting Rebuild Curve options 200

5 Creating and Editing Objects 207Using NURBS primitives 207

Creating objects with NURBS primitives 208

Modifying primitives to build objects 208

Using the Show Manipulator Tool with primitives 211

Setting primitive options 213

Setting Circle options 218

Setting Cylinder options 219

Setting Cone options 221

Setting Cube options 223

Setting Plane options 225

Editing objects in the Attribute Editor 227

Using a construction plane 232

Setting Construction Plane Options 233

Creating and editing text 235

Setting Create Text options 235

Using Maya: Modeling vii


6 Introduction to Surfaces 243What you need to know about surfaces 243

What is world coordinate space? 243

What is an isoparm? 245

What is the U / V surface direction? 246

What are U and V divisions? 246

What is a surface normal? 248

What is construction history? 250

Converting NURBS to polygons 252

Setting NURBS To Polygons options 253

Choosing a tessellation method 254

7 Creating surfaces 259Filleting surfaces 259

Creating circular surface fillets 259

Setting Circular Fillet options 260

Creating free-form surface fillets 266

Setting Freeform Fillet options 269

Blending surfaces 271

Setting Fillet Blend Tool options 274

Revolving surfaces 279

Using the revolve manipulator 280

Editing the input profile curve 282

Setting Revolve options 285

Lofting curves and surfaces 293

Setting Loft options 296

Beveling surfaces 303

Changing the bevel’s dimensions interactively 304

Setting Bevel options 308

viii Using Maya: Modeling


Extruding surfaces 316

Setting Extrude options 317

Preparing to stitch surfaces 328

Creating stitched surfaces 328

Setting Stitch Tool options 332

Stitching surface points 339

Setting Stitch Surface Points options 340

Creating boundary surfaces 346

Creating a four-sided boundary surface 346

Creating a three-sided (triangular) boundary surface 347

Setting Boundary options 349

Creating birail surfaces 356

Using the Birail 1 Tool 357

Setting Birail 1 Tool options 358

Using the Birail 2 Tool 364

Setting Birail 2 Tool options 365

Using the Birail 3+ Tool 368

Setting Birail 3+Tool options 369

8 Editing Surfaces 373Trimming surfaces 373

Setting Trim Tool options 375

Untrimming a trimmed surface 378

Setting Untrim options 378

Planar trimming 380

Setting Planar Trim Surface options 381

Intersecting surfaces 385

Setting Intersect options 387

Projecting curves 390

Setting Project Curve options 391

Using Maya: Modeling ix


Rebuilding surfaces 397

Setting Rebuild Surfaces options 399

x Using Maya: Modeling


Using Maya: Modeling 1

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1 NURBS Modeling

This chapter contains short general descriptions of the Maya tools andactions you use to create and edit NURBS curves and surfaces. It alsocontains information about manipulators, the Attribute Editor and ChannelBox, creating locators, and the Measure tools. A compilation of NURBSmodeling tips and tricks are included at the end of the chapter.

This chapter includes:

• “Modeling basics” on page 1• “Using curves to build surfaces” on page 4• “Creating objects using NURBS primitives” on page 5• “Creating surfaces” on page 5• “Editing curves and surfaces” on page 7• “Creating locators and measuring distances” on page 10• “Using the Show Manipulator Tool” on page 11• “Using the Attribute Editor” on page 22• “Using axes and pivot points” on page 26• “Creating locators” on page 31• “Using Measure tools” on page 33• “NURBS modeling tips and tricks” on page 45

See also Chapter 2, “Introduction to Curves” for information on curve basics,Chapter 6, “Introduction to Surfaces,” for information on surface basics, andfor information on primitives and text curves, see Chapter 5, “Creating andEditing Objects”

Modeling basicsModeling in 3D is different from the conventional 2D drawing process.Imagine working with wire. You first place wires that determine the basicshape of the object, and then cover the wires with a surface that can bepositioned to create motion for an animation. Cover the surface with a skinof almost any material you can think of, set up lights, and take a picture.This is essentially how Maya works.

2 Using Maya: Modeling

NURBS ModelingModeling basics

The surface can be shaped and refined in real time using four views. You canbuild 3D surfaces in many ways. For example, you can start by extruding a2D curve, revolve it or draw boundaries that define it, and then cut areas outof the constructed surfaces by trimming them.

When you are satisfied with the model, you can turn the surface into aphoto-realistic image by adding textures, colors, highlights, andbackgrounds using the rendering functions and options provided. Useraytracing to add highly accurate reflections, refractions, and shadows forsurfaces such as glass and water. And to complete the image, you can addnatural phenomena like fog, sky, and sunsets.

Non-Uniform Rational B-Splines (NURBS) are a special type of spline you useto create smooth curves and surfaces. The curves and surfaces are defined bya set of control points, which influence the object or shape in their vicinity.The overall object shape is determined by the way the control points aredistributed in space. As you move the control points, the curve or surfacechanges shape and follows the control points in an intuitive way that is easyto work with.

Using construction historyMost surface and curve creation tools produce objects with constructionhistory. This means that the original curves or surfaces are still there after asurface is constructed or a curve is modified. By default, a surface withconstruction history is displayed in dark pink.

In the following example, a revolved surface is created from a curve. Thecurve is selected and then extended using Curves → Extend Curve, thuschanging the revolve surface result.

construction curveextended curve



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If you want to turn off construction history before you create a surface, clickthe Construction History On/Off icon from the Status Line.

Now when you create the revolved surface and select the construction curve,you can modify or delete it without changing or deleting the surface.

To delete construction history after a surface is created, selectEdit → Delete by Type → History or Delete All by Type → History. Thesurface reverts to the default inactive color when you select the constructioncurve.

Attaching curves and surfaces with history off

The Attach Curves options window (for both curves and surfaces) contain atoggle that lets you keep the original curves or surfaces after the attach isperformed. Keep Original is toggled on by default. Try not to toggle thisoption off if history is set to on (the Construction History icon in the StatusLine). Odd behavior may occur if the attached curve or surface is latermodified.

Construction Constructionhistory on history off



Animating CVs and construction history

If you animate CVs on an object that was created with history, do not deletethe object’s history. The CV animation will not be correct and unexpectedresults will occur.

Using curves to build surfacesMaya provides three curve creation tools. Surfaces can be built from one ormore curves using one of these methods:

CV Curve Tool

A CV (control vertex) is a point that controls the shape of a curve or surface.The CV Curve Tool is used to create free-form curves. CVs are placed one ata time, and the curve is created when there are sufficient CVs to define atleast one span. For a degree 3 curve, at least 4 CVs are needed to create asingle span. The CVs can be manipulated using transformation tools to givelocalized, predictable modifications to the curves and surfaces. See “Creatingcurves with CVs” on page 61 for details.

EP Curve Tool

An edit point is a point that lies on the curve or surface. Use the EP CurveTool to place points one at a time. The curve is created to interpolate themwith one span between each edit point. See “Creating curves with editpoints” on page 69 for details.

Pencil Curve Tool

The Pencil Curve Tool method is useful for sketching a curve, rather thancreating it by placing CVs or edit points. The Pencil method lets you create acurve as easily as drawing a line on a piece of paper. See “Creating curvesusing a pencil” on page 73 for details.



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Creating objects using NURBS primitivesSeveral simple NURBS objects, such as spheres, cubes, cylinders, cones, andplanes, are called primitives. You can create primitives in a single operationby selecting an item from the Primitives → NURBS menu.

You can create complex objects by combining, transforming, trimming andcutting, or using surface functions, such as filleting, on these simple shapes.Throughout this book, NURBS primitives are used in various surfaceconstruction situations.

You can also create text (Primitives → Create Text) using a variety of fonts.You can specify whether the text curves are NURBS, trim curves, orpolygons.

Creating surfacesThis section includes a brief description of the tools and actions you use toconstruct surfaces using various methods and how to tailor your creations.

Filleting and blending surfaces

Filleting is a fast and easy way to create either a smooth rounded curvebetween two existing curves or a rounded edge between two surfaces. UseSurface fillets (Surfaces → Circular Fillet and Freeform Fillet) to create anobject with rounded edges, or to blend two surfaces together.

For example, you can protrude a NURBS cylinder primitive through a flatsurface and create a smooth rounded edge where the two intersect. Or youcould use the Surfaces → Fillet Blend Tool to join two sphere primitivesusing a free-form surface fillet and transform the top and bottom toconstruct a bottle. Surface filleting functions are also used to create thecurves-on-surface you need to trim a surface.

Revolving curves

Creating a surface of revolution is like using a lathe. First you create asilhouette, or profile, then revolve it.Unlike the lathe, when you useSurfaces → Revolve you can choose whether or not the object completes therevolution. Instead of being limited by a closed 360 degree revolution, youcan specify the number of degrees. For instance, if you want the object to beflat on one side, revolve it by 180 degrees. If it needs to fit in a corner,revolve it by 90 degrees.



Lofting curves and surfaces

Lofting is like building a boat. You construct a skeleton of ribs then apply ahull of skin, planks, or metal sheets to the ribs. In other words, you create aseries of splines that define the shape of the object, then you loft thesesplines together. You can use Surfaces → Loft to create an airplane fuselageor wings, or to create intermediate areas between any two surfaces createdwith boundary curves.

Beveling curves and isoparms

Use Surfaces → Bevel to create an extruded surface with a beveled edgefrom any curve. This lets you create a ledge on a building, for example, orthe piping on an upholstered chair.

Extruding surfaces

An extrusion is defined by two splines—one spline for the outline of theshape, and the other for the path that the outline follows. Extrusions are liketubing that comes out of a machine. They have an outline that remainsconsistent throughout their length. To define the path that the extrusionfollows, use Surfaces → Extrude.

Stitching surfaces

Use Prepare to Stitch to set up your surfaces before a stitching operation isperformed.

Use the Edit Surfaces → Stitch Tool to stitch, or align, two NURBS surfaces.

Use Edit Surfaces → Stitch Surface Points to stitch NURBS surfacestogether by selecting points on the surface.

Creating boundary and birail surfaces

Use Surfaces → Boundary to create three-sided or four-sided surfaces fromthree or four curves. A boundary surface has four edges and can havealmost any three-dimensional shape. Boundary curves (or profile curves) giveyou control over the shape when creating smoothly curved, non-planar 3Dsurfaces. You provide the splines for all the sides, or boundaries, of thesurface to be created. The boundary curves define the surface’s profile, andthe rail curves define the cross-section, which determines how the splinesconnect. Boundary curves are useful when creating complex surfaces thatare not constant in any of three dimensions, but change across the wholesurface.



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You can also use Surfaces → Birail 1 Tool, Birail 2 Tool, and Birail 3+Toolto create surfaces by combining three or four free-form curves that intersect.

Editing curves and surfacesAfter creating curves and building surfaces, you may want to modify themusing specific functions instead of moving points.

Adding points to a curve

After a curve is constructed, you may sometimes find that additional pointsare necessary if you want to move points on a curve. Use Curves → AddPoints Tool to add additional CVs or edit points to a curve or curve-on-surface.

Adjusting CVs

Use Curves → CV Hardness to adjust CVs to build smoother curves.

Inserting knots and isoparms

You may need extra spans on curves or on isoparms on surfaces to provideenough freedom in the curve or surface to be able to create the desiredshape. Use Curves → Insert Knot to insert knots to add additional editpoints on a curve, or Edit Surfaces → Insert Isoparms to insert isoparms ona surface.

Extending curves

Sometimes after you create a curve, you find that it is not long enough tointersect other curves when using another operation (such as a Birail Tool)or you want to use an extension of a particular curve to change a surface(such as a revolved object). Use Curves → Extend Curve to extend a curveor curve-on-surface using a linear, circular, or extrapolation method.

Offsetting curves

Use Curves → Offset Curve to create a curve parallel to the original at aspecified offset distance. To create a curve-on-surface parallel to the originalcurve-on-surface, use Curves → Offset Curve On Surface.

Fitting cubic geometry

Use Curves → Fit B-Spline to fit a cubic curve to a degree 1 (linear) curve.



Opening and closing curves and surfaces

Use Curves → Open/Close or Edit Surfaces → Open/Close to toggle curvesand surfaces open or closed.

Duplicating curves and isoparms

Use Curves → Duplicate Curves to transform a curve-on-surface, aboundary curve, or an interior isoparm of an existing surface into a 3Dcurve.

Attaching curves and surfaces

Use Curves → Attach Curves to join two curves by attaching their endpointsto create a single curve. You an also join two surfaces by attaching theiredges to create a single surface.

Detaching curves and surfaces

Use Curves → Detach Curves or Edit Surfaces → Detach Surfaces to breaka curve into two curves, open a currently closed curve, or detach a surface.

Projecting curve tangents

Use Curves → Project Tangent to modify a curve’s tangent at an endpointso that it coincides with the tangent of a surface or two other intersectingcurves.

Trimming surfaces

Trimmed surfaces let you cut surfaces in three dimensions. Applying one ormore trimming curves to an existing surface creates a new surface with areastrimmed away. Use Edit Surfaces → Trim Tool to select the regions of thesurface to keep or cut away.

To be able to trim a surface, you must have curves-on-surface. There areseveral ways to create such trim curves:

• Make Live. Draw a curve directly onto a surface by first making the surface“live” (click the Make Live icon on the Status Line), then drawing on thesurface using any of the curve creation tools.

• Project Curve. Project a curve onto a surface using Edit Surfaces → ProjectCurve.



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• Intersect. Intersect two surfaces using Edit Surfaces → Intersect Surfaces, oruse one of the surface filleting functions. You can optionally create trimcurves on the surfaces when using these functions.

Trimming planar curves

Use Surfaces → Planar to quickly covert a planar curve into a surface. Theresulting surfaces look like shapes stamped out of sheet metal.

Intersecting surfaces

Use Edit Surfaces → Intersect Surfaces to intersect one object with another.Intersections can also be used to create the curves-on-surface you need totrim a surface.

Filleting curves

Use Curves → Fillet Curve to create a bridge between two curves.Theresulting curves have the exact amount of roundness required, and thecurves do not necessarily have to intersect. There are two ways to constructcurve fillets—Circular and Freeform. You select the type you want from theoptions window (Curves → Fillet Curve - ❐).

Aligning curves and surfaces

Use Curves → Align Curves to establish continuity between curves orsurfaces. Use manipulators to align the elements interactively.

Reversing the curve or surface direction

Use Curves → Reverse Curves and Edit Surfaces → Reverse Surfaces toreverse the sequence (or direction) of CVs on a curve or surface. You canalso reverse the surface normals for surfaces and trimmed surfaces.

Rebuilding curves and surfaces

Sometimes after a sequence of modeling operations, surfaces grow incomplexity and become cumbersome and slow to work with. Use EditSurfaces → Rebuild Surfaces to change the number of patches or the degreeof a surface. This lets you reduce the number of patches on a complexsurface. Use Curves → Rebuild Curve to recreate a curve or a curve-on-surface to reduce data and construct smoother curves.



Creating locators and measuring distancesYou can replace primitives with locators to control other objects. Forexample, you can create these locators, connect them to expressions, and usethem as control objects instead of primitives. The main advantage to this isthat locators don’t render. This way, you don’t have to remember to turncontrol objects off before rendering. Also, locators don't slow down yourscene. This is another advantage over using spheres or planes as controlobjects.

Creating locators

Use Primitives → Create Locator to create a locator to mark a position inworld space.

Maya also provides measure tools to measure distances and displayparameters on the curves and surfaces you create.

Measuring distances

Use Modify → Measure → Distance Tool to measure and display distancesbetween two specified points.

Displaying parameter values

Use Modify → Measure → Parameter Tool to display parameter values oncurves and surfaces at a specified point.

Measuring arc lengths

Use Modify → Measure → Arc Length Tool to measure and display arclengths on curves and surfaces at a specified point.


NURBS ModelingUsing the Show Manipulator Tool

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Using the Show Manipulator ToolSome functions display special manipulators that let you tailor a surface orcurve after a surface has been created. Use the Show Manipulator Tool toedit the construction history of an operation or sometimes, the attributes ofan object itself. In other words, this tool lets you access the input node of anobject.

To access and display manipulators:

There are several ways to access and display manipulators using the ShowManipulator Tool. Before you start, make sure construction history is on.

1 For a surface constructed with curves (such as an extruded surface), setCurve Range to Partial in the options window.

2 Click the Show Manipulator icon .

3 In the Channel Box, click the heading for the subCurve you want to edit.

Curve Rangeset to Partial



or

For an active object such as a NURBS primitive or a revolved surface, clickthe Show Manipulator icon and click the item’s heading in the Channel Box.

Selecting an item’s history nodeThe Show Manipulator Tool associates a manipulator with the history nodeof the operation, therefore, to access the manipulator the history node has tobe selected.

For example, to edit the parameters of a revolve operation after the revolvehas been performed, select the operation’s history node. If you performseveral other operations and then want to edit the revolved surface, themanipulators are no longer displayed. You have to select them using one ofthe following methods.

To select the history node:

1 Select the revolved surface.

2 On the keyboard, press the letter “a”, and with the left mouse button click-drag to Select All History from the marking menu in any view.



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or

From the History list menu in the Status Line, select Revolve.

or

From the Channel Box, select the history node (revolve1).

In the following example, the history nodes for a revolved surface and thecurve used to construct it are selected. Click revolve1 to select the historynode for the revolved surface.

Tip

Select All History can display manipulators for multiple history nodes. Toedit the node you need, click the headings in the Channel Box to selectwhich one you want to edit, or open the Attribute Editor and select theproperties you want to change.



Click subCurve1 to select the history node for the construction curve.

Once the history nodes and the Show Manipulator Tool have been selected,manipulators are displayed on the surface or the construction curve. Tointeractively edit these nodes, click and drag the manipulators, or change thevalues in the Channel Box or the Attribute Editor.

Changing a curve’s parameter rangeA subCurve is created when you select the Partial option as the CurveRange in some of Maya’s options windows. This option lets you select aminimum and maximum parameter value on the curve, and only the part ofthe curve between those points is used in the creation of the surface. Mostsurfaces that use a curve as input include this option.

A subCurve can also be the construction curve, or input curve, you use tocreate surfaces, such as revolved or extruded surfaces.

Editing a subCurve in the Channel BoxYou can edit a subCurve history node interactively using manipulators, oryou can enter values in the Channel Box and Attribute Editor. In thefollowing example, you create an extruded surface and modify itssubCurves (the input curves, profile, and path, used to create the extrudedsurface).

Tip

Some options windows include a Keep Original toggle. Toggle this on toaccess the manipulators (for example, Curves → Detach Curves).



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To edit a subCurve from the Channel Box:

1 Before you create the extruded surface, set the Curve Range to Partial in theExtrude options window.

2 Create the extruded surface from a curve and a primitive circle.

3 To display the curve range manipulators on one of the partial input curves(in this case, the path curve, which is subCurve2), click subCurve2 in theChannel Box and select the Show Manipulator Tool (if it is not alreadyselected).

4 To change the parameter value, drag a manipulator handle.



You can also enter values in the Channel Box to change the parameter valuewithout using the manipulator.

5 To edit the input profile curve, click subCurve1.

If you want to perform another function on the extruded surface and lateredit the subCurve, you can select the subCurves you need from the ChannelBox.

Tip

You can also type values in the Numerical Input line for the currentmanipulator handle if you do not want to leave the Channel Box open.Add the subCurve to the history menu to select it from there instead. See“Adding a subCurve to the History menu” on page 17 for details.



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Adding a subCurve to the History menuIn order to select a subCurve from the History list menu in the Status Line,you have to add it to the menu first.

To add a subCurve to the History menu:

1 From the bottom of the History list menu, select Complete list.

2 In the History list window, select List from the Filter pop-up menu.

The subCurve is now included in the History list menu.



This means, instead of selecting the subCurve manipulator from the ChannelBox, you can select it from the History list menu on the Status Line. You canalso access an Attribute Editor for the subCurves by clicking the option box(❐) beside the heading. See “Editing subCurves in the Attribute Editor” onpage 19 for details.

Accessing a subCurve from the marking menuOnce you add the subCurve to the History menu, you can also access itthrough the marking menu.

To access a subCurve from the marking menu:

1 Place the pointer over the surface that was created with the subCurve (suchas a revolved surface with a partial curve) while the surface is active.

2 Press the right mouse button and click the triangle beside Inputs to displaythe pop-up menu.

Note

Adding a subCurve to the menu is done on a per-object basis, meaning ifyou create another surface using a partial curve, that subCurve will notappear in the menu.



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Editing subCurves in the Attribute EditorSelect Object → subCurve1 - ❐ to open the Attribute Editor for a subCurve.(Since some operations require that you use more than one subCurve, thenumber after a subCurve heading represents the subCurve you want toedit.)

Once a subCurve has been added to the History list menu, you can also openthe Attribute Editor for the subCurve by clicking the option box (❐) besidethe Sub Curve heading in either the History list menu from the Status Lineor the Inputs pop-up menu from the marking menu.



Setting SubCurve Attributes

Input Curve

The Input Curve text box is read-only. Click the arrow beside the box toaccess the curve you want to edit and to open its Attribute Editor.

Min/Max parameter values

The Min Value and Max Value parameter boxes are the same ones you see inthe Channel Box. You can enter values here and press the Select button orpress Enter to update the subCurve.

Relative

Use the Relative toggle to turn the relative addressing mode on or off.Relative is toggled on by default. If toggled off, the mode is absolute,meaning the actual parameter range of the curve is used. If toggled on, theparameter range of the curve is treated as though it were from 0 to 0.



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Editing parameters with manipulatorsTo display manipulators for the NURBS sphere, NURBS cylinder, andNURBS cone primitives, select the Show Manipulator Tool while theprimitive is active. Then click the object’s heading in the Channel Box, selectit from the History list menu in the Status Line, or from the marking menuInputs pop-up menu. Click-drag the manipulator handles to edit the object.

For example, to display the manipulators for a NURBS cone primitive fromthe Channel Box, first select the Show Manipulator icon, then click the cone’sheading (makeNurbCone1):

To display manipulators from the History list menu, drag to the Make NurbCone heading and release the mouse button.

To display manipulators from the marking menu, place the pointer over theactive NURBS cone, press the right mouse button and drag to select theMake Nurb Cone heading from the Inputs pop-up menu, and release themouse button.


NURBS ModelingUsing the Attribute Editor

Editing attributes with manipulatorsIn some cases, a manipulator is associated with the parameters of an objectitself. Examples include texture projection nodes, cameras, polygons, joints,and all light types. To display the manipulators, select the ShowManipulator Tool on one of these active items (or select it before you createthe item). See the Animation and Rendering books and the “PolygonalModeling” section of this book (Chapter 1, “Polygonal Modeling”) to find outmore about these manipulators.

Using the Attribute EditorThe Attribute Editor is used as an editor for all nodes. This means thatsurfaces, curves, and any selectable item can be displayed in this onewindow. You can use the Attribute Editor in addition to the Channel Box toedit various nodes and operations for a specific operation.

Accessing the Attribute EditorBesides selecting Window → Attribute Editor for an active item, there areseveral ways to access the information you need to edit. The followingexample shows how to set the options in the Attribute Editor for a filletedcurve.



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To access the Attribute Editor:

Select the fillet curve to make it active. Click on the curve, or select itsheading from the Channel Box.

• In the Channel Box, select Object → filletCurve1 - ❐.

• From the History list menu in the Status Line, select Fillet Curve - ❐.

• From the marking menu, press and hold the right mouse button while thepointer is over the active curve. Drag to the Inputs pop-up menu, selectFillet Curve - ❐ and release the mouse button.

Click to select the... or select the node in thefillet curve in the view...Channel Box.

From the Channel Box From theHistory list menu



A node’s history section of the editor (in this case, the Curve Fillet Historysection) includes all the information related to the creation of an item.

Drag to here and release themouse button to open theAttribute Editor.



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In this example, the editor contains the nodes for the input curves and thevarious options that were set in the options window for a curve fillet,including:

Curve Parameter values

These values correspond to the fillet’s param manipulators you see when theShow Manipulator Tool is selected. These parameter values define the regionbetween the two original curves where the fillet curve is created.

Input Curve

This read-only information gives you access to the history of the curves youused to create the fillet. Click the arrow buttons to select an input curve andopen its section of the editor.

Other attributes

Other curve fillet-related options which are also included in the Fillet Curveoptions window.

Temporarily blocking (or hiding) a nodeThe Attribute Editor also includes generic information for all nodes. Thefollowing describes the Node Behavior section.

If you select Blocking from the Node State pop-up menu, your surfacetemporarily becomes invisible. This can be very useful when you havecomplex scenes and want to edit only one facet of a surface.

For example, let’s say you have a complex revolved surface and want to editthe curve, but you don’t want to wait while the revolve re-draws. You canselect Blocking and edit the curve.

To see the results, select the revolve surface’s node (either from the ChannelBox or the History list menu), and then select Normal from the Node Statepop-up menu in the Attribute Editor.


NURBS ModelingUsing axes and pivot points

Using axes and pivot pointsThere are various ways you can define where your objects are transformedfrom. You use the location of the pivot point or axes to transform in aspecific direction from a specific point in local or world space.

What are pivot points?Objects are transformed based on a specific point in 3D space known as apivot. When you rotate a primitive, for example, the pivot point representsthe center of the rotation axis; when you scale, the pivot point represents thefixed point around which scaling occurs.

By default, the pivot point is set so that the rotational and scale pivots arelocated at the point of origin for an object (0, 0, 0). The point of origin is thecenter of the object. A quick way to change an object's pivot when in atransformation tool is to use the Insert key on the keyboard to toggle to andfrom an edit mode. Edit mode displays a manipulator for moving the pivot.For more details, see the section describing the transformation tools in theBasics book.

To quickly display and reposition pivot points:

You can move the pivot point to determine at which point you want tomove, scale, or rotate the object from. Use the Insert key on the keyboard todisplay the pivot point, then use any of the transformation tools. In thefollowing example the Rotate transformation tool is selected.

1 While an object is active, select a transformation tool, then press the Insertkey. The manipulator appears; use it to move the pivot point.



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2 Drag the manipulator to move the pivot point.

3 Press the Insert key again to display the rotate manipulator, drag to rotatethe object.

To display the pivot point from the Attribute Editor:

1 Open the Attribute Editor (Window → Attribute Editor).

2 To display the pivot points for models, toggle Display Rotate Pivot orDisplay Scale Pivot on in the Pivots section under the object’s transform tab.



To reposition the pivot point using the Attribute Editor:

1 While the object is active, open the Attribute Editor and toggle DisplayRotate Pivot on.

2 In the Local or World Space sections, enter a value for Rotate Pivot andpress Enter. In the following example, the pivot is moved 5.0 units in the Zdirection in absolute local space. You can now rotate the object from thatpivot point location.

Rotate pivot pointmoved 5.0 in Z



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What is an axis?An axis is a straight line that indicates the origin and direction. For example,by using two axes, a plane is determined: the XY plane is defined by placingX and Y axes so they intersect at the origin. Three dimensions aredetermined by using three axes: X, Y, and Z.

Displaying the axis indicatorsTo display the global axes at the origin in the perspective view, selectDisplay → Axes → Origin from the menu bar.

To display the local axis in all views for an active object, open the AttributeEditor. In the Display section under the objects’s transform section of theeditor, toggle Display Local Axis on.



Changing the origin and direction of the axesIn the Transform Attributes section of the Attribute Editor, you can changethe rotation order of the axes for an object by selecting Rotate Order fromthe pop-up menu. You can also enter values in the Rotate Axis X, Y, or Zboxes to rotate the axes in a specific direction, and to rotate the object arounda different axis.

Toggling the axes origin from the Command LineYou can also type the following commands in the Command Line to togglethe global axis display on and off in the 3D views.

Command Action

toggleAxis -o true; displays the axis at the origin

toggleAxis -o false; hides the axis at the origin

toggleAxis -v true; displays the axis at the bottom left of each view

toggleAxis -v false; hides the axis at the bottom left of each view


NURBS ModelingCreating locators

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Creating locatorsUse Primitives → Create Locator to create a space or curve locator.

A locator marks a position in world space. A locator is displayed as a smallgnomon; its lines extend in each direction along the X, Y and Z axes (like thedirectional rods of a sundial). You can use point snapping to snap to alocator position.

To create and move a locator:

1 Select Primitives → Create Locator. A locator is created at the origin.

2 Use the Move Tool to position the locator.

Repositioning the locator in the Attribute EditorYou can reposition the locator in local space from the Attribute Editor. Toopen the Attribute Editor, either:

• Click the option box (❐) in the Object pop-up menu in the Channel Box.

• Click the option box (❐) in the History list menu on the Status Line.

• Click the option box (❐) in the Inputs pop-up menu in the marking menu.

• Select Window → Attribute Editor.


NURBS ModelingCreating locators

Click the locatorShape# tab to open that section of the editor. Enter X, Y, or Zvalues in the Local Position boxes.

You can transform the locator three ways:

• Use the transformation tools.

• Change the transformation values in the Channel Box.

• Click the locator# tab in the Attribute Editor and change the Transformationvalues in that section of the editor.


NURBS ModelingUsing Measure tools

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Using Measure toolsThe Measure menu includes the Distance Tool, Parameter Tool, and ArcLength Tool. Click the triangle beside Measure in the Modify menu todisplay the cascading menu.

Using distance measuresUse the Measure → Distance Tool to measure and display distancesbetween two specified points.

To display a distance measure:

1 Select Modify → Measure → Distance Tool.

2 Click to select two points in space, or click on a curve or surface to displaythe distance measure locator.


NURBS ModelingUsing distance measures

The following example shows the distance locator when two points areplaced on a surface.

This shows the distance locator when one point is placed in world space andthe other is placed on the surface.

The following shows the distance locator when two points are placed on acurve.

To snap a distance measure point:

If you want to snap a locator to a curve or surface, use the Snap to curvesicon and click on the curve or surface. When you move the item, the distancemeasure updates. This can be especially helpful if you want to measure thedistance between two curves.

1 Click the Snap to curves icon from the Status Line.

2 Place a point on one curve and another point on the other curve.



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3 Move one of the curves and the distance measure updates.

To move the distance locator:

Select the Move Tool, then click to select a locator and drag to where youwant to measure the distance between. The distance measure updatesinteractively.



Editing the distance locators in the Attribute EditorIf you want, you can specify the start and points of the distance measure inX, Y and Z from the Attribute Editor. To open the Attribute Editor, either:





To specify the start and end points of the distance measure:

Click the distanceDimensionShape# tab to open that section of the editor.Enter values in the Start Point and End Point boxes to specify the start andend points of the distance measure in X, Y, and Z.

To reposition the distance locator in local space:

Click the locatorShape# tab to open that section of the editor. Enter values inthe Local Position boxes to reposition the distance measure in X, Y, or Z.



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NURBS ModelingDisplaying parameter values

Displaying parameter valuesUse the Measure → Parameter Tool to display parameter values on curvesand surfaces at a specified point. This locator also displays the direction ofthe curve or surface and the normal to the curve or surface at a specifiedpoint.

To display parameter values on a surface or curve:

1 Select Modify → Measure → Parameter Tool.

2 Click-drag on a curve or surface to display the parameter values at aspecified point.

For curves, the parameter value in U at the specified point on the curve isdisplayed.

Normal

Surface direction

Normal

Curve direction



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For surfaces, the parameter value in U and V at the specified point isdisplayed.

To move the parameter locator:

Select the Move Tool, then click-drag a locator over the curve or surface. Theparameter values update as you drag.

If you create another locator, the previous locator is dimmed. This meansthat you can move it later if you need to.



Editing the parameter locators in the Attribute EditorIf you want, you can specify the U and V parameters values from theAttribute Editor. To open the Attribute Editor, either:





Click the arrow beside the Nurbs Geometry box to access the curve orsurface whose locator you want to edit.

To specify the U and V parameter values:

Click the paramDimensionShape# tab to open that section of the editor.Enter new U and V Param values.


NURBS ModelingMeasuring arc lengths

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In the following example, the first figure shows the parameter locator on asurface at the position where it was created. The second figure shows howthe locator is modified when you change the U and V Param values.

Measuring arc lengthsUse the Measure → Arc Length Tool to measure and display arc lengths oncurves and surfaces at a specified point. It also displays the direction of thecurve or surface and the normal to the curve or surface at a specified point.

To display arc length values on a surface or curve:

1 Select Modify → Measure → Arc Length Tool.

2 Click-drag over a curve or surface to display the parameter values at aspecified point.

Normal Normal

Surface direction Curve direction



For curves, the distance of the specified point from the start point of thecurve is measured.

For surfaces, the specified point from the start point in both the U and Vdirection is measured.

To move the arc length locator:

Select the Move Tool, then click- drag over the curve or surface. Theparameter values update as you drag.

If you create another locator, the previous locator is dimmed, meaning youcan select to move it later if you wish.



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Editing the arc length locators in the Attribute EditorIf you want, you can specify the U and V parameters values from theAttribute Editor. To open the Attribute Editor, either:





Click the arrow beside the Nurbs Geometry box to access the curve orsurface for which you want to edit the locator.

To specify the U and V parameter values:

Click the arcLengthDimensionShape# tab to open that section of the editorand enter new U and V Param values.



In the following example, the first figure shows the arc length locator on asurface at the position where it was created. The second figure shows howthe locator is modified when the U and V Param values are changed.


NURBS ModelingNURBS modeling tips and tricks

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NURBS modeling tips and tricksThe following information can be useful to get you started or if you run intoproblems. A few special tricks are also included.

Tools and actionsBecause Maya works on a selection-based mode, picking items is critical tomodeling. If you forget what needs to be picked for a tool or an action, holdand drag the mouse button over the menu item. The Help Line displays thetype of selection required for the current item.

What is a tool?If something is a tool, it contains the word Tool after its name (for example,Curves → CV Curve Tool). When using a tool, first set the options in theoptions window, select the tool, and then select the item. After the operationis complete, you can change the object’s attributes in the Channel Box orAttribute Editor if necessary.

What is an action?If something is an action, you have to select the item first and then theaction. For example, if you want to create a revolved surface, first select theprofile curve you want to use, then select Revolve from the Surfaces menu.

Workflow tipsThe following are some handy tips and tricks that can help to get youstarted.

Using marking menus when modeling

Select Options → Customize UI → Marking Menus. In the Marking Menuseditor, do the following:

1 With the left mouse button, click to select a mouse button style (for example,PA_Style_LMB).

2 Select the Hotbox option from the Use Marking Menu in pop-up menu.



3 Select the Center option in the Hotbox Region section, and click to turn theLeft toggle on in the Mouse Button(s) section.



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4 Click Apply Settings to assign a specific series of actions to the left mousebutton.

5 Repeat this for the middle and right mouse buttons. Once completed, clickClose.

Hiding the HotboxA Hotbox is available for each of the four menu sets: Animation, Modeling,Dynamics, and Rendering. Marking menus are activated by pressing thespace bar and pressing the left, middle, or right mouse buttons. When youpress and hold the space bar, the Hotbox is displayed. Now if you press theleft mouse button, a set of marking menus is displayed on top of the hotbox.

The hotbox can be distracting when it is under the marking menus, so youcan disable it if you want to.

To hide the Hotbox:

1 While holding down the space bar, press a mouse button over the HotboxControls menu.

2 From the Hotbox Style menu, select Center Zone Only.

Selecting this option hides the Hotbox and when you press the space bar anda mouse button, only the marking menus are displayed.

3 To reopen the hotbox, press the space bar and use the left mouse button toselect Zones and Menu Rows from the Hotbox Style menu.

Modeling tipsBecause many of the modeling functions in Maya are command based, theselection order is critical. There are times when you have to select differenttypes of entities, such as isoparms (surface curves) or points on a surface.

Picking mode tipsFor example, when lofting between a curve and the edge of a plane, youhave to select the curve first in object selection mode, and then the plane’sisoparm edge in component selection mode.



To reduce the number of picking steps:

1 Click the Select by hierarchy and combinations icon, the first mini icon inthe row of the Status Bar. To the left of this button, the word Hierarchy isdisplayed in a box.

2 Click the arrow to the left of this box to display a pull-down menu.

3 Select NURBS to change the selection mode so that you don’t have to knowif an isoparm, a curve, or a curve point has to be active to select something.

This mode places an override on the selection mode and lets you pick whatyou want without worrying which mode you are working in.

This works well for modeling, but it can be cumbersome to continuouslyselect this option. For this reason, the right mouse marking menu lets youselect the kind of component you need when over an active object. You’llnotice throughout this book that various modes of selection are used to letyou choose to adopt a method that you’re comfortable with.

Picking and displaying historyA quick way to pick and display history, such as a subCurve history node, isto press the “a” key and use the left mouse button to select Select AllHistory from the marking menu in any view.



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In some cases, there may be multiple history nodes. To edit the node youneed, simply click the headings in the Channel Box to select which node youwant to edit, or open the Attribute Editor and select the attributes you wantto change.

Stepping backwards in construction historySome operations, such as Stitch, Align (with join turned off), and CurveFillet, produce an intermediate object. This is an invisible copy of theoriginal. To see and select this object, first select the visible result, then pressCtrl i to select the original surface.

If you are animating the CVs of an object that has an intermediate object,animate the CVs of the intermediate object for better results.

Deleting CVs on a surfaceTo delete a row of CVs on a surface, select more than one CV in that row,select the hull that corresponds to that row of CVs, then press the Backspacekey. Do the same thing if you want to delete a column of CVs on a surface. Ifyou select only a single CV, both the row and the column are deleted.

Using commandsThe following commands can save you time when using any Maya tool oraction.

Assign commands to an aliasUse the ‘alias’ MEL command in your favorite shell. It saves lots of typing,especially if you frequently use commands with the same sets of non-defaultparameters.

Display attribute dependenciesUse affectedNet command to set up a dependency graph consisting ofnodes that represent the attributes of a specific node (or type of node).Connections represent how the source attribute affects the destinationattribute.



Prevent offset of CVs on NURBS with clustersIf you create a cluster with NURBS CVs in it, and then try to drive other CVson the same NURBS object using the connectAttr command, the other CVsare offset. To prevent this offset, change this attribute before you make theattribute connection:

setAttr .relativeTweak false;

Organizational tipsThe following tips can help when you use the Outliner or Hypergraphwindows.

Open the full hierarchy with one clickIn the Outliner, if you Shift-click the expand/contract triangle, you can openor close the whole hierarchy for the object at one time.

Reorder and reparent in the OutlinerWith the middle mouse button, drag and drop selected objects onto a groupnode to reparent it. Drag and drop selected objects at the bottom of theOutliner to reparent it directly under the world.

Reorder and reparent in the HypergraphDrag and drop one node onto a sibling node in the hypergraph whilepressing the Ctrl key to reorder the nodes.

Warning!

Do not toggle this attribute on and off at whim as it may produceunwanted results.



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Special scriptsThese special scripts provide you with a fast and easy way to performoperations similar to the Power Animator functionality.

To use Power Animator’s Attach or Blend functionality:

Select a NURBS surface isoparm and enter the following in the CommandLine:

attachBlendCurve

or

Select a NURBS surface isoparm (to define the attach direction) and enter:

attachBlendSurface

To create a Power Animator Round surface:

1 In a curve tool’s options window, set the Curve Degree to Linear.

2 Turn Snap to grids on in the Status Line and create a linear square curve.

3 Close the curve using Curves → Open/Close Curves.

4 In the Bevel options window (Surfaces → Bevel - ❐), set the followingoptions:

Bevel Cap Edge to Convex

Bevel Corners to Circular Arcs

5 Click the Bevel button in the options window.



6 To put a lid on the surface, select the end (square) isoparm of the bevelsurface and select Surfaces → Planar.


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2 Introduction to Curves

To build a model, you usually start by building curves that are combined tocreate surfaces. You can create curves with CVs and Edit Points, or drawfree-form curves using the Pencil method. See Chapter 3, “Creating curves,”for details about these curve creation methods.

The following topics are discussed in this chapter:

• “Curve basics” on page 53

• “Creating the perfect curve” on page 54

• “What is the curve degree?” on page 55

• “What is parameterization?” on page 56

• “Which curve creation method should you use?” on page 54

• “What are CV curves?” on page 57

• “What are edit point curves?” on page 58

• “Deleting curve segments” on page 58

• “Deleting CVs on a surface” on page 59

Curve basicsOnce you create a curve, or a spline, you can build a surface from it.

B-splines are a series of polynomial curve segments that join to form onecontinuous curve. The degree of the polynomials is from 1 to 7. In Maya, youcan draw splines to create complex shapes using a variety of editing tools.

The following shows the basic elements of a curve.


Introduction to CurvesCreating the perfect curve

• The start of the curve is indicated by a small hollow box at the first CV.

• The curve direction is displayed as a small letter u.

• A hull is the visual line that connects the CVs.

• The curve between two edit points is called a span. By modifying one ormore spans, you change the shape of the curve.

Creating the perfect curveThere are various methods you can use to create your curves. When youcreate curves, there are certain factors to keep in mind, such as the curvedegree, or how many spans you need. The following should help whentrying to decide what type of curve you need for a particular project.

Which curve creation method should you use?

Try to create simple curves because they are easier to control. Curves withless CVs are simpler and easier to manipulate.

CV

Start of curve

Curve direction

Span

Hull

Edit point

Edit point curveCV curve



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The main advantage of using an edit point curve is that it interpolates thepoints you place. In other words, build a curve with edit points if you needit to pass through certain points. When you place CVs, the curve only passesthrough the end points.

What is the curve degree?The higher the curve degree, the smoother the curve, and the greater thenumber of points needed to define a single curve span. Two points define alinear curve span, three are needed for quadratic curves, and four arerequired for a cubic curve (the CV Curve Tool default).

The following shows a curve constructed with nine points using differentcurve degrees. The first curve (the default) is used as a guide to show thedifference between curve degrees. All the other curves are drawn on top of itfor illustrative purposes.

Tips

Before you place the points to construct a curve, open the options windowfor the curve tool you want to use. You can set specific options such as thecurve degree or whether you want to use uniform or chord knot spacing.

If you need more localized control, you can insert knots to add points. See“Inserting knots and isoparms” on page 93 for more information.

Degree 1 (Linear) Degree 2 (Quadratic)Default degree 3 (Cubic)

Degree 5 (Quintic) Degree 7 (Heptic)



Degree 1 curves have sharp corners at the edit points; degree 2 curves aretangent continuous at edit points, but not as smooth. Degree 3 curves areused more often since they work best with most modeling operations andthe result is a smooth curve with not too many points.

What is parameterization?Parameterization specifies how knot spacing relates to the U parametervalues assigned to edit points.

Chord length If the curve is created with Chord length knot spacing, the parameter valueis determined by the position of the point along the length of the curve. Aninitial parameter value of 0 is assigned to the start of the curve; the value isincreased proportionally to the chord length between edit points.

Uniform If the curve is created with Uniform knot spacing, the parameters haveequally spaced values (0, 1, 2, and so on) at edit points. The parametervalues of a uniform curve always range from 0 to the total number of spanson the curve. A parameter value of 0 is assigned to the start of the curve; thisvalue is incremented by 1 for each edit point along the curve.

Tips

You need degree 3 or higher to achieve C(2) or G(2) continuity betweencurves.

You cannot change the curve degree from the Attribute Editor. Use theoptions window.

Tip

Uniform knot spacing produces a curve with a more predictableparameterization. Chord knot spacing produces a better curvaturedistribution, and, when used to build surfaces, better texture mapping.

Uniform curves have more straightforward parameterization and are usedmore often than chord length curves. Uniform parameters can be easilysubdivided based on edit points; this makes it easier to use Insert Knot ifyou need to add spans later.



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What are CV curves?A CV is a point that controls the shape of a curve or surface. It is displayedas a small filled box. Use the CV Curve Tool to create these kinds of curves.

How to select CVsThere are two selection modes you can use to select CVs: from the StatusLine and from the marking menu.

Selecting CVs from the Status Line

While the curve is active, click the Select by component icon on the StatusLine, click the Points icon, and select CVs from the pop-up menu.

Selecting CVs from the marking menu

Place the pointer over an active curve and press the right mouse button todisplay the marking menu. Drag to Control Vertex, then click to select theCV or CVs you want to edit.



What are edit point curves?An edit point is displayed as a small letter x. The areas where polynomialsare joined are called edit points (sometimes known as knots). Edit points liedirectly on the spline. You can add edit points to an existing curve withoutaffecting its shape. When you add edit points to a curve, you create morespans on the curve. As the number of spans increases, you have morelocalized control over the curve. Use the EP Curve Tool to create this kind ofcurve.

How to select edit pointsLike CVs, edit points can be selected using the Status Line icons or themarking menu.

Selecting edit points from the Status Line

While the curve is active, click the Select by component icon on the StatusLine, click the Parm Points icon, and select Edit Points from the pop-upmenu.

Selecting edit points from the marking menu

Place the pointer over an active curve and press the right mouse button todisplay the marking menu. Drag to Edit Point, then click to select the editpoint or edit points you want to edit.

Deleting curve segmentsTo delete curve segments while you are creating a curve, press theBackspace key on the keyboard.

To delete curve segments after the curve is created, select the CVs or editpoints and then press the Backspace key.



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Deleting CVs on a surfaceTo delete a row of CVs on a surface, select more than one CV in that row orselect the hull that corresponds to that row of CVs. Do the same thing if youwant to delete a column of CVs on a surface. If you select only a single CV,both the row and the column are deleted.

Note

When you create a curve using the Pencil Curve Tool, you cannot deletecurve segments by pressing the Backspace key. Instead, once the curve iscreated, select CVs or edit points (in component selection mode) and thenpress the Backspace key.

Single CV

Three CVsin the samerow.


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3 Creating curves

Since curve creation methods are tools, first adjust the option settings in theoptions window for the tool before you create the curves. If you create thecurves with the default option settings, you can later edit the completedcurve in the Attribute Editor.

The following topics are described in this chapter:

• “Creating curves with CVs” on page 61

• “Creating curves with edit points” on page 69

• “Creating curves using a pencil” on page 73

• “Creating a curve-on-surface” on page 75

Creating curves with CVsA CV is a point that controls the shape of a curve or surface. Use the CVCurve Tool to create free-form curves. You can manipulate CVs usingtransformation tools to give localized, predictable modifications to yourcurves and surfaces.

Before you begin

When you construct a curve with CVs, you must place several points tocomplete the curve, depending on the curve degree setting in the optionswindow.

The following example uses the default curve degree of Cubic, degree 3.Since you need one point more than the curve degree, you have to place atleast four points to construct the curve. See “About curve degrees” on page67 for more information.

Tip

Remember, more CVs doesn’t necessarily mean easier control. You shouldtry to keep the number of isoparms to a minimum.


Creating curvesCreating curves with CVs

To create a curve with CVs:

1 Select Curves → CV Curve Tool.

2 Position the pointer in any of the views where you want the curve to begin.

3 Click to place the first CV. The first CV is displayed as a small hollow boxthat indicates the start point of the curve.

4 Click where you want to place the second CV. This CV is displayed as asmall letter u.

Once you place the CV, a line joins the two CVs. This is the hull line. Thehull line is part of the control polygon and does not represent a curve orcurve segment.

5 Click to place a third CV. Another hull line is created to connect the secondand third CVs. The curve is not built yet since this is a degree 3 curve (Cubicby default) and you have to place at least four points.

6 Click to place the last and fourth CV. When you place the fourth CV, a curvesegment is created that interpolates the first and last CVs.

As you continue to place CVs, new curve segments are created and the curvecontinually updates to interpolate the last CV placed.

Tip

If you hold the mouse button while you click, the CV can be dragged toany location in the view. Release the mouse button to place the CV.

2

34

1



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1 Select the NURBS surface.

2 Click the Make Live icon on the Status Line (or select Modify → Make Live)to make the surface live.

3 Select Curves → CV Curve Tool and place the curve-on-surface CVs directlyon the live surface.

Changing the CV curve shapeOnce a CV curve is drawn, or while you are drawing it, you may want tomodify its shape. You can use the transformation tools to move, rotate, orscale CVs to change the shape of your curves.

To change the shape of the curve as you create it:

1 Before you press Enter to complete the CV curve, press the Insert key on thekeyboard. This displays a move manipulator, which appears on the CV atthe end of the curve by default.

Tip

To complete the curve so you can start to place new curve points, pressEnter.



2 Drag the manipulator to move the CV and to change the curve’s shape.

3 To continue to change the curve’s shape, click with the left mouse button toselect another CV and drag the manipulator.

To change the shape of the curve after it is constructed:

1 Click the Select by component type icon from the Status Line.

2 Click the Points icon, press the right mouse button to display the pop-upmenu, then toggle CVs on.

Tip

You can marquee-select more than one CV at a time.

Remember to press the Insert key to continue placing CVs.



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or

While the pointer is over an active CV curve, use the right mouse button anddrag to select Control Vertex from the marking menu.

3 Click to select the CV (or CVs) you want to move.

4 Select a transformation tool, (in this example, the Move Tool), and drag themanipulator to move the CV.



Setting CV Curve Tool optionsSet the tool options before you create the curve. To open the optionswindow, select Curves → CV Curve Tool - ❐.

To change the options after the curve is created, use the Channel Box or theAttribute Editor. See “Editing curves in the Attribute Editor” on page 79 fordetails.

Changing the curve degree

Select a Curve Degree option to specify the curve degree.

1 Linear curves are often referred to as polylines (linear segments), degree 2curves as quadratics, degree 3 Cubic curves as cubics (the default), degree 5as quintic, and degree 7 as heptic. The higher the curve degree, the morepoints you need to define a single curve span. If the number of controlpoints is the same and the curve degree is high, the curve looks as though ithas more tension than if the degree is low.



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About curve degreesEach curve segment is defined and controlled by n+1 CVs, where n is thedegree of the curve.

For example, a curve of degree 5 requires 6 CVs to form a curve segment.

A curve of degree 7 requires 8 CVs.

Changing the knot spacing

The type of knot spacing relates to the U parameter values assigned to CVs(also referred to as parameterization). Select an option for Knot Spacing.

Chord length If you create a curve with Chord length knot spacing, the parameter valuedepends on the distance along the length of the curve. An initial parametervalue of 0 is assigned to the start of the curve, then the value is increasedproportionally to the chord length between edit points.

Uniform If you create a curve with Uniform knot spacing, the parameters haveequally spaced values (0, 1, 2, and so on) between edit points. The parametervalues of a uniform curve always range from 0 to the total number of spanson the curve. This is the default setting.

1 2 3 4

5

6

1 2 3 4 5 6

7

8



Multiple EndKnots

The joints where the curve spans are joined are called knots. Toggle MultipleEnd Knots on to help control the shape of the curve. The default is on.

For more information on editing curves, see:

• “Creating the perfect curve” on page 54.

• “Using the Curve Editing Tool” on page 84.

• “Editing curves in the Attribute Editor” on page 79 for information aboutediting the curve once you have created it.

Tip

Uniform knot spacing produces a curve with a more predictableparameterization. Chord knot spacing produces a better curvaturedistribution, and, when used to build surfaces, better texture mapping. See“What is parameterization?” on page 56 for more information about knotspacing.

Multiple End Knots toggled on Multiple End Knots toggled off

Notice how thecurve does notgo through theend CVs.


Creating curvesCreating curves with edit points

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Creating curves with edit pointsAn edit point is a point that controls the shape of a curve or surface. Use theEP Curve Tool to help define how many spans sit on the curve. Edit pointcurves are also useful if the curve must go through certain points.

When constructing a curve with edit points, the edit points are visible whilethe curve is being constructed. Unlike the CV method where you must placeseveral points to construct the curve, only two edit points are necessary tocreate the initial curve segment, no matter what degree of curve.

To create an edit point curve:

1 Select Curves → EP Curve Tool.

2 Click in any of the views to place the first edit point. A small letter x isdisplayed.

3 Click to place the second edit point. When you place the second edit point,you create a curve segment that interpolates the two edit points. Click toplace as many edit points as you want. As you plot each additional editpoint, a new curve segment is created.

4 To complete the curve so you can start to place new curve points, pressEnter.

The following shows a curve constructed with four edit points.

To create an edit point curve-on-surface:

1 Select the NURBS surface.

2 Click the Make Live icon on the Status Line (or select Modify → Make Live)to make the surface live.

3 Select Curves → EP Curve Tool and place the curve-on-surface pointsdirectly on the live surface.

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Changing the edit point curve shapeOnce an edit point curve is drawn, or while you are drawing it, you maywant to modify its shape.You can use the transformation tools to move,rotate, or scale edit points to change the shape of your curves.

To change the shape of the curve as you create it:

1 Before you complete the edit point curve, press the Insert key on thekeyboard. This displays a move manipulator which appears on the editpoint at the end of the curve by default.

2 Drag the manipulator to change the curve’s shape.

3 To continue to change the curve’s shape, click with the left mouse button toselect another edit point and drag the manipulator.

To change the shape of the curve after it is constructed:

1 Click the Select by component type icon.

2 Click the Parm Points icon to display the pop-up menu, then toggle EditPoints on.

or

While the pointer is over an active edit point curve, use the right mousebutton and drag to select Edit Point from the marking menu.

3 Click to select the edit point (or edit points) you want to move. Select atransformation tool (for example, the Move Tool), and drag the manipulatorto move the edit point.

Notes

You can only select one edit point at a time. This prevents the curve shapefrom changing too much.



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Setting EP Curve Tool optionsSet the tool options before you create the curve. To open the optionswindow, select Curves → EP Curve Tool - ❐.



Select a Curve Degree option to specify the curve degree.

1 Linear curves are often referred to as polylines (linear segments), degree 2curves as quadratics, 3 Cubic curves as cubics (the default), degree 5 asquintic, and degree 7 as heptic. The higher the curve degree, the more pointsyou need to define a single curve span. If the number of control points is thesame and the curve degree is high, the curve looks as though it has moretension than if the degree is low.



Changing the knot spacing

The type of knot spacing relates to the U parameter values assigned to editpoints (also referred to as parameterization). Select an option for KnotSpacing.

Chord length If you create a curve with Chord length knot spacing, the parameter valuedepends on the distance along the length of the curve. An initial parametervalue of 0 is assigned to the start of the curve, then the value is increasedproportionally to the chord length between edit points.

Uniform If you create a curve with Uniform knot spacing, the parameters haveequally spaced values (0, 1, 2, and so on) between edit points. The parametervalues of a uniform curve always range from 0 to the total number of spanson the curve. This is the default setting.





Tip

Uniform knot spacing produces a curve with a more predictableparameterization. Chord knot spacing produces a better curvaturedistribution, and, when used to build surfaces, better texture mapping.


Creating curvesCreating curves using a pencil

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Creating curves using a pencilUse the Curves → Pencil Curve Tool to sketch a curve, rather than create itby placing CVs or edit points.

To create a curve using a pencil:

Sometimes the most natural way to create a curve is to sketch it, rather thanplacing CVs or edit points. The pencil construction method lets you create acurve as easily as drawing a line on a piece of paper.

1 Select Curves → Pencil Curve Tool.

2 The pointer changes to a small pencil. Position it where you want the curveto begin.

3 Click-drag the pencil to sketch a curve.

4 To stop sketching, release the mouse button. The line is fit with a curve thathas chord length parameterization by default.

Sketching in different views

As the curve is sketched, the pencil position is sampled as often as possible.Points are kept if they are at least five screen pixels from the previous point.When the mouse button is released and the actual curve is fitted to thepoints, the curve interpolates the first and last point.

If you are sketching in an orthographic view (front, top, or side), two of thecoordinates of the spline correspond to those of the current view and theother coordinate is set to 0. If sketching in the perspective view, the curve iscreated on the ground plane or live surface.


Creating curvesCreating curves using a pencil

Setting Pencil Curve Tool optionsSet the tool options before you create the curve. To open the optionswindow, select Curves → Pencil Curve Tool - ❐.



Select a Curve Degree option to specify the curve degree. 1 Linear curvesare often referred to as polylines (linear segments), and degree 3 curves ascubics.





Warning!

Curves created using a pencil usually have many CVs. UseCurves→Rebuild Curves to smooth out and simplify this type of curve.


Creating curvesCreating a curve-on-surface

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Creating a curve-on-surfaceA curve on surface is a curve that you create directly on a surface. Thesespecial curves are created within the UV parameter space of a chosen surfaceand become part of that surface.

Creating trim curvesIn general, you draw a curve-on-surface to prepare a surface for trimming,or to create a curve to use in subsequent surface construction. You can dothis in various ways, including intersecting objects, creating fillets betweenobjects, or projecting curves onto a surface.

See “Trimming surfaces” on page 373 for more information on how to usethe Edit Surfaces → Trim Tool.

To create a curve-on-surface by placing it onto a live surface:

To draw a curve-on-surface, select the surface, then select Modify → MakeLive or click the Make Live icon from the Status Line. Use any curvecreation tool to draw the curve directly onto the surface.

NURBS plane “live” and draw a curve on the surface.Click the Make Live icon from the Status Line to make an active primitive

Trim curve

Trimmed surface



To create a curve-on-surface using a surface fillet:

1 In the Circular Fillet options window (Surfaces → Circular Fillet - ❐), toggleCreate Curve On Surface on.

2 Pick the surfaces you want to create a fillet between.

3 Select Edit Surfaces → Circular Fillet to create a fillet between the twosurfaces.

See “Creating trim curves” on page 261 in Chapter 7, “Filleting surfaces,” forinformation on filleting functions and their associated options.

To create a curve-on-surface by intersecting surfaces:

A curve-on-surface is created when you intersect surfaces using EditSurfaces → Intersect Surfaces.

See “Intersecting surfaces” on page 385 for more information about IntersectSurfaces and its options window.

Trim curves Trimmed surface

Trim curve Trimmed surface



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To create a curve-on-surface by projecting curves:

Use Edit Surfaces → Project Curve to project curves, such as NURBS text,onto a surface. The projected curves become trim curves.

See “Projecting curves” on page 390 for more information about ProjectCurve and its options window.

Trim curves Trimmed surface


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4 Editing Curves

This chapter includes information about editing curves. It also describessome of the tools you use to edit surfaces built from curves.

The following topics are discussed in this chapter:

• “Editing curves in the Attribute Editor” on page 79• “Using the Curve Editing Tool” on page 84• “Adjusting CVs” on page 90• “Inserting knots and isoparms” on page 93• “Extending curves” on page 100• “Offsetting curves and curves on surface” on page 107• “Fitting cubic geometry to linear geometry” on page 120• “Filleting curves” on page 123• “Opening and closing curves and surfaces” on page 133• “Duplicating curves and isoparms” on page 139• “Attaching curves and surfaces” on page 148• “Detaching curves and surfaces” on page 156• “Aligning curves and surfaces” on page 165• “Projecting curve tangents” on page 186• “Reversing the curve or surface direction” on page 195• “Rebuilding curves” on page 199“

Editing curves in the Attribute EditorTo edit completed curves and curve-related operations, use the AttributeEditor. The Attribute Editor for curves includes parameters that let youtransform the curve and validate the curve’s history, as well as change theway it is displayed.

First select the curve you want to edit. To open the Attribute Editor:

• Click the option box (❐) beside its name in the Object pop-up menu in theChannel Box.


Editing CurvesEditing curves in the Attribute Editor

• Select the active curve’s name from the marking menu.


• If the curve has history, you can open the Attribute Editor from the Historylist menu on the Status Line, or from the Inputs pop-up menu in the markingmenu.

Transforming curves in the Attribute EditorClick the curve tab to open the transformation sections of the editor.

Transform Attributes

Use the Transform Attributes section to enter values to move, rotate, scale,or shear the curve. You can also change the X, Y, Z rotation order or rotatethe local axes.



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Pivots

Use the Pivots section to scale or rotate the world space pivot, and toggle thedisplay of scale and rotate pivots on or off.

Limit Information

Use the Limit Information section to set limits to the transformations of thecurve. You toggle the Limit X, Y, or Z boxes on or off and then change thevalues in the transformation boxes. When you do this, you can only move,rotate, or scale to the unit value you set in the corresponding boxes.

Display

In the Display section, you can toggle the display of the local axis, display aselection handle, set a default manipulator (if you use the Show ManipulatorTool), or choose to hide the whole curve or toggle it into a template.

Accessing the curve’s historyClick the curveShape tab to open the section of the editor that includes thehistory for the curve shape.

Click the triangle beside a heading to open that section of the editor.



Nurbs Curve History

The Nurbs Curve History section of the editor lists information for the activecurve. This information is read-only. It simply provides you with the curve’screation data.

Components

The Components section is displayed when you select a CV on a curve thatis created without history. The parameter boxes list the position of any CVsselected on the curve. This information is also available from the ChannelBox.

Component Display

For curves created with CVs, the Component Display section lets youchange parameters to alter the curve’s display.

Channel Box

Attribute Editor



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You can also toggle the display of CVs, edit points, or hulls on or off, andturn off the display of the curve in the Object Display section.

Object Display

The Object Display section lets you toggle the visibility of the curve on oroff, or turn it into a templated or intermediate curve. For example, the curvebecomes invisible since it will only be used as a guide for subsequentoperations.

Bounding Box

The Bounding Box Information section is read-only. It displays the minimumand maximum world space coordinates of a curve along the X, Y and Z axes.


Editing CurvesUsing the Curve Editing Tool

Using the Curve Editing ToolOnce you create a curve, you can open the Channel Box or the AttributeEditor and transform it or change the way it displays. You can also changeits shape by transforming the CVs using the transformation tools.

The Curve Editing Tool (Curves → Curve Editing Tool) is a shortcut tool.Use it to quickly change the shape of a curve by manipulating the tangent orposition of a curve at any point along its length by scaling or rotating thetangent vector. This tool can be used on any modeling curve or animationmotion path.

To modify a curve using the curve editor manipulator handles:

1 Select Curves → Curve Editing Tool.

2 Click on the curve you want to modify to display the curve editormanipulator. It has several manipulator handles.

3 Click-drag an active manipulator to change a curve point position andtangent alignment.

Tips

The Curve Editing Tool will not modify the parameterization of the curve(chord or uniform). Use Curves → Rebuild Curves to do this.

If you display curve CVs (Display → NURBS Components → CVs) whileusing the curve editor manipulator, notice how the manipulator changesthe tangent by changing the position of the CVs of the curve.

Parameter Position

Point Position

Tangent Scale

Tangent Direction



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Changing the parameter positionThe parameter position handle of the manipulator determines on whichpoint on the curve the curve editor manipulator is acting. As you move italong the curve, it shows the tangent and scale directions of the curve at thatparameter value. Click-drag to slide the parameter position manipulatorhandle to a new position, or type a new value in the Numerical Input line,then press Enter.

Transforming the curve tangentsA curve tangent is the slope of the curve at a specific point. Click-drag themanipulators to interactively scale or rotate the curve tangents.

When using these manipulators, you can use either the right or middlemouse button to modify the curve tangents.

• Click-drag with the left mouse button to move an active manipulator.

• Click-drag with the middle mouse button to move an active manipulatorrelative to the mouse position.

Tips

If you use the middle mouse button to drag the manipulator all the way tothe left, it indicates the beginning or start point of the curve.

If Snap to points is on when you are using this manipulator, you can snapto edit points on the curve. Click the Snap to points icon on the Status Lineto turn snapping on.



In the following example, the Tangent Scale manipulator handle scales thetangent.

In this example, the Point Position manipulator handle changes the pointposition.

In this example, the Tangent Direction manipulator handle changes thetangent direction.

Tangent Scalemanipulator

Point Positionmanipulator

Tangent Directionmanipulator



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Aligning the tangent horizontally or verticallyThe red and blue dashed lines represent the AxisManips. Click once on adashed line to align the tangent either horizontally or vertically.

Click the red dashed line to align the tangent horizontally.

Click the blue dashed line to align the tangent vertically.


Editing CurvesAdding points to a curve

Adding points to a curveAfter a curve is constructed, you sometimes find that additional points arenecessary to move points on a curve.

Use the Curves → Add Points Tool to add additional CVs or edit points to acurve or curve-on-surface.

To add CVs to a curve:

If the curve is created with CVs:

1 Select Curves → Add Points Tool. The CVs are displayed.

2 Click on the curve to add a new CV. Continue clicking to add additionalpoints. The new curve segment is tacked down from where you added thepoint.

3 Keep clicking to add additional CVs.

To add edit points to a curve:

If the curve is created with edit points:

1 While the curve is active, click the Select by component type icon.

Tip

If you want to add points to the start of a curve, first select Curves →Reverse Curves to reverse the curve direction.

Select the Add Points Tool.

Click to add

Click to add

a new CV.

additional CVs.

CVs are displayed.


Editing CurvesAdding points to a curve

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2 With the right mouse button, click the Parm Points icon and toggle EditPoints on from the pop-up menu.

or

While the curve is active, use the right mouse button to select Edit Pointfrom the marking menu.

3 Select Curves → Add Points Tool.

4 Marquee-select the edit point at the end of the curve (the last edit pointplaced), then click to add a new edit point.

5 The new curve segment is tacked down from where you added the point.Keep clicking to add additional edit points.

Tip

Make sure the Points icon is not selected, otherwise CVs are selected first.


Editing CurvesAdjusting CVs

Adjusting CVsUse Curves → CV Hardness to turn multiplicity factors of CVs on or off. See“Setting Insert Knot and Insert Isoparm options” on page 96 for informationabout changing the multiplicity factors for curve points.

To increase or decrease the CV hardness:

1 While the curve is active, click the Select by component type icon.

2 With the right mouse button, click the Points icon and toggle CVs on fromthe pop-up menu.

or

While the curve is active, use the right mouse button to select ControlVertex from the marking menu.

3 Open the CV Hardness options window (Curves → CV Hardness - ❐) andclick to turn Multiplicity to Full or Off.

Note

CV hardness only works on curves of degree 3 (cubic).



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Setting the multiplicity to full or off

Multiplicity By default, when a cubic curve is created, the end CVs have a multiplicityfactor of 3 and the arcs in between have a multiplicity factor of 1. Thefollowing options let you change the Multiplicity factors, or turn them off.

To change the multiplicity of the interior CVs to go from 1 to 3, select Full.This is the default. To change a multiplicity factor from 1 to 3, there must beat least two CVs on each side of the CV being modified that have amultiplicity factor of 1.

To change the multiplicity of the interior CVs to go from 3 to 1, select Off.

Example: smoothing text

Select all the CVs and set Multiplicity to Off to quickly remove all themultiple knots on a cubic curve. The following example shows how text ismodified by setting the Multiplicity to Off in the options window.

1 In component CV mode, marquee-select the text to pick all CVs.

2 Set the Multiplicity option Off in the options window and click the Applybutton. Notice how the text loses its hard edges.

Keeping original geometry

Turn the Keep Originals option On to specify whether the original curves orsurfaces are retained after you change the multiplicity setting, and to accessthe Attribute Editor.

Editing the CV hardness in the Attribute EditorUse the Attribute Editor to edit the CV hardness once the operation iscomplete. Make sure Keep Original is on when you perform the operationto be able to access the Attribute Editor.



To open the Attribute Editor, either:





Input Curve The Input Curve information is read-only. It gives you access to the historyof the curve you changed. Click the arrow button to select the curve andopen its section of the editor.

Multiplicity Enter a value in the Multiplicity box, or use the slider to specify the numberof knots you want to insert when adjusting the CVs. See “Selecting thenumber of knots or isoparms” on page 97 for information about changingthe multiplicity factor.


Editing CurvesInserting knots and isoparms

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Inserting knots and isoparmsSometimes you need to add extra spans on curves or more isoparms on asurface so you can edit surfaces to your specifications.

Use Curves → Insert Knot to insert additional points on a curve withoutchanging the shape of the curve. Use Edit Surfaces → Insert Isoparms toinsert additional isoparms on a surface without changing the shape of thesurface.

To insert points on a curve:

1 While the curve is active, select Display → NURBS Components → CVs orEdit Points.

2 Click the Select by component type icon, click the Parm Points icon, andselect Curve Points from the pop-up menu.

or

While the curve is active, use the right mouse button to select Curve Pointfrom the marking menu.

3 Click on the curve where you want to insert a knot. A point is highlightedwhere you click.

4 To update the curve, select Curves → Insert Knot.



To insert isoparms on a surface:

1 While the surface is active, click the Select by component type icon.2 With the right mouse button, click the Lines icon and toggle Isoparms on

from the pop-up menu. You can also click the Parm Points icon, selectSurface Points, then click on a point on the surface.

orWhile the surface is active, use the right mouse button to select Isoparm orSurface Point from the marking menu

3 Click-drag an existing isoparm to where you want to add a new isoparm, orselect a point on the surface and click-drag, then select Edit Surfaces →Insert Isoparms to insert the new isoparm.

Tips

To change the location of the new knot before you insert it, hold the mousebutton and drag the highlighted point to where you want it. As thelocation of the knot changes, the parameter value on the Feedback Lineupdates to indicate the new position of the point on the curve.

You can select more than one curve point at a time. Press the Shift keywhile selecting the curve points then select Curves → Insert Knot.

Parm Points Lines



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Positioning knots or isoparms using the Channel Box

When you insert a knot, the Channel Box includes a Parameter box fromwhich you can enter values to change the position of the knot.

When you insert an isoparm, the Channel Box includes a Parameter box, aswell as a Direction pop-up menu.

Enter a value in the Parameter box to reposition the isoparm. With thepointer over the Direction box, use the left mouse button to insert theisoparm in U or V. A Direction pop-up menu is also available in theAttribute Editor.

Tip

Unlike a curve which has only a U parametric direction, a surface has botha U and a V parametric direction. If you are inserting a U directionalisoparm, you can only move along the V parametric direction on thesurface. If you are inserting a V directional isoparm, you can only movealong the U parametric direction on the surface. Look in the Feedback Lineto verify your selection.

You can select more than one isoparm at a time. Hold the Shift key whileselecting the isoparms then select Edit Surfaces → Insert Isoparms.



Setting Insert Knot and Insert Isoparm optionsTo open the options window, select Curves → Insert Knot - ❐ orEdit Surfaces → Insert Isoparms - ❐.

Multiplicity You can use the Multiplicity options to insert knots or isoparmsconcurrently or one-by-one.

Inserting knots or isoparms concurrently

Select Set to and continue inserting new knots into the curve or isoparms tothe surface until you achieve the specified multiplicity value. For example, ifmultiplicity at a point is 1 and the value in the Multiplicity box is set to 3,two knots are added to achieve a multiplicity of 3 on a CV curve.

See also, “Adjusting CVs” on page 90 for more information about turningthe multiplicity factors of CVs on or off.



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Inserting knots or isoparms one-by-one

Select Increase by to insert the number of knots specified in the Multiplicitybox.

Selecting the number of knots or isoparms

Enter a value in the Multiplicity box, or use the slider to specify the numberof knots you want to insert.


Toggle Keep Original on to determine whether the original curves orsurfaces are retained after the insertion, and to let you use the ShowManipulator Tool.

Note

These new knots do not change the shape of the curve or surface.

Set to 3

Click to inserta point and pressthe Insert button.

Notice theextra points.



Editing the inserted knot or isoparm position using manipulators

If Keep Original is toggled on and you select the Show Manipulator Toolbefore you insert a knot, a manipulator is displayed at the insert location.Drag this manipulator to reposition the knot.

If you select the Show Manipulator Tool before you insert an isoparm, theisoparm remains highlighted after the insert operation is performed. Thismeans you can drag the isoparm to a new location while the surface isactive.

See “Using the Show Manipulator Tool” on page 11 for more informationabout the Show Manipulator Tool and modeling functions.

Editing the insert in the Attribute EditorTo edit an active inserted knot or isoparm, use the Attribute Editor. To openthe Attribute Editor, either:







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Input Curve/Surface

The Input Curve or Input Surface information is read-only. It gives youaccess to the history of the curve or surface isoparm you used. Click thearrow button to select the curve or surface isoparm and open its section ofthe editor.

Add Knots The Add Knots toggle is the same as the Multiplicity toggle in the optionswindow. If toggled on, the number of knots you specify (in Number ofKnots below) are added. If toggled off, knots are added until the number ofknots you specified is achieved.

Parameter The Parameter section of the editor includes the value you set in the ChannelBox. This value is used to reposition the knot on the curve or the isoparm onthe surface. See “Positioning knots or isoparms using the Channel Box” onpage 95 for details.

Number ofKnots

The Number of Knots section lets you specify how many knots or isoparmsyou want to insert. This is the same as the Multiplicity option in the optionswindow.

Direction For isoparms, a Direction pop-up menu is available. Use this to insert theisoparm in U or V. You can also select an insert direction from the ChannelBox.


Editing CurvesExtending curves

Extending curvesSometimes after you construct a curve you find that it is not long enough tointersect other curves when using another operation (such as a Birail Tool),or that you want to use an extension of a particular curve to change a surface(such as a revolved object).

Use Curves → Extend Curve to extend a curve or curve-on-surface using alinear, circular, or extrapolation method.

To extend a curve:

The following example uses the default options — a linear extension at theend point of the curve. Change the options to extend curves to suit yourneeds.

1 Pick the curve you want to extend.

2 Select Curves → Extend Curve. By default, the extension occurs at the end ofthe curve at a unit distance of 1.0000.

To see the new points on the curve, select Display → NURBSComponents→ CVs or Edit Points. In the following example, notice theadded points where the curve extension occurs on the CV curve.

Note

If you extend a curve-on-surface the result will be a NURBS curve (a 3Dcurve instead of a 2D curve).

Extension



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Setting Extend Curve optionsTo open the options window, select Curves → Extend Curve -❐.

Changing the extension distance

Distance Distance is the default Extend Method. You can specify the length of theextension by entering a value in the Distance box below or using the slider.

To change the extension distance:

1 Select the curve and undo the previous extension.

2 Type a new value in the Distance box, then press the Extend button.

Note

For Linear extensions, the result is a linear distance. For Circularextensions, the result is an arc length distance. For Extrapolate extensions,the extension curve has an arc length equal to distance.



The following example shows what happens when you change the defaultdistance value on a curve that was used to create a revolved surface withconstruction history.

Press the Extend button to continue extending the curve by the distance youspecify.

Extending to a point location

Point Use the Point extend method to extend the curve to the current pointlocation. When you click the Point button, X, Y, and Z point extension boxesare displayed in the options window. By default, the extension occurs to theorigin (0, 0, 0).

To change the extension distance to or from the last point of the curve, selectthe curve. Enter a new value in the X, Y, or Z boxes, then press the Extendbutton.In the following, the extension occurs along the Y axis 10 units awayfrom the default pivot point location (at position 0, 10, 0 in world space).

Construction curve Default distance = 1

Distance changed to 3

Construction curve



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Changing the curve extension type

There are three types of curve extensions for the distance extension method:Linear, Circular, and Extrapolate.

If the curve is already extended, select it and undo the previous extension.Select an Extension Type button, then press the Extend button.

Linear The Linear extension type extends the curve in a straight line. This is thedefault.

Circular The Circular extension type extends the curve as an arc.

Extrapolate When you use Extrapolate, the extension maintains the tangent of theselected curve.

Specifying where to begin the extension

Extend Curve At Set Extend Curve At to Start or End to specify where the extension willoccur. The default is End.

For example, if you select the Start option, the curve is extended from thestart point of the curve.

To change where the extension begins:

Select an option for Extend Curve At, then click the Extend button.

The following shows a revolved surface with the construction curvehighlighted. Both End and Start methods are applied to the same curve.



Attaching and detaching the extension

Join to Original Toggle Join to Original on to attach the curve extension to the originalcurve. The default is on.

If toggled off, the curve extension is not attached to the input curve. Theinput curve and the curve extension are independent objects. You cantransform the resulting extension separately.

Simplifying the extension by removing multiple knots

Remove MultipleKnots

Toggle Remove Multiple Knots on to remove all multiple knots that arecreated when the curve is extended and Join To Original is on. Theresulting extended curve is of the same degree as the original curve.


If Keep Original is toggled off, the original curve is extended. If toggled on,a copy of the original curve with the extension is created. The default is off.

End method selectedConstruction curve

end

start

Start method selected

Join to Original on Join to Original off

Original curve



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Editing the extension using manipulators

If Keep Original is toggled on and you select the Show Manipulator Toolbefore extending a curve, manipulators are displayed on the curve and aDistance parameter box is displayed in the Channel Box.

In the following, dragging the manipulator changes the distance from thedefault 1.0 to 4.0. Notice the Distance value in the Channel Box.

Drag the manipulator to further extend the curve, or type a distance value inthe Channel Box. See “Using the Show Manipulator Tool” on page 11 formore information about the show manipulators.

Note

Be careful when you toggle Join to Original off. If both Keep Original andJoin to Original are toggled off, the extension curve replaces the originalcurve.



Editing the extension in the Attribute EditorTo edit an extended curve, use the Attribute Editor.






The options you set in the options window or the Channel Box aredisplayed. See the option descriptions for details. The Attribute Editor for acurve extension includes the following additional parameters:

Input Curve Input Curve information is read-only. It gives you access to the input curveyou extended. Click the arrow button to select the curve and open thatsection of the Attribute Editor.

Input Point If Point is selected as the Extend Method in the options window, the InputPoint parameter boxes are made available.


Editing CurvesOffsetting curves and curves on surface

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Offsetting curves and curves on surfaceUse Curves → Offset Curve to create a curve parallel to the original at aspecified offset distance.

Use Curves → Offset Curve On Surface to create a curve-on-surface parallelto the original curve-on-surface.

To offset a curve:

1 Select the curve you want to offset, then select Curves → Offset Curve.

2 An offset curve is created at a default offset distance of 1.0.

3 To change the default offset distance interactively, select the ShowManipulator Tool to display a LengthPoint manipulator on the originalcurve.

4 Click-drag the manipulator to change the offset curve distance.

You can also change the offset distance from the options window, theAttribute Editor, or the Channel Box.

To offset a surface isoparm:

1 To select the surface isoparm you want to offset, click the Select bycomponent type icon.

2 With the right mouse button, click the Lines icon and toggle Isoparms onfrom the pop-up menu.

Original curve Offset Curve selected



or

While the surface is active, use the right mouse button to select Isoparmfrom the marking menu.

3 Click the isoparm you want to offset.

4 Select Curves → Offset Curve. The isoparm is offset by the default offsetdistance of 1.0.

If you want, you can now use this isoparm to create a beveled edge to thecylinder.

5 While the offset curve is highlighted, select Surfaces → Bevel.



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Change the offset distance from the options window, Attribute Editor, or theChannel Box. The following shows how to change the offset distance fromthe Channel Box.

6 To select the offset surface isoparm, open the Outliner or Hypergraphwindow (Window → Outliner or Hypergraph).

7 Click the heading for the offset curve in the Channel Box and enter a newDistance value for the offset.



To offset a curve-on-surface:

1 Draw a curve-on-surface, or use another method to create a curve-on-surface(see “Creating a curve-on-surface” on page 75 for details). In this example,the surface is live and the curve-on-surface is drawn in the top view.

2 Select Curves → Offset Curve On Surface while the curve-on-surface isactive. The curve-on-surface is offset by a default offset distance value of 1.0.

3 To change the default offset distance interactively, select the ShowManipulator Tool while the offset curve-on-surface is highlighted. Drag themanipulator, or enter a value in the Distance box in the Channel Box.

perspective viewtop view



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You can now use the Trim Tool (Edit Surfaces → Trim Tool), for example,to trim these sections out of the surface.



Setting Offset Curve optionsSelect Curves → Offset Curve - ❐ to open the options window.

Determining the normal direction

Use the Normal Direction options to specify how the offset is calculated.

Active View Active View calculates the offset relative to the original geometry in theactive view. Curves are offset in the plane of the active view.

GeometryAverage

Geometry Average calculates the offset using a geometry average. This isthe default.



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Changing the offset distance

The Offset Distance value is used to specify the distance between theoriginal curve and the offset curve. You can use manipulators and theChannel Box to change the distance between the original curve and the offsetcurve; you can also change this value in the Offset Distance box or move theslider to obtain the desired offset distance.

Connecting offset curve breaks

Breaks can occur in an offset if you attempt to offset a curve with CVs thathave a multiplicity greater than 1 or multiple knots. These curves can havesharp corners and the offset curve may therefore break apart at these points.

Connect Breaks The following Connect Breaks options are used to specify how breaks in anoffset curve can be adjusted.

Use Circular to insert circular arcs between the offset components.

Use Linear to connect the offset geometry linearly.

If Off is selected, the offset curve remains broken and no action is taken toconnect the offset geometry.

Tip

Planar curves are offset in the plane of that curve. 3D curves are offset in3D. If the original geometry is rotated out of the main planes orconstruction planes, you can get unexpected results when you create anoffset using the Active View normal direction. If this happens, delete theoffset geometry and create it again using the Geometry Averagecalculation.

Note

When Connect Breaks is set to Circular or Linear, multiple knots areinserted on the curve to preserve the curve shape. Any adjustment made tothe curve later in the vicinity of the multiple knot locations may result intangent breaks along the curve.



Curve loop cutting

Loop Cutting Turn Loop Cutting to On or Off to determine whether or not any resultingloops in the offset geometry are trimmed away. Loop Cutting is set to On bydefault.

Offset geometry looping occurs if the offset distance from the original curveexceeds the minimum bend radius (curvature) of the curve being offset. Forexample, if a curve has a 20mm radius and you try to offset more than 20mminward, the offset curve crosses over itself and creates a loop.

Setting the cutting radius

Cutting Radius When Loop Cutting is on (the default), the Cutting Radius value is used. Ifthe Cutting Radius value is greater than 0, instead of getting a sharp cornerat the point where the loop has been cut, the result is a small arc of the givenradius.

Loop Cutting onLoop Cutting off

Cutting Radius Cutting Radiusis 0.375is 0.0



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Subdividing offset geometry

MaxSubdivisionDensity

The Max Subdivision Density value is a multiplicative factor that specifiesthe maximum number of times the offset geometry can be subdivided withinthe current tolerance. The default is 5, which means any single span on thecurve could be subdivided up to 5 times.

Applying tolerance globally or locally

Use Tolerance With Use Tolerance, you can select to apply tolerance globally or locally.

If you select Global tolerance, the Positional value you set in Options →General Preferences → Modeling to calculate the tolerance is used.

If you select Local tolerance, a box displays where you can enter a new valueto override the Positional tolerance value you set in Modeling Preferences.

Local tolerance is useful where you want to change these values often, butdon’t want to change the Global tolerance all the time.

Note

A few functions include Use Tolerance as a construction operationalternative. For example, you can create a revolved surface with a presetnumber of spans, or you can toggle Use Tolerance on so that the revolvedsurface is closer to the actual surface of revolution.



Using tolerance values to place the offset curve accurately

Tolerance The Tolerance value represents the accuracy in which the offset curve isplaced at a specified distance. The default is accurate to within 0.05 units.The default unit is in centimeters. Offsetting is an iterative process thatcontinues until the current offset comes within the tolerance value or themaximum subdivision limit is reached.

Setting the curve range

Curve Range If you select Complete as the Curve Range, an offset curve is created alongthe entire original curve.

Select Partial to create an offset curve on only part of the original curve. Thiscreates a subCurve history node (initially set to the whole curve) which canbe edited using the Show Manipulator Tool.

Editing part of an offset curve

If Partial is the selected Curve Range in the options window, the parameterrange of an offset curve with history can be edited with manipulators.

1 Select the Show Manipulator Tool, then click on the offset curve result to listthe subCurve history node in the Channel Box.

2 To display the manipulators, click the heading in the Channel Box to selectthe subCurve history node. Notice how the original curve turns a gray color.

Drag the manipulators to edit the subCurve interactively, or enter values inthe Min Value and Max Value boxes in the Channel Box.



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Use the same procedure to edit part of an offset curve-on-surface or surfaceisoparm.

Setting Offset Curve On Surface optionsSelect Curves → Offset Curve On Surface - ❐ to open the options window.

Most of the options in this options window are the same as the options forOffset Curve. See “Setting Offset Curve options” on page 112 for details. Thefollowing describes the one option particular to Offset Curve On Surface.

Checking the offset’s tolerance accuracy

You can change the default value of Checkpoints Density to adjust thenumber of points per span at which the offset curve-on-surface is comparedwith the original. This lets you check if the offset curve is accurate to therequired tolerance.

Editing the offset curves in the Attribute EditorTo edit the attributes for a completed offset curve or curve-on-surface, usethe Attribute Editor. To open the Attribute Editor, either:







The Attribute Editor for an offset curve contains the attributes for the type ofinput you used to create the offset.The options you set in the optionswindow or the Channel Box are displayed. See the option descriptions fordetails.

Input Curve The Input Curve information is read-only. It gives you access to the historyof the curves or isoparms you used. Click the arrow buttons to select theinput curve or surface isoparm and open its section of the editor.



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Editing offset curves-on-surface in the Attribute Editor

The Attribute Editor for offset curves-on-surface differs slightly. Someattributes are not available for an offset curve-on-surface.

Editing subCurves in the Attribute Editor

If the Partial option is set as the Curve Range in the options window, theInput Curve box displays the subCurve history node. Click the arrow toaccess the subCurve and its Attribute Editor. See “Editing subCurves in theAttribute Editor” on page 19 for details.


Editing CurvesFitting cubic geometry to linear geometry

Fitting cubic geometry to linear geometryUse Curves → Fit B-Spline to fit a cubic curve to a degree 1 (linear) curve.

To fit a cubic curve:

1 Select the curve or curves to which you want to fit a cubic curve.

2 Select Curves → Fit B-Spline.

The fit is based on the tolerance type you select from the options window.

Tip

Typically you use Fit B-spline when importing curves and surfaces fromother systems that may import to Maya as degree 1 (linear) geometry.Degree 1 geometry is also quite common when working with digitizeddata.



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Setting Fit B-Spline optionsSelect Curves → Fit B-Spline - ❐ to open the options window.

Setting the tolerance

Use Tolerance The tolerance determines the degree of accuracy that is maintained betweenthe original and fit or interpolated curves. Select a Use Tolerance option toapply tolerance globally or locally.

If set to Global, the fit should be accurate to within 0.010 units. A unit refersto the current unit of linear measure (the default unit of measure iscentimeter). The default for Use Tolerance is Global.

If set to Local, you can change the default tolerance value in the PositionalTolerance box.



Editing the B-Spline curve in the Attribute EditorTo edit a fit b-spline curve, use the Attribute Editor.






Input Curve The Input Curve information is read-only. It gives you access to the originalcurve you used. Click the arrow button to select the curve and open itssection of the editor.

Tolerance The Tolerance value you set in the options window is displayed. See theoption descriptions for details.


Editing CurvesFilleting curves

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Filleting curvesUse Curves → Fillet Curve to create a circular bridge between two NURBScurves or two curves on surface.

There are two ways to construct curve fillets: Circular and Freeform. Selectthe type you want from the options window before you create the fillet.Circular is the default fillet construction type.

Creating circular curve filletsUse circular curve fillets to create curves with the exact amount of roundnessyou want. The curves do not necessarily have to intersect.

To create a circular curve fillet:

1 Marquee-select two curves.

2 Open the Fillet Curve options window (Curves → Fillet Curve - ❐). Makesure Circular (which is the default) is the selected Construction type.

3 Select Curves → Fillet Curve to create the curve fillet, or click the Filletbutton in the options window.

Tips

If you select more than two curves, the last two selected curves are used tocreate the fillet curve.

If creating a circular fillet, make sure the curves are on the ground plane orthe same construction plane.

You cannot fillet between a NURBS curve and a curve-on-surface, orbetween two curves on surface on different surfaces. If you do, a fillet iscreated on the first selected curve between its end points.


Editing CurvesCreating circular curve fillets

Editing the circular curve fillet with manipulators

1 Select the Show Manipulator Tool and click the filletCurve heading in theChannel Box to display the TopPoint manipulator and two parammanipulators for the fillet curve.

2 Click-drag the TopPoint manipulator to adjust the radius of the circularfillet.

Circular curve fillet

Param manipulators

TopPoint manipulator


Editing CurvesCreating circular curve fillets

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3 Click-drag the param manipulators to interactively slide the fillet curvealong the input curves.

4 In the following example, notice how the values update in the Channel Boxwhen all three manipulators are adjusted.

As you drag a manipulator, the parameter values are also updated in theFeedback Line. If you want, you can enter a numerical value in theNumerical Input line when a manipulator is active.


Editing CurvesCreating freeform curve fillets

Creating freeform curve filletsUse this type of filleting when you want more flexibility in choosing wherethe fillet occurs. You can specify exact parameter repositioning, or choose tofillet the curve wherever you need to.

To create a freeform curve fillet:

1 Make sure Freeform is the selected Construction type in the optionswindow.

2 Marquee-select the curves you want to create a fillet between.

3 Select Fillet Curve to create the curve fillet.

Editing the freeform curve fillet with manipulators

1 Select the Show Manipulator Tool and click the filletCurve heading in theChannel Box to display two param manipulators for the fillet curve.

2 Click-drag the param manipulators to interactively slide the fillet curvealong the input curves. Since the fillet curve is not circular, you can drag inany direction.



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As you drag a manipulator, notice how the parameter values change in theChannel Box and the Feedback Line and how the freeform fillet curve isadjusted. You can also type a numerical value in the Numerical Input linewhen a manipulator is active.



Setting Fillet Curve optionsSelect Curves → Fillet Curve - ❐ to open the options window.

Creating and attaching trimmed fillet curves

Trim If Trim is toggled on, the curves selected as the filleting components areautomatically trimmed back to the ends of the fillet curve.

Join The Join toggle is only available when Trim is toggled on. Use this option tojoin the trimmed curves to the fillet curve.

Freeform fillet with Trim toggled off. Same fillet with Trim toggled on.



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This toggle is only available if the Trim option is toggled on.

If Keep Original is toggled on, the original curves that you used to createthe fillet are retained. This lets you modify the geometry of the input curvesand recreate the fillet.

The following shows the same fillet with Trim, Join, and Keep Originaltoggled on.

Setting the fillet construction type

Circular Select Circular to create fillets with true radii, based on the current Radiusvalue. See “To create a circular curve fillet:” on page 123 for moreinformation.

Freeform Select Freeform when you need a fillet that is more flexible and less precise.Use this construction method to determine the contact points of the fillet andbase components. See “To create a freeform curve fillet:” on page 126 formore information.

Note

The Radius option is not available when you select the Freeform filletconstruction type.

When Join istoggled off, thetrimmed curves

When toggled on,both the trimmedcurves and the fillet

are not joined tothe fillet curve.

curve are joined.



Changing the fillet radius

The value you enter in the Radius box specifies the radius of the fillet forcircular curve fillet construction before the fillet is created. Use the slider orenter a new value, then press the Fillet button in the options window.

The radius can also be changed interactively using manipulators (if theShow Manipulator Tool is selected), from the Channel Box, or from thefillet’s Attribute Editor.

Selecting the free-form fillet type

The following Freeform Type options are used to specify on which side of acurve a free-form fillet is constructed.

Tangent If Tangent is selected, the fillet is pulled toward the intersection of thetangents of the two curves at the contact points.

Blend If Blend is selected, the fillet is pulled toward the mid-point of the projectedcontact points of the two curves. Each contact point is projected onto thetangent of the other curve. The default Freeform Type is Blend.

Blend Control Use Blend Control to adjust the fillet component. It can be toggled on or offwhen you use either filleting construction type. If toggled on, Depth andBias boxes are displayed.

Changing the fillet depth and bias

Depth The Depth value controls how much the fillet curve is pulled toward theintersection of the two curves.

Note

If Blend Control is toggled on when constructing circular fillets, theresulting fillet will not be truly circular. The true contact points from thecircular fillet are used to create a freeform fillet.



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Bias The Bias value controls how much the fillet curve is pulled to either of thetwo curves. See the following examples.

Editing curve fillets in the Attribute EditorTo edit a completed curve fillet, use the Attribute Editor.






The Attribute Editor for circular curve fillets and freeform curve filletscontain the same attributes. All other options are included in the Fillet Curveoptions window. See “Setting Fillet Curve options” on page 128 for details.

Depth = 0.5000Bias = 0.0000

Depth = 0.0000Bias = 0.5000

Depth = 0.3500Bias = 0.3500

Depth = 0.7500Bias = 0.1000

(default)



Input Curve The Input Curve information is read-only. It gives you access to the historyof the curves you used to create the fillet. Click the arrow buttons to selectone of these curves if you want to edit it.

CurveParameters

The Curve Parameter1 and Curve Parameter2 values correspond to thefillet’s param manipulators you see when the Show Manipulator Tool isselected. These parameter values define the region between the two curveswhere the fillet curve is created.


Editing CurvesOpening and closing curves and surfaces

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Opening and closing curves and surfacesUse Curves → Open/Close or Edit Surfaces → Open/Close to toggle curvesand surfaces open or closed.

To close an open curve:

1 Select the curve you want to close, then select Curves → Open/Close.

2 Select Curves → Open/Close again to re-open the curve.

To create a closed surface from an open curve:

1 Use an open curve as a construction curve and select Surfaces → Revolve.

2 Pick the construction curve and select Curves → Open/Close. The revolvedsurface is now closed.



3 You can open it again by selecting the construction curve and clickingCurves → Open/Close.

To open a closed surface:

1 Select the surface you want to open.

2 Select Edit Surfaces → Open/Close.

3 To close the open surface, simply select Edit Surfaces → Open/Close totoggle the surface closed.



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Setting Close Curve optionsSelect Curves → Open/Close Curves - ❐ to open the options window.

Preserving the shape of the original curve or surface

Use Preserve Shape to determine how the original curve or surface isaffected by the Open/Close operation. This option is toggled on by default.

Control points are added or deleted as necessary to preserve the shape of theoriginal curve or surface. If toggled off, the selected curve or surface is openor closed without ensuring that the shape of the original is preserved.

Keeping the original geometry

Toggle Keep Original on to determine whether the original curves orsurfaces are retained after Open/Close is performed.

Setting Close Surface optionsSelect Edit Surfaces → Open/Close Surfaces - ❐ to open the optionswindow.



Changing the surface direction

SurfaceDirection

The Surface Direction options, U, V, and Both, let you choose in whichdirection a surface is opened or closed. The following shows how theseoptions are used to close a beveled curve.

Selecting an isoparm to change the close direction

You can specifically select in which direction you want to close a surfacefrom the options window, or you can click to select isoparms on the surface.When you do this, you override the Surface Direction setting in the optionswindow.

To select isoparms on an open surface:



or

While the surface is active, use the right mouse button to select Isoparmfrom the marking menu.

3 Click on an isoparm in the direction in which you want it to open or close.

U V Both



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Editing the closed shape in the Attribute EditorTo edit the opened or closed curve or surface, use the Attribute Editor. Toopen the Attribute Editor, either:





U V U/V



The Attribute Editor for a closed curve contains the same attributes forcurves. See “Editing curves in the Attribute Editor” on page 79 for details.

For a closed surface, the options you set in the options window or theChannel Box are displayed. See the option descriptions for details.


Editing CurvesDuplicating curves and isoparms

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Duplicating curves and isoparmsUse Curves → Duplicate Curves to transform a curve-on-surface, aboundary curve, or an interior isoparm of an existing surface into a 3Dcurve.

To duplicate a surface isoparm:

1 Select the surface on which you want to duplicate an isoparm.



or

While the surface is active, use the right mouse to select Isoparm from themarking menu.

4 Click on a surface isoparm that is going in the same direction as the one youwant to duplicate.

5 Click-drag the isoparm to the required location, then release the mousebutton.



6 Select Curves → Duplicate Curves.

7 The selected surface isoparm is duplicated and highlighted, indicating that itis active.

Open the Hypergraph (Window → Hypergraph) to see the new duplicatedcurve.

Changing a duplicated isoparm’s direction

While the duplicated isoparm is active, use the left mouse button to selecteither U or V as the Isoparm Direction in the Channel Box or in thecurveFromSurfaceIso section of the Attribute Editor. U is the defaultdirection.

New 3D curve



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To duplicate a curve-on-surface:

The following shows how to duplicate projected text to create a text stringwhich follows the curve of a NURBS sphere.

1 Create and scale a NURBS sphere larger than the default.

2 Use Primitives → Create Text to create text and scale it larger than thedefault size. See “Creating and editing text” on page 235 for moreinformation.

3 Marquee-select the sphere and the text, then use Edit Surfaces → ProjectCurve to project the text onto the sphere. See “Projecting curves” on page390 for more information.

Notes and Tips

All transformations of the surface where the original curve is located arecombined and applied directly to the CVs of the new duplicated curve.This places the duplicate in the same location in space as the original.

If the surface isoparm you want to duplicate is either a U or V directionalisoparm, you can only move it along the U or V parametric direction on thesurface.



4 Select Curves → Duplicate Curves and use the Move Tool to move theduplicated text off the sphere.

To duplicate curves for trimming:

Another way you can use duplicate curves on surface is to trim holes fromboth sides of a surface using the same curve. The following shows how totrim holes out of a NURBS cylinder.

1 Create a primitive cylinder at the origin and scale it by 5 in X, Y, and Z.

2 Select the cylinder and select Modify → Make Live to make it a live surface.

3 In the front view, draw a curve on the cylinder (a curve-on-surface). Thiscurve must be a closed curve, so make sure the end points of the curve meet.To close the curve, you can also select the curve, then selectCurves → Open/Close Curves.



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4 Deselect the curve and select Modify → Make Live again to deselect thesurface. The curve you just created is highlighted.

5 Select Curves → Duplicate Curves. The curve is duplicated and appears inthe lead object color.

6 Click the Snap to grids icon on the Status Line.

7 In the top view use the Move Tool and click-drag to move the duplicatedcurve to the other side of the surface and rotate it in Y by -180.

8 To move the duplicated curve back onto the cylinder, enter 0, 0, 0 in theTranslate X, Y, and Z boxes in the Channel Box or in the Attribute Editor.

9 Select the cylinder and the duplicated curve, then selectEdit Surfaces → Project Curves to highlight the projected curve.



10 Click to deselect everything. Select Edit Surfaces → Trim Tool, then click onthe cylinder as the area to keep. Press Enter to trim the holes out of thesurface.

Tip on duplicating a curve-on-surface

If you move a curve-on-surface over a surface, it does not necessarily staythe same shape. For example, if you create a circular curve-on-surface andthen start sliding it to a region of the surface where the isoparms are closertogether, the curve-on-surface becomes squashed and oval shaped.



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To keep the same shape, duplicate the curve-on-surface to make it into a 3Dcurve. Move it over the surface to place it where you want. You can thenproject it back onto the surface to create a curve-on-surface and retain thecurve’s shape.

Editing part of a duplicated curve

1 While the duplicated curve is active, select the Show Manipulator Tool. Clickthe heading in the Channel Box to display the manipulators.

2 Drag the manipulators or enter Min or Max values to edit the duplicatedsurface isoparm.



Setting Duplicate Curves optionsSelect Curves → Duplicate Curves - ❐ to open the options window.

Grouping the original curve on or off

The Group With Original option is toggled off by default. If you duplicate acurve with Group With Original toggled off, the resulting duplicated curveuses the world space version of the surface and is created with the initialsurface’s transformation.

If toggled on, the resulting curve uses the local space version of the surface,but is parented under the surface transformation.

It may look the same as the isoparm or curve-on-surface, but if you edit theCVs on the resulting curve or apply any kind of transformation to it, youwill notice a difference, especially after any subsequent surfacetransformations.

For example, duplicate a cylinder isoparm, move the middle CV of theresulting curve in X, then rotate the cylinder 90 degrees about Z. If theoption was toggled on, the center CV of the curve is moved in X. If toggledoff, the center CV is moved in Y, which may be the result you need.



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Editing the duplicated curve in the Attribute EditorTo edit a duplicated curve, use the Attribute Editor. To open the AttributeEditor, either:





A duplicated curve includes the same options and parameters for a curve.See “Editing curves in the Attribute Editor” on page 79 for details.


Editing CurvesAttaching curves and surfaces

Attaching curves and surfacesYou use Curves → Attach Curves to join two curves by attaching theirendpoints to create a single curve. You can also join two surfaces byattaching their edges to create a single surface.

Attaching curves and surfaces with history offThe Attach options windows (both for curves and surfaces) contain a togglethat lets you keep the original curves or surfaces after the attach isperformed. Keep Original is toggled on by default. Try not to toggle thisoption off if history is set to on (the Construction History icon in the StatusLine); odd behavior can occur if the attached curve or surface is modifiedlater.

In the following, two curves are attached using different settings for KeepOriginal and history. They are then scaled by 0.5 in X, Y, and Z.

If history is on and Keep Original is toggled off, the attached curve replacesthe first curve. When you scale the resulting attached curve, the scale isapplied to the original curve (the one that was replaced) and changes theshape of the curve, thereby changing the attachment.

Original curves

The attachment looks fine,but when you scale theattached curve, the resultsare probably not what youexpected.

History on, Keep Original off



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If you want to scale the attached curve and maintain its shape, make sureconstruction history is off when Keep Original is toggled off, or bothconstruction history and Keep Original are set to on.

To attach two curves:

1 Marquee-select the curves you want to attach.

2 Select Curves → Attach Curves to attach the two curves. The curve ends thatare closest to each other are attached.

You can also place a curve point to specify the attach location. To place acurve point, use the marking menu or the Select by component type icon.

To place a curve point using the marking menu:

1 Select the first curve, press the right mouse button while the pointer is overthe curve and select Curve Point from the marking menu.

History on, Keep Original on

History off, Keep Original off



2 Click on the curve where you want to place the first curve point. A point isdisplayed at the click location.

3 Shift-select the other curve and release the mouse button.

4 Press the right mouse button while the pointer is over this curve and selectCurve Point from the marking menu again.

5 Shift-select and click at the next attach location. Another point is displayedat the click location.

6 Select Curves → Attach Curves to attach the curves.



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To place a curve point in component mode:

1 Click the Select by component type icon on the Status Line.

2 With the right mouse button, click the Parm Points icon and toggle CurvePoints on from the pop-up menu.

3 Click on the first curve to place the first point and Shift-click on the secondcurve. Points are displayed at each click location.

4 Select Curves → Attach Curves to attach the two curves.

5 To return to object selection mode, click the Select by object type icon on theStatus Line.

To attach two surfaces:

To specify the attach location for surfaces, use the marking menu or theSelect by component type icon. To attach two surfaces, you must selectsurface isoparms.

Important Note

When you select isoparms to attach surfaces, the surfaces are attacheddepending on the selection order. In the following example, the isoparms areselected in a different order. Notice the difference between the two resultingsurfaces. The same applies when attaching two curves.



To select isoparms using the marking menu:

1 With the pointer positioned over the surface, use the right mouse button toselect Isoparm from the marking menu, and click to select an isoparm.

2 Shift-select the other surface and release the mouse button.

Pick first

Pick first

Selectisoparm



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3 With the pointer positioned over this surface, use the right mouse button toselect Isoparm from the marking menu again.

4 Shift-select the second isoparm.

5 To attach the surfaces, select Edit Surfaces → Attach Surfaces.

To select isoparms in component mode:

1 Click the Select by component type icon on the Status Line.


3 Click on the first isoparm you want to attach, then Shift-select the secondisoparm.

4 Select Edit Surfaces → Attach Surfaces to attach the two surfaces.

5 To return to object selection mode, click the Select by object type icon on theStatus Line.



Setting Attach Curves and Attach Surfaces optionsSelect Curves → Attach Curves - ❐ or Edit Surfaces → Attach Surfaces - ❐to open the options window.

Keeping and removing knots

Multiple Knots The Multiple Knots options are used to specify whether the multiple knotsat the join point are kept or removed after the attach is done.

Use Keep to keep the multiple knots created at the join point as a result ofthe attach. This is the default.

Use Remove to remove the multiple knots at the join point. The shape of thegeometry can be changed if required.



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If Keep Original is toggled on, the original curves or surfaces are retainedafter the attach is performed. See “Attaching curves and surfaces withhistory off” on page 148 for information.

Editing the attachment in the Attribute EditorYou can edit the parameters displayed in the Channel Box and the AttributeEditor for a selected attached curve or attached surface node.






The options you set in the options window or the Channel Box are displayedin the Attribute Editor. See the option descriptions for details.

These parameters are the same as the Curves → Align Curves parameters.All Continuity and Scaling options are off by default and should not betoggled on. The Join parameter can be changed to specify a different end ofthe curve or surface isoparm to use in the attach.

See “Editing the alignment using manipulators and the Channel Box” onpage 178 and “Editing the alignment in the Attribute Editor” on page 180 formore information about these parameters.

Tip

If you construct the initial curves or surfaces carefully, an attach usuallyproduces the desired results without knot insertion. If you perform anattach operation with Multiple Knots set to Remove and then feel youneed more localized control, you can reverse it using Edit → Undo, thenperform the Attach again with Keep selected.


Editing CurvesDetaching curves and surfaces

Detaching curves and surfacesUse Curves → Detach Curves or Edit Surfaces → Detach Surfaces to breaka curve into two curves, to open a currently closed curve, or to detach asurface.

To detach a curve:

The following shows what happens when you detach part of theconstruction curve used to create a revolved surface. The revolved surfacemust be created with the Construction History icon on.

1 Select the original construction curve.

If it is difficult to select the construction curve, open the Hypergraph orOutliner window and select it from there.



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3 With the right mouse button, click the Parm Points icon and toggle CurvePoints on from the pop-up menu.

or

While the pointer is over the active curve, use the right mouse button toselect Curve Point from the marking menu.

4 Click where you want to detach the curve. A point appears where you click.This point is the parameter value.

5 Select Curves → Detach Curves. The construction curve is detached at thisparameter value, the detached section of the curve is highlighted, and therevolved surface is reconstructed.

Tip

To change the detach location before detaching the curve, click on anotherpoint and drag it along the curve.



6 To delete the unwanted curve section, deselect everything, select the part ofthe curve you want to delete and press the Backspace key.

You can also detach at more than one curve point at a time. Shift-click whenplacing the curve points and select Curves → Detach Curves.

To move a periodic curve’s start point:

A periodic curve, such as a NURBS circle or a closed curve, has a start point.You can move this start point using Detach Curves.

1 Make sure the Construction History icon is off in the Status Line before youcreate the curve.

2 With the right mouse button, select Curve Point from the marking menu.

3 Click to determine a detach point, then select Curves → Detach Curves. Thismoves the start point to the curve point position.



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1 Select the surface you want to detach.



or

While the pointer is over the active surface, use the right mouse button toselect Isoparm from the marking menu.

4 Click on the isoparm where you want to detach the surface.

start pointdetach point

start point moved



5 Select Edit Surfaces → Detach Surfaces. The surface is detached from theisoparm location you specified.

6 You can now transform the detached section of the surface.

You can also detach at more than one isoparm at a time. When you select theisoparms, Shift-click to select more than one isoparm, then selectEdit Surfaces → Detach Surfaces.



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Setting Detach Curves and Detach Surfaces optionsSelect Curves → Detach Curves - ❐ or Edit Surfaces → Detach Surfaces - ❐to open the options window.


If Keep Original is toggled on when you perform the detach, the originalcurve or surface is retained. If you use the Show Manipulator Tool when youperform the detach, a detach curve manipulator is displayed. Thismanipulator lets you interactively change the parameter value for thedetach.



If you later want to change this value with the Show Manipulator Tool,select the detached curve, then select the detach curve node in the ChannelBox, and enter a new parameter value.

Editing the detachment in the Attribute EditorThe Attribute Editor for a detached curve contains the same attributes forcurves. See “Editing curves in the Attribute Editor” on page 79 for details.






The Attribute Editor for detached surfaces, however, contains the sameattributes you find in the Channel Box. See “Changing the detach directionand position,” that follows for details.



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Input Surface The Input Surface information is read-only. It gives you access to the historyof the surface you detached. Click the arrow button to select the surface andopen its section of the editor.

Direction Use the Direction pop-up menu items to specify the direction of thedetachment.

Keeping the geometry in U or V

The Keep section lets you specify whether or not original geometry is keptin either U or V when you perform the detachment.

Changing the detach direction and position

You can change the direction of the detachment by selecting U or V from theDirection pop-up menu in the Channel Box or Attribute Editor. You can alsoenter a parameter value to change where the detachment occurs.

In the following, a V isoparm is selected, moved, and then detached twice.The first detachment moves the seam of the cone, which is periodic in V.



If you change the parameter value, the detachment area is increased ordecreased. In the following example, the parameter value is increased to 1.5.

To change the detach direction, select U from the Direction pop-up menu todetach the isoparm from a parameter value of 1.5 in the U direction.


Editing CurvesAligning curves and surfaces

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Aligning curves and surfacesUse Curves → Align Curves and Edit Surfaces → Align Surfaces toestablish continuity between curves and surfaces.

What is continuity?Continuity between curves or surfaces can be an important factor when youwant to create the perfect surface for animation and rendering purposes.

Aligning always enforces at least positional continuity, and lets you enforcetangent and curvature continuity. Once the selected elements are aligned,you can adjust the tangent magnitude at the junction of the two elements bysetting options or manipulators to give you more control when modifyingthe aligned elements.

When you use Align, the selected elements are modified to positionalcontinuity based on one option setting, then modified to tangent continuitybased on a second option setting. See “Setting Align options” on page 172for more information.

Positional continuity alignsthe first CVs along the

Tangent continuity usesthe second CVs to achievetangent continuity.

Curvature continuity usesthe third CVs to achievecurvature continuity.

curves or surface isoparms.

1st CV2nd CV

3rd CV

1st CV



Selecting curve points and isoparms to alignAlign doesn’t always work when you marquee-select curves or surfaces.Select a component (a curve point or a surface isoparm) to reliably definewhich ends to align.

Aligning CurvesTo specify the align location for curves, you have to place curve points. Usethe Select by component type icon or the marking menu.

The following alignment is performed using the default option settings.

To align two curves in component mode:


2 With the right mouse button, click the Parm Points icon to toggle CurvePoints on from the pop-up menu.

3 Click on the first curve to place the first point, and Shift-click on the secondcurve. Points are displayed at each click location.

4 Select Curves → Align Curves to align the two curves.

Important notes

The Align options windows (both for curves and surfaces) contain anAttach toggle that lets you attach the original curves or surfaces after thealign is performed. Attach is toggled off by default. If this option is on,toggle history off (the Construction History icon in the Status Line) or oddbehavior can occur if the aligned curve or surface is modified later. See“Attaching curves and surfaces with history off” on page 148 for examples.

If the Attach option is toggled on in the options window, the alignedelements are joined together and you get one result.



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If necessary, you can also select the curve point and drag it to the desiredlocation.

To return to object selection mode, click the Select by object type icon on theStatus Line.

To align two curves from the marking menu:

1 Select the first curve, and while the pointer is over the curve select CurvePoint from the marking menu.



2 Click on the curve where you want to place the first curve point.

3 Shift-select the other curve and release the mouse button.

4 While the pointer is over this curve, use the right mouse button to selectCurve Point from the marking menu again.

5 Shift-click at the next align location. Another point is displayed.

6 Select Curves → Align Curves to align the curves.



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Aligning surfacesTo specify the align location for surfaces, you have to select surfaceisoparms. Use the Select by component type icon or the marking menu.

The following alignment is performed using the default option settings.

To align surface isoparms in component mode:


2 With the right mouse button, click the Lines icon to toggle Isoparms on fromthe pop-up menu.

3 Click on the isoparms where you want to align the surfaces, then selectEdit Surfaces → Align Surfaces.

Tips

A curve can only be aligned to another free curve. A curve-on-surface canonly be aligned to another curve-on-surface, provided it is on the samesurface.



To align surface isoparms from the marking menu:

1 With the pointer positioned over the first surface, use the right mouse buttonto select Isoparm from the marking menu, and click to select an isoparm.

2 With the pointer positioned over the second surface, use the right mousebutton to select Isoparm from the marking menu again.

3 Shift-select the second isoparm.

4 Select Edit Surfaces → Align Surfaces to align the surfaces.

Align limitations

• You cannot align closed/periodic curves or surface boundaries that areclosed/periodic.

• An exact tangent or curvature continuous surface cannot be guaranteed ifsurfaces are rational (if the weight is not 1.0, the surface is rational).

• You cannot align a free curve to a curve-on-surface.

• You cannot align a curve or surface to itself.

Tips

You can also hold the mouse and drag the isoparm to another location ifnecessary.

When aligning a surface to a surface, only surface isoparm boundaries canbe modified, although you can align one surface (the one that is modified)to any isoparm on the other surface.



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Aligning to a trimmed edge

You cannot align to a trimmed edge; you can only align to surface isoparms.For example, if your surfaces look like the following you can still align thetwo surfaces, but Align uses the boundary of the underlying surface of thetrimmed surface.

1 Select an isoparm at the edge of the untrimmed surface and one near thetrimmed edge of the other surface.

2 Adjust the Join Parameter value in the Channel Box if necessary.



Setting Align optionsSelect Curves → Align Curves - ❐ or Edit Surfaces → Align Surfaces - ❐ toopen the options window.

See “Editing the alignment using manipulators and the Channel Box” onpage 178 to find out how you can adjust some of these parameters in theChannel Box to suit your needs.

Setting attachment optionsAttach Select Attach if you want to attach the alignment. You can then set the

following options:

Keeping or removing multiple knots

Multiple Knots When objects are joined, Multiple Knots are created at the join parameter.Select Keep to retain these knots.

Select Remove to remove as many knots as possible without changing theshape of the object when the attach is performed.



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Determining the continuity between intersections

Continuity means that two curves intersect, or that two surfaces share aboundary. Continuity options let you specify how to achieve continuity forthe two elements. See “What is continuity?” on page 165 for moreinformation about continuity.

Position Positional continuity means that the ends of two curves or the edges of twosurfaces meet exactly. The following shows how curves are aligned witheach Modify Position option (First, Second, and Both).

When Keep Original is toggled on, notice how the curves are aligned bycomparing the position of the original curves to the aligned curve. Thealignment occurs depending on which curve is selected first (white) and last(green).

See “Changing the order of the alignment” on page 174 for more informationabout the order in which you want the curve or surface modified.

Tangent Tangent continuity exists when two elements are placed end to end, but thetangents at the two endpoints also match.

Both First (default)

Second



Curvature Curvature continuity exists when two elements that meet with tangentcontinuity also have the same curvature at the joint. When this option isselected, the curvature scale sliders are enabled.

See also “Scaling the tangent and curvature alignment” on page 177 forinformation on increasing or decreasing the tangent magnitude or curvatureat the end of a curve.

Changing the order of the alignmentYou can choose in what order you want the curve or surface modified. Thefollowing tables show what is modified when you select the ModifyPosition, Modify Boundary, and Modify Tangent options, First, Second, orBoth, for curves or surfaces.

Changing the Modify Position options

Modify Position Curves Surfaces

First

Only the shape of thefirst element youselect is modified.

The entire first curvemoves so its endpoint coincides withthe start of the secondcurve.

The entire firstsurface moves so itsend boundarycoincides with thestart boundary of thesecond surface. Someadjustments are madeto the first surface endboundary CVs.

End point of curves

curve 1

curve 2



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Changing the Modify Boundary options

Second

Only the shape of thesecond element youselect is modified.

The entire secondcurve moves so itsstart point coincideswith the end of thefirst curve.

The entire secondsurface moves so itsstart boundarycoincides with theend boundary of thefirst surface. Someadjustments are madeto the second surfacestart boundary CVs.

Both

The shapes of both thefirst and secondelements you selectare modified.

The entire first andsecond curves moveso that the end pointscoincide with eachother. The CVs at theend points are movedhalfway along the lineof minimum distance.

The entire first andsecond surfaces moveso that the endboundary of the firstsurface and the startboundary of thesecond surfacecoincide. The adjacentboundary CVs movehalfway along the lineof minimum distance.

Modify Boundary Curves Surfaces

First


The CV at theendpoint of the firstcurve moves tocoincide with the CVat the start point of thesecond curve.

All the end boundaryCVs of the first surfacemove to coincide withthe adjacent startboundary CVs of thesecond surface.

Modify Position Curves Surfaces



Changing the Modify Tangent options

Second


The CV at the startpoint of the secondcurve moves tocoincide with the CVat the end point of thefirst curve.

All the start boundaryCVs of the secondsurface move tocoincide with theadjacent endboundary CVs of thefirst surface.

Both

The shapes of both thefirst and secondelements you selectare modified.

The CVs at the endpoint of the first curveand the start point ofthe second curvemove to coincide witheach other. The CVsat the end points aremoved halfway alongthe line of minimumdistance.

All the end boundaryCVs of the first surfaceand the start boundaryCVs of the secondsurface move tocoincide with eachother. The adjacentCVs move halfwayalong the line ofminimum distance.

Modify Tangent Curves Surfaces

First


The tangent at theend of the first curveadjusts to coincidewith the tangent at thestart of the secondcurve.

The tangents at theend boundary of thefirst surface adjust tocoincide with thetangents at the startboundary of thesecond surface.

Second


The tangent at thestart of the secondcurve adjusts tocoincide with thetangent at the end ofthe first curve.

The tangents at thestart boundary of thesecond surface areadjust to coincide withthe tangents at the endboundary of the firstsurface.

Modify Boundary Curves Surfaces



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Scaling the tangent and curvature alignmentThe values in the Tangent Scale and Curvature Scale boxes increase ordecrease the tangent magnitude or curvature at the end of the curve orsurface. You can enter a value in the box or drag the slider bar. Thefollowing table shows what happens when the tangent and curvature isscaled.

Note

Curvature continuity is applied to the curve or surface that is modified fortangent continuity (see the table above).

Tangent Scale Curves Surfaces

First

Only the shape of thefirst element youselect is scaled.

The tangentmagnitude at the endof the first curveadjusts.

The tangentmagnitude at the endboundary of the firstsurface adjusts.

Second

Only the shape of thesecond element youselect is scaled.

The tangentmagnitude at the startof the second curveadjusts.

The tangentmagnitude at the startboundary of thesecond surface adjusts.

Curvature Scale Curves Surfaces

First

Only the shape of thefirst element youselect is scaled.

The curvature at theend of the first curveadjusts.

The curvature at theend boundary of thefirst surface adjusts.

Second

Only the shape of thesecond element youselect is scaled.

The curvature at thestart of the secondcurve adjusts.

The curvature at thestart boundary of thesecond surface adjusts.




If Keep Original is toggled off, the original curves or surfaces are replacedwith the aligned curves or surfaces. If toggled on, two new curves orsurfaces are created and the originals are retained.

Editing the alignment using manipulators and the Channel Box

To display manipulators on your curves or surfaces so you can edit thealignment interactively, turn construction history on before performing analignment, then select the Show Manipulator Tool.

If Continuity is set to Curvature and the scale value is more than 0, moremanipulators are added.

The example on the left shows the manipulators for the default, CurvatureScale First and Second set to 0.0. The example on the right shows themanipulators if the scale values are changed to 2.0

You can edit the options in the Channel Box for selected items. For example,if you edit the tangent scale parameters in the Channel Box for a curve,notice how the manipulators are adjusted.

Use to adjustJoin parameter

Tangent scalemanipulators

Curvature scale = 0 (default) Curvature Scale = 2



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Some of these parameters are also included in the Attribute Editor. See“Editing the alignment in the Attribute Editor” on page 180 for details.



Enter parameter values, or choose items from the Continuity Type pop-upmenus using the left mouse button. Type on or off to toggle the Reverse andSwap parameters as well as Tangent and Curvature Continuity. TheDirection U parameter determines in which direction the alignment occurs.If off, the alignment occurs in the V direction.

See the section describing the Reverse, Swap, and Twist toggles in “Editingaligned surfaces in the Attribute Editor” on page 183.

Editing the alignment in the Attribute EditorThe Attribute Editor for Align Curves and Align Surfaces reflect the optionsyou see in the Channel Box and the options window for an aligned curve oran aligned surface. If you aligned curves, the sections of the editor for theInput Curves are accessible. If you aligned surfaces, the sections of the editorfor the Input Surfaces are accessible.








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Editing aligned curves in the Attribute Editor

The Align History section of the editor for a curve alignment includesoptions you set in the options window or the Channel Box.

Input Curve The Input Curve information is read-only. It gives you access to the historyof the curves you aligned. Click the arrow buttons to select an input curveand open its section of the editor.



Positional/TangentContinuity

For details on Positional and Tangent Continuity types, see “Determiningthe continuity between intersections” on page 173.

Join Parameter The Join Parameter slider becomes available depending on the PositionalContinuity Type you select. Use Join Parameter to define the parameter onthe first/second item at which the alignment is performed. For example, ifMove First is selected for curves, the join parameter defines the point on thesecond curve where the first one is aligned.

Reverse For curves, the Reverse toggles specify whether the curves must be reversedbefore performing the alignment. Remember, Align uses the end point of thefirst curve and the start point of the second curve.

InteriorBlending

The Interior Blending sections are the same as the Tangent Scale options inthe options window. The sliders become available depending on which typeof continuity you select.



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Editing aligned surfaces in the Attribute Editor

The Align History section of the editor for a surface alignment includesoptions you set in the options window or the Channel Box.

Input Surface The Input Surface information is read-only. It gives you access to the historyof the surfaces you aligned. Click the arrow buttons to select an inputsurface and open its section of the editor.



Positional/TangentContinuity

For details on Positional and Tangent Continuity types, see “Determiningthe continuity between intersections” on page 173.

Join Parameter The Join Parameter slider becomes available depending on the PositionalContinuity Type you select. Use Join Parameter to define the parameter onthe first/second item at which the alignment is performed.

Reverse/Swap The Reverse and Swap toggles for surfaces define whether the surfaces haveto be reversed and or swapped before performing the alignment (remember,align uses the end of the first surface and the start of the second). Thereverse is done in the direction defined by Direction U (on or off) in theChannel Box.

Twist If Twist is toggled on, the second surface is also reversed in the oppositedirection of Direction U. Turn this on if your aligned surface is twisted.

For example, if you align the surfaces and the surface boundaries are goingin different directions, the following results.

When you marquee-select the surfaces, the align result is twisted. TurnTwist on either from the Attribute Editor or in the Channel Box to correctthe problem.

Surface boundaries are not going in the same direction.



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The other alternative is to check the surface U/V direction before you alignthe surfaces. Use Edit Surfaces → Reverse Surfaces to reverse the surfacedirections if necessary. See “Reversing the curve or surface direction” onpage 195 for details.

InteriorBlending

The Interior Blending sections are the same as the Tangent Scale options inthe options window. The sliders become available depending on which typeof continuity you select.

Twist off Twist on

Reverse the surface boundary on one of the surfaces.

Align result


Editing CurvesProjecting curve tangents

Projecting curve tangentsUse Curves → Project Tangent to modify a curve’s tangent at an endpointso that it coincides with the tangent of a surface or two other intersectingcurves.

You can also use this method to adjust a curve’s curvature to match a surfacecurvature, or the curvature where two other curves intersect. For instance, ifa curve’s end point is on a surface, use this function to make the curvetangent continuous with either the U or V direction of the surface where thecurve touches the surface.

Although you can use Align Curves (Curves → Align Curves) to establishtangent plane continuity between construction curves prior to constructing asurface, it can only align curves to curves or surfaces to surfaces. ProjectTangent can be used to easily re-establish tangent continuity of a curve withtwo other curves or with a surface before constructing the next surface.

To project a curve tangent onto a surface:

1 Select the surface you want to use for the project tangent, then select thecurve that you want to modify.

2 Select Curves → Project Tangent.



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To project a curve tangent onto curves:

1 When projecting curve tangents, make sure the endpoint of the curve youwant to project is located at the intersection of the other curves.

2 Select the curve for which you want to project a tangent first then Shift-selectthe other curves.

3 The tangent is projected depending on which curve you select last(highlighted in green).

Note

In some cases, you cannot project one curve tangent onto two surfaces atdifferent ends of the curve. You must be careful that there are enoughinterior CVs to avoid any overlap. For instance, if the curve is cubic andyou want to project both ends of the curve with curvature continuity, youshould make sure that the curve has at least three spans (that is, a total ofsix CVs).

Intersection point



Setting Project Tangent optionsSelect Curves → Project Tangent - ❐ to open the options window.

Defining the construction type

Construction The following Construction options lets you determine what constructionmethod is used to project the curve.

The default project tangent Construction type is Tangent. The curve ismodified by projecting its tangent vector where it intersects the surface ontothe tangent plane of the surface. This means that only necessarymodifications are made to the start or end of the curve where it intersects thesurface.

If you select Curvature, the curve is made tangent and curvature continuouswith the surface in the direction of the tangent vector. An extra manipulatoris displayed on the curve to let you adjust the Curvature Scale value. (TheCurvature Scale slider is also displayed in the options window when thisoption is selected).



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Setting the tangent align direction

Tangent AlignDirection

The Tangent Align Direction options provide a convenient way to either:

• reverse the direction of the curve’s tangent vector,

• automatically align the tangent vector with either the U or V parameterdirections of the intersecting surface or two curves.

Select either U or V to pick which tangent you want to use for theadjustment. U is the U direction of the surface, or the second selected curve.V is the V direction of the surface, or the third selected curve.

Normal is the normal vector of the tangent plane. Select the Normal optionto make a curve normal to or perpendicular to a surface or two curves.When selected, the curve is no longer tangent continuous to the surface sinceit is perpendicular to the surface.

Notes

When you select Normal, it becomes the mode you are working in for thecurrent curve modification. To return to the general project tangentoperation, select either the U or V tangent align direction.

Tangent rotation is not available when the Tangent Align Direction isNormal.



Scaling the tangent

Tangent Scale The Tangent Scale slider displays the current tangent scale factor. Scalingthe tangent adjusts the length of the tangent vector without changing itsdirection. You can adjust the tangent scale by clicking and moving the slider,or by entering a value. A negative scale factor reverses the direction of thetangent vector.

Rotating the tangent

TangentRotation

The Tangent Rotation slider displays the current tangent rotation angle.Adjusting the rotation rotates the tangent vector on the tangent planedefined by the surface intersection. You can adjust the tangent rotation angleby clicking and moving the slider, or by entering a value.

Adjusting the curvature scale

Curvature Scale Project tangent works by first selecting a curve to modify and then selectinga surface or two other curves that intersect with either of its end points. Thecurve is modified by projecting its tangent vector where it intersects thesurface onto the tangent plane of the surface.

If Curvature is selected as the construction type, the curve is made tangentand curvature continuous with the surface or curves in the direction inwhich the tangent vector is going.

Adjusting the Curvature Scale value modifies the curve in such a way thatthe tangent or curvature doesn’t change at the curve or surface intersectionpoint. For example, if you modify a curve at its end point, the curvatureslider moves the third CV from the end of the curve along a line that joinsthe end two CVs of the curve (for instance, along the tangent vector line).Such a modification doesn’t change the curvature at the end of the curve, itjust adjusts the tangent vector.

Reversing the tangent vector direction

ReverseDirection

Toggle Reverse Direction on or off to change the direction of the tangentvector so that it points in the opposite direction. Reverse Direction simplymultiplies the current tangent scale factor by -1.0.

Note

If you change the Tangent Rotation value, the curve is no longer tangentto the surface or two other curves.



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Toggle Keep Original on to keep the original curve after the projection isperformed.

Adjusting the tangent interactivelyWhen you select the Show Manipulator Tool after you project a tangent ontoa surface, manipulators display as well as editable parameter boxes in theChannel Box.

You can click-drag these manipulators to interactively adjust the curvaturescale, tangent scale, or tangent rotation of the curve. You can also entervalues in the Channel Box, or in the Numerical Input line when amanipulator is active.

Curvature manipulatorsThe manipulators correspond to the Construction method you used in theoptions window. For example, if the project tangent Construction method isCurvature, an extra manipulator appears.

If the Curvature Scale value does not equal 0, the Curvature Scale Pointmanipulator appears at the specified scale location. In the following, thescale value is 4.0.

Curvature Scale Pointmanipulator



Tangent manipulatorsThe following examples show the manipulators for a Tangent Constructionmethod.

Click-drag the Rotation manipulator to rotate the tangent vector.

Click-drag the Tangent Scale Point manipulator to adjust the tangent scale.

The same manipulators appear for curves.

Rotation manipulator

Tangent Scale Point manipulator

Curvature Scale Point manipulator

Rotation manipulator



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Editing the projected tangent in the Attribute EditorTo edit a projected tangent, use the Attribute Editor. To open the AttributeEditor, either:





Tangent Scale Point manipulator



The Attribute Editor for a projected tangent contains the same attributes youset in the options window and the Channel Box. See the option descriptionsfor details.


Editing CurvesReversing the curve or surface direction

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Reversing the curve or surface directionUse Curves → Reverse Curves to reverse the sequence (direction) of CVs ona curve. Use Edit Surfaces → Reverse Surfaces to reverse and examine thesurface normals for surfaces and trimmed surfaces.

To reverse the direction of CVs on a curve:

1 Make sure the curve is active.

2 To display the curve CVs, select Display → NURBS Components → CVs.

3 Select Curves → Reverse Curve. The CVs are reversed along the Uparametric direction by default.

To reverse the surface normal direction:

See “What you need to know about surfaces” on page 243 for moreinformation about the surface direction and surface normals.

1 Make sure the surface is active.

2 To display the surface CVs, select Display → NURBS Components → CVs.

3 Select Edit Surfaces → Reverse Surface. The surface normals are reversedalong the U parametric direction by default.

See “Changing the direction of surface CVs” on page 197 for moreinformation on how to reverse the surface CV direction.

Tip

Since motion path curves follow the direction of the curve, you can useReverse to change the path direction.

After ReverseStart CV



Setting Reverse Curves optionsSelect Curves → Reverse Curve - ❐ to open the options window.


Toggle Keep Original on to determine whether the original curves areretained after a Reverse operation is performed.

To switch start and end CVs using the Show Manipulator Tool:

1 Check to make sure Construction History is on in the Status Line ormanipulators do not display during the Reverse operation.

2 Select the Show Manipulator Tool, toggle Keep Original on, and thenreverse the curve CVs to display a reverse curve manipulator. Click thismanipulator to interactively reverse the curve’s start and end CVs.



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Setting Reverse Surfaces optionsSelect Edit Surfaces → Reverse Surfaces - ❐ to open the options window.

Changing the direction of surface CVs

The following is a close-up view of the U and V indicators on a surface.

When you reverse the Surface Direction, notice how the indicators changedepending on what you choose.

SurfaceDirection

Select U to reverse the CVs along the U parametric direction. U is the defaultsurface direction.

Select V to reverse the CVs along the V parametric direction.

Select Swap to exchange U and V parameterization. Selecting an item asecond time using the same direction restores the original CV sequence.Reversing the sequence of CVs for a surface reverses the surface normals.

Select Both to reverse the CVs and normals along both U and V parametricdirections.

U and V indicators.



To quickly reverse a surface:

To quickly reverse a surface in a specific direction, select an isoparm andthen select Edit Surfaces → Reverse Surfaces without opening the optionswindow.

Editing the reversed item in the Attribute EditorThe Attribute Editor for a reversed curve or surface contains the same curveand surface history attributes for a curve or an object. See “Editing curves inthe Attribute Editor” on page 79 and “Editing objects in the AttributeEditor” on page 227 for details.

Reversed direction

Reversed direction

Reversed direction


Editing CurvesRebuilding curves

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Rebuilding curvesUse Curves → Rebuild Curve to rebuild a NURBS curve or curve-on-surfaceto reduce data and construct smoother curves.

To rebuild a curve:

1 Click on the curve or marquee-select the curves that you want to rebuild.

2 Select Curves → Rebuild Curve.

The curve is rebuilt based on the current option settings. In the followingexample, the curve is rebuilt with the default settings.

3 Toggle Keep Original on in the options window (it is off by default) andselect Display → NURBS Components. Now you can see the CVs or editpoints on the curve when you rebuild the curve. This lets you easily verifyhow the rebuild affects the curve.

4 A new curve is rebuilt on top of the original and becomes the active curve.You can move the new curve and select the original curve to try differentoption settings. This way you can compare the results and delete the curvesyou don’t want.

Original curve with CVs Rebuilt curve



5 You can also select the original curve from the Channel Box by clicking theheading to display and edit its parameters if necessary.

Setting Rebuild Curve optionsSelect Curves → Rebuild Curve - ❐ to open the options window.

The Rebuild Curve options window changes to include the optionsassociated with a selected option setting, or to hide the options you don’tneed.



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Changing the curve rebuild typeThere are various options you can set to rebuild your curves to suit yourneeds. The options window changes depending on the type of rebuild youselect.

Rebuilding the curve uniformly

Uniform Select Uniform (the default) to rebuild a curve with uniformparameterization. You can change the number of spans and degree of thecurve you want to rebuild. The Number of Spans and Degree valuesbecome available. You can enter a value in the boxes or use the slider bar.When you press the Rebuild button after you change the values, the curve isrebuilt as a uniform knot curve of the specified degree and number of spans.

Reducing the number of spans on the curve

Reduce If Reduce is selected, a knot is removed only if its removal does not causeany of the remaining CVs to move by a distance greater than the tolerancesetting. A higher tolerance setting results in a greater span reduction. See“Setting the curve’s tolerance,” next.

Setting the curve’s tolerance

Use Tolerance If the Rebuild Type is Reduce or Curvature, the Use Tolerance options aredisplayed in the options window.

These options let you rebuild the curve within a specified tolerance of theoriginal curve. You can select to apply global tolerance or set the specifictolerance for this function.



If you select Global tolerance, the Positional value you set in Options →General Preferences → Modeling is used.

Select Local tolerance to display the following box. You can enter a newvalue to override the Positional tolerance value you set in ModelingPreferences.

Local tolerance is useful when you often want to change these values often,but don’t want to change the Global tolerance.

Matching the rebuilt curve’s geometry to another curve

Match Knots More than one curve is required if you want to use Match Knots.

Select Match Knots to rebuild a curve to match the knot values, degree, andnumber of spans of another curve. The rebuilt curve is matched to thesettings of last curve you select (the green curve).

The Keep toggles are available when you select this Rebuild Type and theMatch Curve input curve information is available in the Attribute Editor.See “Editing the rebuilt curve in the Attribute Editor” on page 206 fordetails.

Removing multiple knots

No MultipleKnots

Select No Multiple Knots to remove all of the multiple knots. The resultingcurve is the same degree as the original curve. The Keep toggles are notavailable when you select this option.



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Rebuilding the curve with more edit points

Curvature Select Curvature to insert more edit points in the areas of higher curvature.The resulting curve is the same degree as the original curve.

The Keep toggles are not available when you select this option, however theUse Tolerance options are displayed. See “Setting the curve’s tolerance” onpage 201 for details.

Setting the parameter range

ParameterRange

The three Parameter Range options are used to specify how parameters areaffected during the rebuild.

If 0 to 1 is selected (the default setting), the resulting curve’s parameterranges from 0 to 1.0.

Keep means the rebuilt curve’s parameter range matches that of the originalcurve.

Tip

While rebuilding curves to remove any multiple interior knots, quite oftenthe shape of the curve is lost. If you want to preserve the shape of thecurve, enter the following command in the Command Line:

setAttr rebuildNodeName.fr false



If 0 to # spans is selected, the resulting curve’s 0 to # spans gives you integerknot values which makes it easier for numerical input. If using the UniformRebuild Type, this option always gives you integer knot values. Forexample, if you want to use Detach Surfaces on an isoparm and you preferto type a value, it is easier to enter the number 2 than something like 0.362.

Selecting elements of the original curve to keep

Keep toggles The Keep toggles, Ends, Tangents, and CVs, are used to specify whether ornot you want to keep the end points, tangents, or CVs of the original curve.The Ends toggle is on by default.

Changing the number of spans on the curve

The number of spans in the resulting curve is set by the value you enter inthe Number of Spans box.


The Degree of the resulting curve is determined by the U or V degree youselect. See the description “What is the curve degree?” on page 55 forinformation on curve degrees.

Number of Spans = 2

Number of Spans = 10

Number of Spans = 4(default)



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If Keep Original is toggled on, a new curve is rebuilt on top of the originaland becomes the active curve. You can move it and select the original curveto try different option settings. This lets you compare the results and deletethe curve you don’t want.

Editing the rebuilt curve from the Channel Box

When you rebuild a curve, its parameters are displayed in the Channel Boxwhen you click the rebuildCurve heading. These options are also availablein the options window and the Attribute Editor. You can enter values in thevalue boxes, type on or off in the toggle boxes, or select items (Rebuild Typeor Degree) from a pop-up menu.

Note

If the rebuild is not successful, the temporary curve is not created and theoriginal curve remains active.

Cubic, degree 3 (default)

Linear, degree 1



Editing the rebuilt curve in the Attribute EditorTo edit the rebuilt curve’s attributes, use the Attribute Editor. To open theAttribute Editor, either:





The options you set in the options window or the Channel Box aredisplayed. See the option descriptions for details.

Input Curve The Input Curve information is read-only. It gives you access to the historyof the original curves you rebuilt. Click the arrow button to select the curveand open its section of the editor.

Match Curve The Match Curve read-only information is made available only if there ismore than one curve and Match Knots is selected in the options window.

nurbs modeling 1

Documents

surfaces options setting

isoparm options setting

setting nurbs

setting attach curves

options lofting curves

duplicate curves options

fillet curve options

close curve options