introduction to geometric modelling 20 september 2010
TRANSCRIPT
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INTRODUCTION TO GEOMETRIC MODELLING
20 September 2010
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Content
• Introduction• Types of 3D model• 2D vs 3D• Solid Modeling
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Introduction
• 3D modeling is creating an object or a part which has 3D characteristics and can be viewed 3D
• Simply, the object has depth or thickness• In 2D drafting or drawing, the object is normally drawn in XY direction.• In 3D modeling, the object is drawn in XY
and also Z direction
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3D Modeling
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• Object modeled in 3D can be rotated and view from any
angle• Generally, more complicated to create and produce compare to 2D
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• Types• 3 main types: wireframe, surface and solid
• 3D Wireframe Modeling– Show the ‘frame’ of the object in lines– quite similar to 2D, however the object has 3D characteristics
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3D Wireframe Modeling
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3D Surface Modeling
– has material/texture between the line of frame– normally no thickness– complex/advance curved surface may be produced
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3D Surface Modeling
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3D Solid Modeling
– model is made from solid blocks by combining and/or subtracting
– the solid blocks can be created by applying 3D operations on 2D object and/or adding and subtracting primitives
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3D Solid Modeling
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3D Vs 2D
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2D Vs 3D
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Solid Modeling
• Solid model consist of volumetric information & surface info of an object
• Surface of the model represent boundary between outside & inside of the object• Basic rule – all surfaces must touch another
surface
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Solid Modeling
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Solid Modeling
• Several different types of solid modeling– Primitive modeling– Constructive solid geometry (CSG)– Feature-based modeling
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Primitive Modeling
• Objects described using basic geometrical forms.
• Common geometric primitives.
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Primitive Modeling
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Primitive Modeling
Example:
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Constructive Solid Geometry
• More flexible and powerful than primitive.
• Allow Boolean Operations: union,
difference & intersection
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Boolean operation
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CSG: Example
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CSG: Example
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Feature-based Modeling
• 3D model is built using series of features, such as hole, slot, square block, etc.
• Each feature can be independent or linked to other feature.
• The geometry of each feature is controlled by modifiable constraints and dimensions.
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Feature-based Modeling
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FBM: 3D operations
• Basic concept– 2D cross-section or profile is produced– Depth is given to the profile• Generally 4 types– Extrude– Revolve– Sweep– Blend• *different terms might be used in different
software/books*
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3D Ops: Extrude
• A linear sweep, where the profile is given a depth in straight line, perpendicular to the profile plane
• Cross-section is constant, start – end
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3D Ops: Extrude
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3D Ops: Revolve
• The profile is rotated around a defined axis, 0 – 360 degree• Cross-section is constant
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3D Ops: Sweep
• The new command and is similar to the EXTRUDE command, but it concentrates on using paths to define the direction of the extrusion.
• This command SWEEP a 2D object along a path
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3D Ops: Sweep & Blend
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Steps in building 3D object
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Examples of FBM + boolean