cleaning up bad geometry using maya's cleanup options - tuts+ 3d & motion graphi

Cleaning Up Bad Geometry Using Maya's Cleanup Options - Tuts+ 3D & Motion Graphics Tutorial

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Cleaning Up Bad Geometry Using Maya's Cleanup Optionsby Shray Khanna 12 Feb 2013

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Meshartifacts, broken verts, overlapping faces and other forms of "Bad Geometry" are an

unfortunate part of building 3D models, we've all experienced them at one time or another.

These errors can appear for anynumber of reasons and they're not always easy to spot.

In today's tutorial, you'll get a detailed overview of Maya's Cleanupoptions and how they can be

utilized to help get rid bad geometry that is sometimes hard to fnd and will cause issues when

exporting meshes toreal-time game engines.

Step 1So we'll start with a simple polygon Sphere to test all the bad geometry possibilities which can

be corrected using Cleanup.



Step 2Now to start with the cleanup go to Mesh>Cleanup... and it will open a new window called

"Cleanup Options", which has a variety of options which I'll explain as we move on.



Step 3



Now for our frst option, we need to create a type of bad geometry onour sphere, as the

default one doesn't have any kind of artifacts present. So for that simply select the "Split

Polygon Tool" and add a few cuts on some faces to make them n-gons (faces surrounded by

more than 4 edges.)



Step 4



Now open the Cleanup window again, this time using Hotbox. Press and hold Shift+Right-click

and select "Cleanup". As you see these bad sections of geometry are easily visible on the

sphere, but what if you had created something complex, like a "Roller Coaster" ride and some

of these bad sections are left. How are you gonna fnd them? That's why "Cleanup" is there to

help you fnd them.

Step 5But frst let's take a brief overview of the "Cleanup Effect" options. Under "Operation" if you

select "Select Matching Polygons" and apply it, this will select only the affected area based on

what you havehighlighted.

If we choose "Cleanup matching polygons" it will automatically correct the affected areas

without even showing that area. At frst it might seem like a great idea to let Maya auto-correct

all the artifacts,but Maya actually does a pretty poor job fxing your geometry. You should

(almost) always set this option to Select matching polygons. So we can see what is wrong

with our geometry and decide how we want to fx it.

Now there is a "Scope" option, in which if you select Apply toselected objects Maya will only

perform the Cleanup on the objects that are currently selected in your scene. If you set it to



Apply to all polygonal objects, Maya will perform a Cleanup on all the polygonal objects in your

scene.

It's always better to work on each asset at a time as it will avoid any kind of confusion. It's also

always good to keep the "keep construction history" option on as well, otherwise after using

cleanup, Maya will automatically delete your asset's history.

Step 6Now we'll move forward to the "Fix by Tessellation" tab, and select "Faces with more that 4

sides" (these are called "N-gons") which we've already created on the sphere. So after this,

select the sphere and hit "Apply", and you'll notice it has already selected the affected faces.

Now I haven't given a brief of the "4-sided faces" option as we only use this one when we

need our mesh to be in Triangles only. As of now most of the game engines accept quads,

so we really don't need that option because we don't consider 4 sided faces bad geometry.



Step 7



Now there are two different ways to correct this issue. One we can simply use "Cleanup

matching polygons" in the Cleanup options and hit Apply and it will connect the open vertices

automatically. But that gives us some extra triangles that we don't want and may affect the

shading on our asset.



Step 8



Or two, you could simply use the "Split Polygon tool" to connect the open edges where you

want.

Step 9Now for our next Fix "Concave faces", simply move the vertices and create few concave

faces.



Step 10Now under "Cleanup Options" select "Select Matching Polygons" and "Concave Faces" and hit

"Apply" and it will select the affected faces only.



Step 11Now we can simply correct it by moving the vertices to make the shapea convex face. or if our

model doesn't allow us to do that, we can simply break the quad into 2 triangles using the

"Split Polygon Tool".



Step 12Now to show you guys what "Faces with hole" is, we have to create one. For that create a

cylinder shape intersecting with the Sphere, and then Boolean it with the sphere using

"Intersection".



Step 13



Now Delete the remaining faces of the Boolean intersection. This lastremaining face with the

hole in it, in which all the vertices are open (not connected), is called a Face with a Hole.

These will give you terrible results when smoothed out and should always be taken care of.



Step 14



Now using the Cleanup Settings, select "Select Matching Polygons" under the Cleanup Effect

options and set the "Fix by Tessellation" option to "Faces with Holes", you'll get the affected

face highlighted.

And again if you set the Cleanup Effect to "Cleanup matching polygons" it will connect all the

open vertices automatically, but you also do the same thing using the "Split Polygon Tool" if

you want to control the smoothing group manually.



Step 15



Now for our next artifact "Non planar Faces" just select any one vertex, and move it inwards,

and this has created 4 Non-Planar faces surrounding that vertex. Non-planar faces are

polygons with at least four vertices that do not lie on the same plane. In other words the

vertices of a Non-planar face no longer create a fat surface in 3d space. As we can see in the

second image below.



Step 16



So applying Cleanup with "Non Planar faces" it will highlight only the Non Planar faces, and

automatic Cleanup will connect the diagonal vertices so that the quads have now changed

into triangles. A triangle is always a Planar surface in whichever form you place it or move the

vertices. Manually you can also move the vertices and change the face from Non-Planar to

planar, obviously only if your model allows it.



Step 17



Now we'll move on to "Lamina faces", which are actually 2 faces whichshare the same vertices

and sit on top of each other with merged vertices. These kinds of faces are very hard to fnd

as they blend in pretty well, you can only spot it if you fnd unusual smoothing on any part of

your mesh, where smoothing groups wont work, and applying subdivision also will create

some artifacts in this area. Now to have this shown as an example, duplicate an existing face

over another and merge all 4 vertices.



Step 18



So applying cleanup will highlight that one extra face over the otherone. And if auto cleanup is

applied, it will directly delete this extratop face. Auto Cleanup works best for the Lamina faces

issue.



Step 19



Now we'll have a look at the last case of bad geometry which consistsof 3 types of them. First

"Nonmanifold Geometry" is when 3 or more faces share the same edge on an object, for this

simply select any edge and make an extrusion out of it. There are now 3 faces all extruding

from one single edge.

Step 20Now to clean this up if we use "Select Matching Polygons" it will select the two vertices through

which these faces are connected. And if you do Auto Cleanup it will simply split these two

vertices and hence split all three faces altogether.



Step 21



You can simply check this auto Cleanup by selecting the extruded faceand moving it in space.

An alternative and the best way to get rid of this kind of Nonmanifold geometry is to delete it

directly, or simply separate that particular face.

Step 22The second type of Nonmanifold Geometry is where two or more faces share the same vertex,

yet they share no edge. Just like in the previouscase, if we collapse that same edge then we

have a face that is connected to numerous faces with just one vertex on the same object.

Now if we do an Auto Cleanup it will again split that vertex and all the connected faces will

separate from that vertex, but yet again the best solution in this case is to Delete off that extra

polygon face or simply separate it.



Step 23



Now the third and last type of Nonmanifold geometry, is when two or more adjacent faces

have opposite normal directions. To test that, simply select a few faces and then go to

Normals>Reverse, and you'll notice the hidden faces on the object. Generally these kinds of

faces are pretty visible on the object, but on some bigger assets they're really hard to fnd and

that's when Cleanup is there to help.



Step 24



In this particular case Auto Cleanup is also the best thing to do as it will automatically select the

minority faces which have opposite normals and apply the Reverse normals to them.

Step 25Now there are three more kinds of bad geometry according to Cleanup, but in reality they're

not harmful or not acceptable i.e. "Edges with Zero Length", well technically it's not zero but it's

close to "0" like "0.01 or 0.001". Selecting this option will highlight the edge that falls into this

criteria, and Auto cleanup will simply collapse this edge.



Step 26Same goes with the "Faces with Zero Geometry Area", it doesn't hurt having them if required.



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Step 27And The last one in Cleanup is "Geometry with Zero Map Area" that means the UV space of

any particular face is near to zero, and that won't happen if you have done proper UV

mapping. But just in case you need to fnd out if you've missed any faces on any asset, this

can be a very helpful way to fnd out.



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ConclusionI hope this will give you a very clear picture of what kinds of bad geometry there can be in an

asset and how we can rectify them, either manually or using the cleanup command of Maya.

Difficulty:

Beginner

Length:



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About Shray Khanna

Iam a Game-Artist from India, been working on Several AA and AAA titles for PC/PS3/X-box. I've always loved playing games since I was in School, so it's been a dream come true for me to now working in this industry :)

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tutsplus.comCleaning Up Bad Geometry Using Maya's Cleanup Options - Tuts+ 3D & Motion Graphics Tutorial

cleaning up bad geometry using maya's cleanup options - tuts+ 3d & motion graphi

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