# Non-Manifold Geometry

#1

I’ve a pretty good idea what non-manifold geometry is, however, there is something i would like to have clarified. To help out i will provide two examples of simple meshes for you to look at.

My First example is a coat i modeled for a character of mine. Notice at the end of the sleeve, all i have done is extrude and fold the geometry in to create the appearance of volume/ thickness, the same was not done for the opening at the front of the coat. The other sleeve is missing because my character wont need it. A mechanical arm will be placed there.

Coat_sample.jpg

In my second sample i have created a Jersey. Here i have done the same for the openings, extruded and folded the geometry inward.

Jersey_sample.jpg

Would either or both of these meshes be considered non-manifold?

My reason is because i have run into problems with displacement maps from zbrush in maya. I have read that the issue is caused by non-manifold geometry.

Would it be a good idea to model an inner wall to such a mesh like the ones i have? Or would they be fine as they are?

#2

the only way i can guess to say it could be nonmanifold is if you connected the folds back into the geometry from which you extracted it… (does that makes sense?)

you could always run the cleanup tool to check though.

#3

Yes, what you said makes total sense. Had i done that i would have three faces sharing one edge, which is bad.

I guess what im really asking is, Should i close off my models by building an inner surface?

Or

Is folding the edges in like i’ve done good enough?

#4

You don’t need to have an enclosed volume (no holes). Having a ‘shell’ is fine.

#5

non manifold means you couldn’t make it in real life. So a solid cube is manifold. A cube with a face removed and no internal thickness is non-manifold since faces of zero thickness cannot exist in real life. does that help?

#6

It helps a lot folks. Maya has a funny reaction to zbrush displacement maps and i’ve suspected my models might have something to do with it as well. Some models give me issues, others don’t. All this input has given me a pretty good idea of what i’ve been doing right and wrong.

Thanks to everyone.

#7

Another example of a non-manifold mesh is when neighboring polygon normals, of the same mesh, are facing opposite directions. This will cause what appears to be erratic behavior with certain modeling tools with, for example, the append to polygon.

#8

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