Full Version: CAD to Polygone conversion.

From: Berube [#1]
 9 Nov
To: ALL

Hello Everyone,

I hope this message finds you well.

A few of us at work are currently trying to make the most of CAD created models in a VFX pipeline, where most geometry needs to be converted in Quaded Polys.

I was wondering what were the current best practices towards translating CAD models in Polys, while retaining most of the initial CAD curvature, as a new Quaded Polygonal model.

A few constraint that are needed on our ends are:

-Quads
-Merged vertices
-Connected Edge flow

Thoughts?

-J

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From: Michael Gibson [#2]
 9 Nov
To: ALL

Hi Berube, well typically CAD models don't need further subdivision smoothing on them, so your all quads and connected edge flow constraints are kind of unusual. Normally a CAD model is smoothed in a different way from that, it's got filleted surfaces where things are supposed to be round and as long as you get vertex normals coming through those areas will render smoothly without needing to be all quads.

Are you doing something unusual to the CAD models that you need to have those specific constraints?

- Michael

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From: Berube [#3]
 9 Nov
To: ALL

Hi Michael,

Thanks for the reply.

Ok, let's talk about the best, unconstrained way first then.

What is the current best way to export CAD to OBJs?
The N-Gone method is looking great but wish we could get an all Quaded version.

Thoughts?

-J .

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From: Michael Gibson [#4]
 9 Nov
To: ALL

Hi Berube, well the best way kind of depends on what you're going to be doing with them. If your downstream tool supports n-gons then it can be nice to use that since it will make a cleaner wireframe that more closely resembles the structure of the original CAD data. The main thing is to make sure when you open the .obj file in your rendering application that you're getting vertex normals coming through. When MoI writes the .obj file it also writes vertex normals to be used for smooth shading and those normals come from the original CAD data so it makes for high quality shading.

There isn't any way to get an all quads version directly out of MoI currently. You could use a retopology tool to do that but it's more likely to warp the model and mess it up than do anything useful. There just really isn't any point to having all quads on a CAD model since it won't have subdivision smoothing being applied to it.

One other tip is if there are areas of shallow curvature in the model it can be good to expand to the detailed options and put in a distance value in the "Divide larger than" field to ensure polygons larger than that length are further subdivided.

- Michael

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From: Robert (MAESTROROBERTUS) [#5]
 17 Nov
To: ALL

I have tested a quad mesh of another product and I'm not really excited of that idea at all. To be fair so, a polygon size limit could be useful. Some application have problems with polygons larger then 100 vertex, which can happen in some cases. I haven't found a tool where I can set max poly edge count, but in Modo you can select all polygons with more then 4 vertex and make them quad or tries with a single click. Can be useful.
Ideal max size of polygons so, would be between 5 and 64. So this could be really useful.

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