Unify normals from CAD files

[Anonymous]

Hello, I'm a 3D Designer working in the consumer products industry. Often we receive CAD models from the industrial design team and when we import the models into maya there are a lot of normals facing the wrong direction. I've tried all of the mesh display options, and even had a friend in the movie industry write a script to try to get all of the faces to face the right direction, but haven't been able to get it to work. This leaves us no choice but to go in and flip all of the back facing normals manually before we render, which takes a lot of time. Maya obviously can see the direction normals are facing on a model, I feel like there should be a way to have maya flip them to all face the same direction. Is this possible? I'm stumped. I've attached an image to demonstrate what I'm saying, the one on the right is the before model with all of the mismatched normals, and the one on the left is the corrected model after manually fixing it, which is the desired result. Thanks!

[_sebastian_f]

my guess would be that the model consists of separate shells of faces which are not properly connected. you can check this by entering face mode and double click on a face. does it select the whole model or just parts of it? sometimes it also happens that only some verts are connected but not the neighboring edges i.e. which would count as a single shell but normals can not be determined by maya. unfortunately a pretty common problem when dealing with cad files depending how well they are built and cleaned before export. in my opinion the issue is more on the cad modelers side. which software is used? in alias i.e. it would be very easy to check and unify the normals with a couple of clicks.
if there is no option to do it i would select the whole model and perform a merge vertices with a very low threshold, make sure the normals are not locked and try again.

[Anonymous]

Hello Sebastion,

Thanks for the reply. I've unfortunately tried all of those methods, you're right in that the faces are usually not connected when the CAD model comes in, I always have to merge the verts before I try to work with it. The problem is that even after the faces are all connected the normals are still flipped, and I can't find a combination of conform/set to face/average normals that will make all of the faces face the right direction. You're also right in that the problem is definitely with the way it's built or with the way it's exported but a lot of the CAD's we get are from other companies where we don't always have a way to communicate with them to try and explain the issue. There are some industrial designers we have in house however, and they're using SolidWorks. We asked them if there was a way on their end to unify the normals and they couldn't seem to figure it out. Do you think it'd be possible for one to write a script that would be able to handle something like this? Thanks again.