Flipped normals on CAD data

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  10 October 2013
Flipped normals on CAD data

Hi guys, hoping someone can help me with this. I have a CAD data model that I'm trying to render out in Vray. The model came with negative scale transforms, so whenever I freeze the transforms it flips the normals. If I flip the normals back, it still shows up black in the viewport, even though the face normals show that it's facing the correct way. This causes the object to render out a silver metallic color instead of the blue shader that I have on it. I flipped them again and they render out with the typical flipped normals look. Usually, I would use "set to face" on the normals, but with CAD data it ends up faceting everything instead of looking smooth.

Has anyone else had this problem? I don't have any screenshots, unfortunately. I ended up just deleting the bad side and mirroring the good side over, but I'd like to find a way to fix this in the future in case I come across geo that can't be mirrored.

Thanks!
 
  10 October 2013
If you look in the Render Stats for the mesh, you will find Double Sided and Opposite attributes. I have used these in the past to fix such problems. Opposite becomes an option if you turn off Double Sided, which in your case, is probably off already.
 
  10 October 2013
sometimes you need to straighten your normals (set to face) after flipping them. But this will make your edges all hard, so you might want to try the fix above first.
 
  10 October 2013
Whenever you mess with Normals and the faces "turn black", simply Unlock Normals.

No need to set both sides or opposite to render, because that actually won't help with most of your shaders - if they're on the wrong normal, they'll render wrong.

You will be doing a great deal of this if you're working with CAD models. Oftentimes the CAD package, even Rhino, cannot tell what you wanted the normals to be. This isn't really a flaw so much, it's just that software cannot think. So we have to think for it!
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  10 October 2013
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