Broken normals on smoothed surfaces
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Greetings. I'm sorry if this issue was already brought up.
I am encountering a recurring bug with absolutely incorrect normals on every smooth curved surface I have. The problem is not manifested inside SketchUp itself, but appears in every file format you can export your works to. Here are screenshots to illustrate what I'm talking about (all screenshots are clickable for full resolution).
▼ Model in SketchUp, simple object consisting of two components, all surfaces with smoothed normals, smoothing angle is 45 degrees. Note how in SketchUp viewport, smoothing always looks proper and lovely.
▼ Example of exported model. Left one is identical to shown on the previous screenshot, right one was left without SketchUp normal smoothing. Problem is obvious.
At first I've though it's a problem of some certain file format or a bug of some certain exporter/workflow, but I've tested several models with:
- SketchUp .dae export
- SketchUp .obj export
- SketchUp .3ds export
- SketchUp .fbx export
- 3ds Max (2010/2011/2012) .skp import
Every single test reproduced the same result.
Then there was even more weird issue: erroneous smoothing produced in SketchUp can not be removed, edited, or replaced in 3ds Max no matter what. Even completely overriding everything with Edit Poly and using auto smoothing leaves you with unaffected SketchUp smoothing once you export your model to any subsequent file format - as if the modifier never existed at all.
3ds Max, after the introduction of native .skp import in version 2011, seems to be supplemented with some kind of additional support for SketchUp smoothing - you never see anything wrong with it in 3ds Max viewport. I almost looks like SketchUp smoothing rendering technique was ported to 3ds Max to display smoothing in imported models just like you see it in SU viewport. So, basically, it turned out I can't rely on 3ds Max to check whether smoothing was proper or not in a particular case (simply put, viewport is often "lying"). Each file format I've mentioned above was checked for faulty smoothing in third-party software (other DCC packages, some 3d engine, and so on).
The only exceptions seemingly unaffected with this error are spheres created from rotation of a circle (you know that SketchUp trick), and very simple cases of smoothing like a barrel (with smoothed edges situated on one axis) or a wheel. I don't know why, but the problem does not manifest itself on these objects (or is just very unnoticeable under the lighting conditions I've set up):
Basically, what I see here is completely broken smoothing on every complex curved surface. Obviously, this is an absolutely staggering issue - I can't show my client anything with such a problem.
I believe that many people on this forum work with exporting SketchUp models, so I've wanted to ask if anyone else have encountered this issue, and if there is any solution to it. This is extremely important to me. Thanks in advance for any help!
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