Hi Sebastian - that's unfortunate re: Cheetah3d not using the vertex normals from the file and instead calculating new ones, it's discarding some important data there. With CAD data, it's never going to be able to calculate the same normals since all it has to work with are a bunch of facets and not the original NURBS surfaces.

One thing that can help somewhat with that is to try and make a more finely diced up export from MoI, using the "Divide larger than" option to break polygons down to a more uniform size. But even then you're still going to see various imperfections in the shading. It's soooooooo very much better to have the true vertex normals - getting the true vertex normals over results in a super smooth and perfect looking render without any messing around at all.

Automatically calculated normals don't work very well with things like a large polygon face right adjacent to a bunch of small polygons for a rounded edge, it's too easy for the little poly on the rounded edge to overly influence the shading on the large polygon with stuff like that, and that kind of large flat face next to a rounded edge is a common kind of structure with CAD models. More organic sub-d models tend to work ok with automatically calculated normals because they're typically constructed out of all the same general sized polygons that kind of gradually bend around.

So some rendering programs that have become very focused just on dealing with sub-d models may not really know how to deal with CAD data that has a different structure than organic sub-d type models. But that's becoming fairly rare now, most renderers out there are able to import vertex normals these days.

- Michael