Hey!
Been a modo user for a few years (2.5 or so) and had a bunch of issues of my own between RC and Modo.
My first question is why do you atlas map it? Since you want to maximize your texture space, probably a manual unwrap would make more sense.
The main question, and the part I don’t really follow from your description is this:
- I export the new OBJ file combining both meshes.
Why would you combine two meshes? The way I understand it is you export your original mesh, you retopo it, uv it, project back the details on the retopoed mesh (therefor, this mesh is expected to contain approximately the same amount of triangles) and that is the one you import in RC to texture it. In this way, when you go back to the lowest subdivision, you can still keep your uvs and therefor the texture that RC gave you.
My guess, from what I understood, is that you are importing two meshes, so I think this is where RC has a problem in projecting back the texture.
Please let me know if I misunderstood something or if I should clarify more anything from what I said!
Cheers!
Dan