question about obj files containing multiple objects

[jg10545]

Hey, I've got a possibly-naive question I'd love some insight on from any of the experts here. This may be related to #1572 but I'm not 100% sure.

Following the "Render a textured mesh" tutorial I can reproduce the cow picture pretty easily:

If I load the cow .obj file into Blender, add another object, and export it to a new .obj file:

When I run that same tutorial code with the new mesh file, PyTorch3D wraps the cylinder with the cow texture:

This doesn't appear to be an error in the wavefront files; the .mtl shows a material but not a texture for the cylinder (and if I import it back into Blender it's still green).

Is this expected behavior? Am I missing something obvious? Any workarounds?

Thanks in advance for any insight!

[bottler]

We only support a single texture uv-map per mesh. Loading an obj file produces one mesh in PyTorch3D. I don't know exactly what has happened here: e.g. does the OBJ file know that it contains two mesh pieces, only one of which is textured, and PyTorch3D ignores that, or does blender save something somehow with a single texture all over.

If you want the cylinder to be green in PyTorch3D, perhaps this would work:

• export just the cylinder to OBJ.
• Load the cylinder and cow obj files into pytorch3d, producing two Meshes.
• Assign a new TexturesUV object with a constant green color to the cylinder mesh.
• Use join_meshes_as_scene to amalgamate the two meshes, which will automatically amalgamate their textures into a single larger texture map.

[jg10545]

@bottler thank you, the join_meshes_as_scene() function worked great!!