Convert OBJ to USD

[ft-lab]

Description

Fixes #6

Convert OBJ to USD.

• Supports multiple meshes in obj files

Updated:

If obj contains only one mesh, it will be processed using the same code as mujoco-usd-converter.

If obj contains multiple meshes, the multiple meshes will be placed in Xform.

two_meshes.obj

o Cube_Red
v 0.500000 0.300000 0.500000
...
o Cube_Green
v 0.500000 -1.300000 0.500000

->

two_meshes (Xform)
  Cube_Red (Mesh)
  Cube_Green (Mesh)

Checklist

• I am familiar with the Contributing Guidelines.

[codecov]

Codecov Report

❌ Patch coverage is 97.46835% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
urdf_usd_converter/_impl/mesh.py	97.46%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[andrewkaufman]

I don't really understand the intricacies of mutli-object OBJs with respect to the tinyobjloader API, but I have found that many of the processing functions are quite slow. You need to be very careful about when & how to access the indices, normals, and texcoords arrays. If you do it subtly wrong you incur either array copies or per-index lookups between c++ & python, both of which are quite slow.

We should find the largest robot we can that has normals & uvs and perf test on that to figure out if our use of tinyobjloader is efficient.

If this does turn out to be slow, and there really is no other approach to split arrays between shapes, then we should have 2 code paths

• fast path for single shape OBJs -- exactly what we have in MJC
• slow path for multi shape OBJs