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python/convert_maya_to_usdskel
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README.md
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README.md

This Python package exports an animated skeleton (with a skinned mesh) to disk. It's a basic implementation of a UsdSkel exporter. That said, it's mainly for learning purposes and to see how Maya and USD fit together during exporting. This tool will be helpful to 2 types of people:

  • Someone looking to understand how UsdSkel works with a practical example
  • Someone who cannot use USD's pre-existing Maya exporter plugin and have to actually write the UsdSkel export process from scratch

If you fall under either camp then you will get a lot out of trying this tool out. But if you aren't learning UsdSkel or aren't expected to re-write an exporter, feel free to skip this project.

Maya Scene Requirements

  • The DAG graph needs to looks like this
    • root (Group node)
      • joints (Joint node)
        • joints1
        • joints2
        • joints3
        • jointsEtc
      • geometry (Group node)
        • mesh1
        • mesh2
        • mesh3
        • meshEtc
    • The top-most group that has both the joints and meshes is used as the UsdSkelRoot

There's an example scene file located at example/joints.ma which already has this set up.

To run

  1. Load Maya. (Important: This assumes that Maya's USD plugin is installed correctly)
PYTHONPATH=$PWD/python:$USD_INSTALL_ROOT/python:$PYTHONPATH maya

  1. Open example/joints.ma to get a scene with joints + a bound mesh or create your own

  2. Run this Python code:

from convert_maya_to_usdskel import converter

node = 'root_joint'
converter.write_rig_as_usdskel(
    node, 
    "/SkeletonRoot",
    "/SkeletonAnimation",
    "/tmp/test_export",
)

Disclaimers

This script exports a skeleton definition and animation in a single export command.

In a real pipeline, the command would be split into 2 parts:

  • A rigger would export the skeleton
  • An animator would export just the animation

This script exports in a single step to keep the code simple. But most likely, when exporting an animation, you would link to a USD file for the skeleton that already has been written to disk.

  • Generally speaking, only a basic skeleton could be exported like this.
    • Joints with offset groups aren't respected (as well as other more complex rigging features)

References

https://toolchefs.atlassian.net/wiki/spaces/ASD/blog/2018/09/03/198737921/Atoms+Cache+To+USD

https://www.youtube.com/watch?v=ECS-ntgnf24

https://atoms.toolchefs.com/

https://github.com/meshula/usdskelutil