is there an easy way to zero out a child's joints local transforms so its position and orientation match its parent? I know I can use VOPS or VEX and get inverse local transform and apply that, but surely there is a more straightforward thing somewhere to zero out local transforms?

Unfortunately you're running up against the current state of KineFX. All the tools are there at a low level, but a lot of the artist facing tools you'd find in most other DCCs aren't (yet) there. It is still very much a TD tool. Artist-friendly controls have to be written. I know side effects is working on adding more tools. They started with tools aimed at a mocap/retargeting workflow, but basic character animation tools are still missing.

So there's no tool (to my knowledge) to just zero things out. But there's easier ways than using inverse matrices. You can easily set a child's local transform to identity or copy the parent position and transform to the child. It would be easy to wrap something like this up in and HDA and you've have an easy tool to use. But again, it's up to you to write it (at the moment)...

made-by-geoff
Unfortunately you're running up against the current state of KineFX. All the tools are there at a low level, but a lot of the artist facing tools you'd find in most other DCCs aren't (yet) there. It is still very much a TD tool. Artist-friendly controls have to be written. I know side effects is working on adding more tools. They started with tools aimed at a mocap/retargeting workflow, but basic character animation tools are still missing.

So there's no tool (to my knowledge) to just zero things out. But there's easier ways than using inverse matrices. You can easily set a child's local transform to identity or copy the parent position and transform to the child. It would be easy to wrap something like this up in and HDA and you've have an easy tool to use. But again, it's up to you to write it (at the moment)...

Thanks a lot for this @made-by-geoff

Setting the "Mode" on the Rig Pose SOP for a particular joint to "Override" also seems to zero out the local transforms for that joint.