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Houdini and editing an FBX skeleton rig

jim c

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I've imported an FBX file and it has an animated skeleton and some geometry. For the most part everything looks pretty good but there's a couple of places where I'd like to adjust the bones position. And this is where I'm sort of confused.

As I understand it, in a "normal" Houdini rig, you have a root bone, and then a series of bones underneath. To adjust the rest or pre-deformation position of the bone you need to adjust the pre-transform.

However with the FBX "rig", it's just a series of hierarchical Null object, with a single bone parented to each null, with the bones length generated by an expression that determines the length between the two nulls. So I'm not entirely sure how I do this. The nulls are keyframed, not the bones, each bone is independent of any other (i.e. no bone is actually directly parented to another in the FBX rig). Is it even possible to edit the rig this way, or do I need to use some other app like Maya or Max to edit the rig, and then bring that in Houdini?

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I guess you could try repositioning the nulls, but I'm not sure what effect that will have on your animation. FWIW, something to try:

- Find some frame that is convenient to edit

- On the null you want to reposition, turn on it's Keep Position When Parenting (KPWP) parameter

- Insert a new null as the parent of the one you just turned on its KPWP

- Offset the new null to a desired location.

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Edward, I did try moving the nulls around, and that screwed all sorts of stuff up. I'm doing this for the Mixamo competition, and realized that I'd have to adjust the animation for that anyhow, and to do that, I need to upload the FBX back to the mixamo webservice. So I'd need to be able to export it from H, and my version doesn't allow for that, so I'm SOL no matter what. I was able to open this in Modo, edit things there, export the fbx and regen the animation, so at least I have a work around.

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