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Constraining to SOP Level Transforms (i.e. parenting)

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Hi there!

I've found a lot of topics somewhat talking about this, but haven't been able to get anything working. I am trying to constrain or parent geometry to an animated FBX bone. In my scene, a character emits particles from their mouth, but that animation is at the SOP level. I could use a rivet, but that only tracks the position of the bone, and not the rotation. If I use a Parent Blend constraint at the Object level, nothing from the Sop level animation affects the child.

Am I missing something on how parenting works in Houdini? Or perhaps there is a better method to accomplish this kind of constraint relationship? 

Thanks for any help!

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I could use a rivet, but that only tracks the position of the bone, and not the rotation.

It actually tracks also rotation and scale but you must point to to a set of points on a tracked surface (as a point group or as points' indices). It will then use its positions to compute orientation frame or you can also create orthogonal frame on points and ask Rivet to use them instead (it will probably work faster that way).

I don't know if this is best option to constrain OBJ to FBX bone, but just for the record, you can use Rivet for it.

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On 3/14/2019 at 12:24 PM, symek said:

It actually tracks also rotation and scale but you must point to to a set of points on a tracked surface (as a point group or as points' indices). It will then use its positions to compute orientation frame or you can also create orthogonal frame on points and ask Rivet to use them instead (it will probably work faster that way).

I don't know if this is best option to constrain OBJ to FBX bone, but just for the record, you can use Rivet for it.

Wow! Realized there was only one control point in the Bone's geo network... changed my setup to rely on a group of actual surface points on the mesh and the rivet worked great. Thanks for the tip!

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