### Rigging in the muscle system

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First of all, I'm just starting out learning Houdini.

This is a question about rigging in the muscle system.
I read the sub-documents of Muscles and tissue.

Suppose I have 3 parts;

1) Character body (geometry)
2) All individual muscles and bones (geometry) made to fit this body
3) Rigging done in Houdini

Question

1. In the muscle system, where should the rigging be on the body or on the bones?
If it's a body, bones and muscles automatically follow the body, or if it's a bone, muscles and bodies automatically follow the bones?

2. Is it possible to import geometry (body/bones) from a rigged object without rigging errors?
If so, where should this import be? Is it the 'Object Merge' at the start of the muscle pass?

3. Do the weights of the rigging offset the constraints and forces of muscle, tissue and skin? (If it must be body rigging in 1)
Edited by acdum1857 - July 26, 2023 23:32:03
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acdum1857
1. In the muscle system, where should the rigging be on the body or on the bones?

In a full simulation of muscle and tissue these are the broad steps:
-rigging and animation is applied to the skeletal bones surfaces only.
-muscles are made solid from your muscle surfaces in a static rest position.
-The solid muscles are then constrained to the animated bones (bone surfaces) and cached to disk as a sequence of geometry files.
-the Muscle Solver is run to perform the simulation
-Tissue is built as a solid from your creature surface.
-the solid tissue is constrained to your muscle and bone geometry in a static rest position.
-The Tissue Solver is run to simulate the tissue which is constrained to the cached muscle and bone animation.

So the short answer is, you animate the bones. The bones drive everything else.

acdum1857
2. Is it possible to import geometry (body/bones) from a rigged object without rigging errors?
If so, where should this import be? Is it the 'Object Merge' at the start of the muscle pass?

Short answer is, yes. It's possible.
The Object Merge named: Import_Animated_Bone_Surfaces should point to the sop that displays the animated bones.

And question 3 is probably answered in #1 above.

The video tutorial is also not applicable to the SOP based workflow we've had since Houdini 19. That video demonstrates the outdated Object-Level workflow.
john mariella
Senior Technical Director
SideFX
www.sidefx.com