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In Houdini, once you associate skin geometry with bones, each point on the skin surface(s) has a point attribute which stores the degree to which the surface is influenced by different bones at that point. Where skin covers a joint, the skin can be affected by both bones according to percentages.
To initially associate the skin surface with the character, use the Capture Geometry tool. This tool uses Biharmonic capturing, which builds clean weights based on biharmonic functions on tetrahedral meshes.
You can further edit the volume around each bone that automatically captures geometry with the Edit Capture Region tool.
You can paint the influence of bones onto surfaces with the Paint capture weights tool.
You can view the capture weight attributes on the surface numerically with the details view.
Posing the character for capture
Houdini uses a character’s capture pose when it binds geometry by proximity to the bones. The capture pose does not have to be the same as the character rigging rest pose. You can pose the character specifically for capturing geometry, based on the position of the skin model.
Choose Edit ▸ Objects ▸ Bone Kinematics Override: Capture Pose.
Pose the character to match the model geometry.
To return to normal posing, choose Edit ▸ Objects ▸ Bone Kinematics Override: None.
This submenu also lets you edit the “rest” pose that controls IK the solution. See how to edit the rest position.
Paint capture weights
See Paint Capture Layer shelf help.
If you are using the Auto Rig you will not have to deal with detail attributes. However, if you are building your own character the following capture attributes are stored in detail attributes.
Output by the Capture Layer Paint SOP, contains the painted alpha information.