Capture geometry to bones - Houdini online help

Overview

Capture weights

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.
You can 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.

Important tools and nodes

Tools	Bones tool, Capture geometry tool, Edit capture regions tool, Edit capture weights tool, Mirror tool, Mirror capture weights tool, Paint capture weights tool
Objects	Bone object
Other nodes	Inverse Kin CHOP

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.

Tip

This submenu also lets you edit the “rest” pose that controls IK the solution. See how to edit the rest position .

Capture geometry by proximity

To bind surfaces to bones, you specify a 3D volume around the bone, inside which the bone will “capture” surfaces. You will control the capture regions using manipulators that define the volume in which the capturing will occur.

Tip

The skeleton and skin surfaces should overlap in 3D. Switch to the capture pose if you need to use a specific pose for capturing geometry.

To...	Do this
Bind geometry to bones	Click the the Capture Geometry tool on the Character shelf. Select the surfaces you want to capture, then click to finish the selection. Select the root object of the character/bone chain you want to bind the geometry to, then click to finish the selection. In shaded mode, the geometry changes to the color of its capturing bone. Geometry that is not captured is white. If part of a surface is mistakenly captured or not captured, edit the capture region of the bones (see below). Once the surfaces are successfully captured, you can use the Pose tool to pose the skeleton and the surfaces should deform to follow the skeleton.
Edit the capture region of bones	Click the Edit Capture Regions tool on the Character shelf. Select the bones you want to capture geometry for, then press Enter to confirm the selection. Manipulators appear on the bones showing each bone’s capture region (the volume around the bone which inside which geometry will be bound to the bone). Drag the handles to change the size of the capture region. Hold ⇧ Shift and drag a capture region handle to edit all the handles on a bone at once.

To...

Do this

Bind geometry to bones

Click the the Capture Geometry tool on the Character shelf.
Select the surfaces you want to capture, then click to finish the selection.
Select the root object of the character/bone chain you want to bind the geometry to, then click to finish the selection.

In shaded mode, the geometry changes to the color of its capturing bone. Geometry that is not captured is white.
If part of a surface is mistakenly captured or not captured, edit the capture region of the bones (see below).
Once the surfaces are successfully captured, you can use the Pose tool to pose the skeleton and the surfaces should deform to follow the skeleton.

Edit the capture region of bones

Click the Edit Capture Regions tool on the Character shelf.
Select the bones you want to capture geometry for, then press Enter to confirm the selection.
Manipulators appear on the bones showing each bone’s capture region (the volume around the bone which inside which geometry will be bound to the bone). Drag the handles to change the size of the capture region. Hold ⇧ Shift and drag a capture region handle to edit all the handles on a bone at once.

Behind the scenes

If you go into the Geometry object containing the captured surfaces, you will see Houdini has added a Capture node and a Deform node to the existing chain. These nodes use the bone movements to deform the geometry.

Paint capture weights

See Paint Capture Layer shelf help.

Detail Attributes

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.

pCapt	Output by the Capture and Capture Proximity SOPs, stores the point weighting information. It consists of pairs of the capture region index in the pCaptPath attribute along with its associated weight.
pCaptAlpha	Output by the Capture Layer Paint SOP, contains the painted alpha information.
pCaptPath	Output by the Capture and Capture Proximity SOPs, a list of entries indicating the regions used in the capture process. Each entry consists of a path to the SOP relative to pCaptSkelRoot (below) followed by the corresponding primitive number in the SOP.
pCaptData	Output by the Capture and Capture Proximity SOPs, contains the rest transforms of the capture regions at the time of capturing.
pCaptFrame	Output by the Capture and Capture Proximity SOPs, contains the rest frame at which the data was captured.
pCaptSkelRoot	Output by the Capture and Capture Proximity SOPs, contains the parent path of all entries in the pCaptPath attribute.