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Chapter 39: Animating with CAT and Creating Crowds
FIGURE 39.1
CAT includes several default preset rigs such as this alien character.

One key advantage of CAT rigs over the rigs available in Character Studio and Biped is that they aren’t lim-
ited in their structure. Although the available CAT rig presets includes a Base Human and even a Bip01 rig
that are used for animating human characters, some of the other presets are dragon, horse, lizard, spider,
and centipede. These different rigs have multiple legs, arms, and wings and all are easily controlled.

Modifying prebuilt CAT rigs
With a prebuilt rig added to the scene, you can use the Transform tools to select and move the bones to
match the skin mesh. The arms are automatically set up as a Forward Kinematics (FK) chain, so rotating the
upper arm bone automatically rotates the rest of the arm bones with it. The legs are set up with an Inverse
Kinematics (IK) chain, so you can position the legs by dragging the feet, and the rest of the leg bones fol-
low. By default, all CAT prebuilt rigs have stretchy bones, so if you select and move a bone, the selected and
attached bones stretch to maintain the joint connection.

Tip
If you double-click a bone, the bone and all its children are selected. For example, double-clicking a collar bone
selects the entire arm, making it easy to move the whole arm into place. n

A CAT rig keeps track of the different types of body parts and presents the appropriate set of parameters
depending on which bone is selected. For example, if you select any part of the arm, the Limb Setup roll-
outs appear in the Modify panel. This rollout has specific parameters for the arms and legs, as shown in

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