IK(Inverse Kinematics) on Maya

IK avoids the tediousness of specifying motion with forward kinematics.

Adding IK handle(Skeleton>IK Handle Tool): create chain of joints -> select end effector and top node.

Preferred angle of joints: initial rotation of joints for IK poses; set upon creation of chains, or can be later modified by Skeleton>Set Preferred Angle; set to non-zero angles for most bending joints to obtain desired motion.

Attaching skin geometry to joint:

- Insert it into the joint hierarchy (make sure to change pivot accordingly), or

- Bind it to desired joint:

1. Smooth bind (Skin>Smooth Bind):
   • Skin weight can be painted so that it deforms smoothly relative to adjacent joints' transformation (RM on joint -> Paint -> cluster -> weight)
   • Influence objects can be used for more customized transition (Skin>Edit Smooth Skin>Add Influence). Use Set Driven Key window (Animate>Set Driven Key>Set) to link and key in motion relationship between joint and object.
2. Rigid bind (Skin>Rigid Bind):
   • Make use of flexor (Skin>Edit Rigid Skin>Create Flexor) to control skin transformation at joints, such as creasing, rounding, etc.

Constraints: joints can be attached and constrained relative to a geometry object (and vise versa); weight controls how much one sticks to the other -- can be keyed to generate desired animation.

Spline IK handle: used to animate smoothly varying chain of joints such as spine and tail (Skeleton>IK Spline Handle Tool); create chain of joints -> select start and end joint; animated by adjusting the curve.