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1. Start joint
2. End effector
3. EE axis
Solver Plane
Let’s call the plane passing all the joints the Solver Plane. When joints do not
lie on a plane, we will define it to be the plane that (A) passes the Start Joint
and End Joint and (B) is closest to the remaining joint in a certain sense.
The Swivel Angle describes the degree of freedom of the Solver Plane and it
constrains only the Start Joint.
Zero Plane Map
In order to describe the solver plane in terms of a numerical quantity, we have
to agree to what 0 means. Given the end-effector position, where is the Zero
(Solver) Plane? The Zero Plane Map takes as the argument EE Axis and produces
the normal to the zero plane.
The IK system allows individual solver plug-ins to define their own Zero Plane
Maps. When not defined, the IK system provides a default one.
3398 | Chapter 15 Animation