2009

Assume this is the pose when the IK solver is assigned. So, this is the preferred
pose. The plane on that the joints are laid out is the horizontal plane of the
(Zero Plane Map) sphere.
■ A: Parent Space is Start Joint. In this case, the sphere is parented to A. If A
is rotated about the drawn axis, the sphere is rotated together with it. The
goal is in a separate transformation hierarchy. It stays in place, and the
end effector sticks to it because of the IK solution. Since the (plane) normal
is fixed to the sphere, it rotates with A, too. Therefore, the whole chain
appears to be rotated together with the parent object.
■ B: Parent Space is IK Goal. Suppose that the goal is parented to the world.
In this case, the sphere is parented to the world and, hence, stays fixed.
Since the normal is fixed to the sphere, the chain will appear stationary
when A is rotated.
Example 2
In the following example, we look at a case where there exists a rotation in
the parent space when the IK solver is assigned.
The parent space of the IK chain contains a rotation when the IK solver is assigned.
Parent A contains a rotation of 90 degrees. This is an abstraction of the case
when a user creates four bones without an IK solver and later assigns an IK
3404 | Chapter 15 Animation