2009

solver from Bone2 to Bone4. If we parent the chain directly to world, it would
appear as shown in the right figure: the solver plane becomes horizontal.
■ A: Parent Space is Start Joint. The sphere is mounted after the rotation of
A and therefore the “horizontal plane” coincides with the chain plane as
shown in the viewport. The singular points are perpendicular to the Start
Joint with regard to the plane. When the goal/end effector is moved on
the plane, it will never hit the singular points and flip.
■ B: Parent Space is IK Goal. Again, we assume that the parent space of the
goal is the world. The “horizontal plane” of the sphere becomes horizontal,
as shown in the right figure. The singular points, the poles, are on the
plane that joints are laid out. Therefore, when users move the goal/end
effector left to right, or the other around, the end effector will move across
the singular point and flip.
A problem of B is that the figure on the right is never shown to the user. They
have to envision it in order to understand the flipping.
Example 3
This example describes what happened when Start Joint is reassigned. Suppose
we have an IK chain of four bone nodes.
Inverse Kinematics (IK) | 3405