2009

the entire hierarchy to a precedence of 0 and each child to a value equal to
-10 times its depth from the root.
You almost always assign Parent->Child precedence to an entire kinematic
chain. The chain for the structure in the above figure uses the body as the
root object and the duck as the end effector. Using Parent->Child precedence,
the feet are assigned a precedence of -50 and the duck is assigned a precedence
of -140.
You might want to assign Parent->Child precedence to a single object in the
kinematic chain. The value assigned to the object is equal to its depth from
the root of the hierarchy times -10.
Setting Precedence Manually (HD Solver)
Some models and animated motions don't fit neatly into a Child->Parent or
Parent->Child precedence. In such situations you can manually assign
precedence values to any object in the IK chain on a joint-by-joint basis. For
example:
■ Animating models with a combination of light, flexible joints and heavy,
resisting joints. Imagine a model of heavy iron balls linked together with
lengths of chain. Setting the precedence values of the chains higher than
the precedence values of the iron balls simulates the balls' inertial resistance
to motion.
■ Animating a motion where certain joints must move before other joints.
Imagine a golfer's arm where the elbow should remain locked while
swinging a golf club. You could accomplish this by setting the precedence
of the elbow lower than the precedence of the wrist and shoulder.
High precedence values are calculated before low precedence values. Precedence
values that are equal are calculated in Child->Parent order.
The precedence calculations only consider the relative IK values. This means
that an IK chain of three objects with precedence values of 0, 30, and 200
would have the same solution if the precedence were changed to 1, 2, and 3.
3440 | Chapter 15 Animation