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the entire hierarchy to a precedence value of 0 and each child to a value equal
to 10 times its depth from the root.
You almost always assign Child->Parent precedence to an entire kinematic
chain. The chain for the structure in the figure uses the body as the root object
and the duck as the end effector.
Each object receives a value equal to its depth from the root of the hierarchy
times 10. Note that precedence value calculation is based on the root of the
hierarchy whether or not the root is selected as part of the kinematic chain.
You might want to assign Child->Parent precedence to just a single object in
the kinematic chain. For example, if you have been manually changing
precedence values, you might want to set an object to its original Child->Parent
value. The value assigned to the object is equal to its depth from the root of
the hierarchy times 10.
Choosing Parent-to-Child Precedence (HD Solver)
Parent->Child precedence causes joints closest to where a force is applied (the
end effector) to move less than joints farther away from the force. This is the
opposite of Child->Parent precedence. Parent->Child precedence assigns the
highest precedence to the base object and the lowest precedence to the end
effector.
You might use this type of precedence for a number of special cases. For
example:
■ When joints near the end effector are less flexible than joints near the
base. You use Parent->Child precedence in conjunction with limits and
damping. For more information about the latter two, see
Setting Joint
Resistance and Spring Back
on page 3432.
■ When animating a kinematic chain where the real-world object is moved
by applying force to the base of the chain. Imagine an animal's tail. Using
IK you animate the tail by moving the tip of the tail. However, a real animal
moves its tail using muscles at the tail's base. The real-world motion is
applied from the base to the tip in a Parent->Child order.
3438 | Chapter 15 Animation