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470 Chapter 12: Animation
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 ori ginal Child->Parent va lue. The
value assi gned to the object is equal to its depth
from the root of the hierarchy t imes 10.
Choosing Par ent-to-Child
Pr ecedence (H D S olv er )
Parent->Child precedence causes joints closest
to where a force is applied (the end effector) to
move less than joints far ther away from the force.
ThisistheoppositeofChild->Parentprecedence.
Parent->Child precedence assigns the highest
precedence to the base object and the lowest
precedence to the end effector.
Youmightusethistypeofprecedencefora
number of special cases. For example:
• When joints near t he end effector are less
flexible than joints near the base. You u se
Parent->Child precedence in conjunction with
limits and damping. For more information
about the latter two, see Setting Joint Resistance
and Spring Back (page 2–466).
• Whenanimatingakinematicchainwherethe
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
ofthetail.However,arealanimalmovesitstail
using muscles at the tail’s base. The real-world
motion is applied from the base to the tip in a
Parent->Child order.
The figure show s values for parent-to-child precedence.
Ass igni ng Pa r ent->Chi ld Pr ecedence
Clicking Parent->Child sets joint precedence
based on a child having a lower precedence than
its parent. The values are calculated by setting the
root of the entire hierarchy to a precedence of 0
and each child to a value equal to -10 times its
depth from the root.
Yo u a l m o s t a l w a y s a s s i g n P a r e n t - > C h i l d
precedence to an entire kinematic chain. The
chain for the st ructure in the above figure uses the
bodyastherootobjectandtheduckastheend
effector. Using Parent->Child precedence, the feet
areassignedaprecedenceof-50andtheduckis
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 t imes -10.