8

Choosing Parent-to-Child Precedence (HD Solver) 451
kinematic chain (default precedence uses the
value of 0 for every object). Child
>Parent
precedence is more flexible if you want to go back
and manually change precedence values.
The first figure shows values for child-to-parent precedence.
Assigning Child->Pa rent Pr ecedence
Clicking Child >Parent sets joint precedence
based on a child hav ing a higher precedence than
itsparent.Thevaluesarecalculatedbysettingthe
rootoftheentirehierarchytoaprecedencevalue
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 struc t ure 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 mig ht want to assign Child->Parent
precedence to just a single object in the kinematic
chain. For example, if you have b een manually
changing precedence values, you might want to set
an object to its ori ginal Child->Parent value. The
value assigned to the object is equal to its depth
from the root of the hierarch y times 10.
Choosing Par ent-to-Chil d
Pr eced ence (HD Sol ver )
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.
Youmightusethistypeofprecedencefora
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 t he latter two, see
Sett ing Joint Resistance
and Spring Back (page 2–448)
.
• Whenanimatingakinematicchainwherethe
real-world object is moved by applying force to
thebaseofthechain.Imagineananimal’stail.
Using IK you animate the tail by moving the t ip
ofthetail.However,arealanimalmovesitstail
usingmusclesatthetail’sbase.Thereal-world
motion is applied from the base to the tip in a
Parent->Child order.