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452 Chapter 12: Animation
The figure shows values for parent-to-child p recedence.
Ass igni ng Pa r ent->Chil d P recedence
Clicking Parent->Child sets joint precedence
based on a child having a lower precedence than
itsparent.Thevaluesarecalculatedbysettingthe
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.
You almost always assign Parent->Child
precedence to an entire kinematic chain. The
chain for the structure in the above figure uses the
bodyastherootobjectandtheduckastheend
effector. U sing 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.Thevalueassignedtotheobjectisequalto
its depth from the root of the hierarchy times -10.
S etti ng P r eceden ce Ma nua ll y (H D
Solver)
Some models and animated motions don’t fit
neatly into a Child->Parent or Parent->Child
precedence. In such situations you can m anually
assign precedence va lues to any object in the IK
chainonajoint-by-jointbasis.Forexample:
• Animating models with a combination of
light, flexible joints and heavy, resisting j oints.
Imagine a model of heavy iron balls linked
together w ith lengths of chain. Setting the
precedence va lues of the chains higher than the
precedence values of the iron bal ls simulates the
balls’ inert ial resistance to mot ion.
• 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
thantheprecedenceofthewristandshoulder.
High precedence values are calculated before low
precedence va lues. Precedence va lues that are
equal are calculated in Child->Parent order.
The precedence calculations only consider the
relative IK va lues. This means that an IK chain of
three objects with precedence values of 0, 30, and
200wouldhavethesamesolutioniftheprecedence
were changed to 1, 2, and 3.