9

Setting Precedence Manually (HD Solver) 471
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
chainonajoint-by-jointbasis.Forexample:
• Animating models with a combination of
light, flexible joints and heavy, resisting joints.
Imagine a mo del of heavy iron balls linked
together w ith lengths of chain. Sett ing the
precedence va lues of the chains hig her than the
precedence values of the iron balls simulates the
balls’ inertial resistance to motion.
•Animatingamotionwherecertainjointsmust
move before other joints. Imagine a golfer’s arm
where the elbow should remain locked while
sw ing ing a golf club. You could accomplish this
by setting the precedence of the elb ow 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.
Theprecedencecalculationsonlyconsiderthe
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.
The figures show precedence values that were assigned
manually: the chain for the structure uses the b ody as the root
object and the duck as the end effector.
Terminating Chains (HD S olver)
The kinematic chain is automatically defined
using the object you select as the end effector
and working up the hierarchical tree to use the
root object as the base of the kinematic chain.
Sometimes you might not want the k inematic
chain to go all the w ay to the root of the hierarchy.
This is especially true when you are animating
multi-limbed or branching str uctures, such as an
octopus or a t ree.