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438 Chapter 12: Animation
that you specify as a terminator for the chain. The
kinematic chain is defined when you apply an IK
solver to a chain, or when you create a bone chain
w ith an IK solver automatically applied.
Goal—The goal is used by the HI Solver to
manipulate the end of th e chain. When the goal is
animated, the IK solution attempts to match the
end effector (pivot point of the last child in the
chain) to the goal position. When using an HD
Solver, the end effector f ulfills the sam e fun ction
as the goal.
End Effector—For any IK solution, you explicitly
move a control object . IK ca lculations then move
and rotate all other objects in the kinematic chain
to react to the object you move. The object that
you move is the goal, in an HI Solver or IK Limb
Solver, or in the case of an HD Solver, an end
effector (page 3–933).
Prefer r ed Angl e—Determines which direction a
jointwillbend.Thepreferredangleestablishesa
base angle between chain elements w hen an HI
Solver is applied. The IK Solution seeks this angle
in calculations.
Solver Pla ne a nd Swivel Angle Manipulator—A
plane can b e defined between the start and end
joints, which aids in cont rolling the IK s olution.
Adjust or animate the solver plane by changing
the swivel angle manipulator w hen in manipulate
mode. Thisdeterminesanup-vectorhandlefor
the chain, which can also be anim ated over time.
You can also define a target for the swivel angle
manipulator to follow. For more information, see
White Paper: S wivel Angle of the HI IK Solver (page
2–449).
Terminators—You can explicitly set the base of an
HD (History -Dependent) IK chain by defining
one or more objects as terminators. A terminator
object stops the IK calculations so that objects
higherupthehierarchyareunaffectedbythe
IK solution. Terminator objects are als o used to
define hierarchies that use multiple HD IK chains.
Terminat or objects ar e not used in HI Solvers or
IK Limb Solvers. In these cases the termination is
determined by the end joint of the chain.
Bound Objects—Objectsinyourhierarchycanbe
bound to the world, or they can be bound to other
objects called follow objects (page 3–943).
Bindingallowsobjectsinyourhierarchytobe
influencedbyobjectsthatarenotpartofthe
hierarchy.
• An object bound to the world will attempt to
maintain its current position and or ientation.
• An object bound to a follow object will attempt
to match the position and orientation of the
follow object.
•Youcanbindtoafollowobjectwhenyouuse
an HD Solver, or when Applied IK is used.
Ifyouwanttobindtoafollowobjectwhen
using an H I or IK Limb Solver, apply a position
constraint between the goal and any follow
object of your choice (usually a point, dummy,
spline, or bone).
Enabled IK —(HI S olver) When using the HI Solver,
you can animate with either inverse kinematics
orforwardkinematics(FK).WhenEnabledis
turned on, inverse kinematics controls the chain,
and keyframes are placed only on the goal. When
Enabledisturnedoff,forwardkinematicrotational
keysareplacedonallthebones.
IK /FK S nap—(HI S olver) When using the HI Solver,
if you animate using both IK and FK, you might
create a situation where the goal has moved away
from the end of the chain, causing a jump in the
animation. Pressing IK/FK Snap will result in
the goal being moved back to match the posit ion
of the end effector, eliminating the jump in the
animation.