8

IK Terminology 419
use IK solvers. Not all of the following parameters
are used by all the systems.
IK Solvers—An IK solver applies an IK solution to a
kinematic chain. The kinematic chain is composed
of a bones system, or a set of linked objects.
Joints—An IK joint controls how an object
transforms with respect to its parent. You specify
joint behavior with settings in three categories:
•
Object Pivot Point—Thelocationofanobject’s
pivotpointdefineswherejointmotionis
applied.
•
Joint Parameters—Changing the IK settings in
the Hierarchy command p anel determines the
direction, constraints, and order of how the
joint operates.
•
Par ent Pi vot Point —The location of an object’s
parent pivot point defines the origin from
which the joint constraints are measured.
The commands you use to place the pivot points
for both the object and its parent are described in
Adjusting Pivots (p age 2–405) .
Sta r t and End Joints—The star t and end joints
define the beg inning and end of an IK chain
managed by the IK solver. The hierarchy of the
chain determines the direction of the chain. The
pivot point of the end joint is displayed as the end
effector, when end effector display is enabled.
K inema tic Chai n—Inversekinematicscalculatesthe
position and orientation of objects in a kinematic
chain. The k inematic chain is defined as any part
of a hierarchy under IK control. The IK chain
starts with a selected node and consists of a start
joint and an end joint. The base of the chain is
either the root of the entire hierarchy, or an object
that you specif y 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
manipulatetheendofthechain.Whenthegoalis
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 fulfills the same function
as the goal.
End Effector—F or any IK solution, y ou explicitly
move a control object. IK calculations then move
and rotate all other objects in the kinematic chain
to react to the object you move. The object that
youmoveisthegoal,inanHISolverorIKLimb
Solver, or in the case of an HD Solver, an
end
effector (page 3–1027)
.
Prefer r ed A ngle—Determines which direction a
joint will bend. The preferred angle establishes a
baseanglebetweenchainelementswhenanHI
Solver is applied. The IK Solution seeks this angle
in calculations.
Solv er Pl ane and Swiv el Angle Ma nipul ator—A
plane can be defined between the start and end
joints, which aids in controlling the IK solution.
Adjust or animate the solver plane by changing
theswivelanglemanipulatorwheninmanipulate
mode. This determines an up-vector handle for
the chain, which can also be animated ove r time.
You can also define a target for the swivel angle
manipulator to follow. For more information, see
White Paper: Swivel Angle of the HI IK Solver
(page 2–430)
.
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. Ter minator objects are also used to
define hierarchies that use multiple HD IK chains.
Terminator objects are not used in HI Solvers or
IK Limb S olvers. In these cases the termination is
determined by the end joint of the chain.