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454 Chapter 12: Animation
The preferred angle can also b e considered as the
initial angle; that is, the angle at which the link was
rotated at the time the solver was applied.
The IK solution takes place in a plane, kno wn as
the solver plane. The angle of t he solver plane is
controlled by a p ar ameter called the swivel angle.
Changing the swivel angle
The angle of the solver plane is actually calculated
in one of two coordinate systems: the Start Joint
Parent space or the IK Goal Parent space. World
space is not an explicit option; however , you can
easilyconfiguretheIKchaintoworkinworld
space by choosing the IK Goal Parent option and
making sure that the IK goal is unlin ked (i.e., has
no hierarchical parent). In this case, the IK goal’s
parent is the world, and therefore, the solver plane
wi ll be computed in world space.
The swivel angle is animatable. You can adjust it
directly, or with a manipulator. Or you can target
the swivel angle to a object and animate that to
affect the swivel angle. These parameters are on
the IK Solver Properties rollout (page 2–456).
The HI Solver is designed to let the animator
jump back and forth between forward and inverse
kinematics quickly and conveniently, with tools to
automatically enable IK and snap the goal to the
end effector.
Procedures
To turn off IK on a chain:
1.
SelectthegoalofachainwithanHISolver.
2. In the Motion panel IK Solver rollout, turn off
Enabled.
IK is now off, so you can select and rotate any
of the objects in the chain. Turning IK on and
off is animatable using the Auto Key button.
To mix IK and for ward k inematics (FK) in a single
animation track:
1.
ApplyanHIIKSolvertoahierarchyorbone
system.
2. Turn on the Auto Key button and move the
time slider ahead in time.
3. Selec t the go al of the IK Chain, and open t he
Motion panel.
4. Select and move the goal to animate the IK
chain with Inverse Kinematics.
5. Advance the time slider again.
6. In the IK Solver Rollout, turn off Enabled and
IK for FK Pose.
7. Select and rotate the root. The entire hierarchy
rotates freely. You are now adding keyframes
using forward kinematics.
To match the goal and the end effector positions:
1.
If the goal and end effector become separated,
click IK/FK Snap and the goal will move to
match the end link of the chain.
2. If A utoSnap is turned on, clicking the goal
wi ll automatically perform the snap action,
matching the goal and end effec tor positions.