8

IK Solver Rollout (HI Solver) 435
see that Bone04 moves away from the neutral
positiondefinedbythepreferredpose. The
algorithm then applies the Zero Plane Map to
find the normal at the displaced position. It
generally is not perpendicular to the viewport.
Therefore, we will see a flip once it takes a new
Start Joint.
If you delete t he solver/goal and assigned a new
one from Bone02 to Bone04, y ou will find that the
chain won’t flip. Why? Assignment of Start Joint is
different from creating a new IK chain/goal. Start
Joint is one of many IK parameters. Reassigning
it is simply the same as mo difying any parameter.
The rest p ar ameters are intact. In p articular, the
Swivel Angle is not changed as a result of this
reassignment.
Creating a new IK chain/goal is different. Effort is
made to ensure that the joint chain stay fixed by
adjusting parameters appropriately. In part icular,
the Swivel Angle will be set to a va lue so t hat the
solver plane keeps stationary in the viewport.
HI IK Solver R ollouts
(M otion Pa nel)
IK Solver Rollout (HI Solver)
Select an HI or IK Limb Solver IK Chain control (the
blue cross at the end of the chain.) > Motion panel >
Parameters button > IK S olver rollou t
The HI Solver is a history-independent solver
that doesn’t rely on the calculations from
previous frames for the IK solution, so it is fast
to use no matter the length of your animation.
The history-independent solver uses a goal to
manipulate the end of the chain. It uses a preferred
angle that specifies a preference regarding which
direction the link will rotate: positive or negative.
The preferred angle can also be considered as the
initial angle; that is, the angle at which the link was
rotated at the time the solver was applied.
TheIKsolutiontakesplaceinaplane,knownas
the
solver plane . T he angle of the solver plane is
controlled by a parameter called the
swivel angle .
Changing the swivel angle
Theangleofthesolverplaneisactuallycalculated
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
easily configure the IK chain to work in world
space by choosing the IK Goal Parent option and
making sure that the IK goal is unlinked (i.e., has
no hierarchical parent). In this case, the IK goal’s
parent is the world, and therefore, the solver plane
will be computed in world space.
The swivel angle is animatable. You can adj ust it
directly, or with a manipulator. Or you can target
theswivelangletoaobjectandanimatethatto
affect the swivel angle. These parameters are on
the
IK Solver Proper t ies rollout (page 2–437) .
TheHISolverisdesignedtolettheanimator
jump back and forth between forward and inverse
kinematics quickly and conv eniently, with tools to
automatically enable IK and snap the goal to the
end effector.