9

IK Solver Rollout (HI Solver) 453
Example 3
This example describes what happened when Start
Jointisreassigned.SupposewehaveanIKchain
of four bone nodes.
1. Bone01
2. Bone02
3. Bone03
4. Bone04
The Start and End Joints are Bone01 and Bone04,
respectively. Suppose the p ose show n in the
figure is the preferred pose and Bone01 contains a
rotation. If we parent Bone02 directly to the world,
the hierarchy f rom Bone02 will appear as in the
right figure.
When we reassign Start J oint to Bone02, the
Zero Plane Map sphere will be based on the
configurationontheright.
• A: Parent Space is Start Joint. In this case, the
sphere that is fixed to the ri ght configuration is
to be parented to Bone01 together. This will
bethesameastheonebasedonBone01to
Bone04. Therefore, we get the same norm a l
and chain stays stationary.
• B: Parent Space is IK Goal. In this case, the
sphere stays in the world while Bone02 is
parented to Bone01. When Bone04 is moved
to where it is shown on the left due to the
transformation of Bone01, the observer who is
fixed to the sphere t hat is fixed to the world will
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 the solver/goal and assig ned a new
one from Bone02 to Bone04, you will find that the
chain won’t flip . Why? Assignment of Start Join t is
different from c reating a new IK chain/goal. Start
Joint is one of many IK parameters. Reassigning
it is simply the same as modifying any par ameter.
The rest parameters are intact. In particular, 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 particular,
the Swivel Angle will be set to a value so that the
solver plane keeps stationary in the v iewport.
HI IK Solver R ollouts
(M otion Pa nel)
IK Solver R ollout (HI S olver)
Select an HI or IK Limb Solver IK Chain control (the
blue cross at the end of the chain.) > Mo tion panel >
Parameters button > IK Solver rollout
The HI Solver is a history-independent solver
that doesn’t rely on the calculations from
previous f r ames for the IK solution, so it is fast
to use no matter the length of your animation.
The history-independent solver uses a go al 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.