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White Paper: Swivel Angle of the HI IK Solver 449
Controlling HI IK Precision
When you are animating with HI Solvers, if you
find the animation of the limbs is not smooth, you
should try doubling the I terations in the Solutions
group of the HI Solver Properties rollout (page
2–456). You can also try reduce the Thresholds
value to smooth the animation.
See also
IK Solver Rollout (HI Solver) (page 2–453)
White Paper : Swivel Angle of the
HI IK S olver
The f undamental requirement of H I Solver is that
thesolutionbehistory-independent:thesolution
has to be based on the goal and other incidental
parameters solely at their current states.
Swi vel A ngl e D egree of Freedom
When the positional goal is given for a single chain,
there remains an obvious degree of freedom: the
rota tion about the End Effector Axis (EE Axis).
The swivel angle is used to describe this deg ree of
freedom quantitatively.
1. Start joint
2. End effector
3. EE axis
Solver Plane
Let’s c all the plane passing all the joints the Solver
Plane. When joints do not lie on a plane, we
w i ll define it to be t he plane that (A) passes the
Start Joint and End Joint and (B) is closest to the
remaining joint in a certain sense.
The Swivel Angle descr ibes the degree of freedom
of the Solver Plane and it constrains only the Start
Joint.
Zero P la ne M ap
In order to descr ibe the solver plane in terms of
anumericalquantity,wehavetoagreetowhat0
means. Given the end-effector position, where is
the Zero (Solver) Plane? The Zero Plane Map takes
as the argument EE Axis and produces the normal
to the zero plane.
The IK system allows individual solver plug-ins
to define their own Zero Plane Maps. When not
defined, the IK system provides a default one.
TheargumenttotheZeroPlaneMapisaunit
vector to give the direction of the EE axis.
Equivalently, when the EE slides along the EE