9

Inverse Kinematics (Biped) 959
• Joints are constrained with specific positional
and rotational properties.
• Position and orientation of parent objects is
determined by the position and orientation of
child objects.
Because of these added constraints, IK requires
greater thought about how you link your objects
and place pivots. Where many different solutions
for linking objects m ight be suitable for forward
kinematics, there are usually just a few good
solutions for an y given IK approach. The best
solution depends on consideration of both the
nature of the hierarchy, and how that hierarchy
will be animated.
Inversekinematicsisofteneasiertousethan
forward kinematics and you can quickly create
complex motions. However, you sacrifice some of
your control to the automation of the IK functions.
Inver se K inematics (Biped)
When you work with a biped (page 2–843),you
can use inverse kinematics (IK) by moving the
hands or feet in f reeform animation (page 3–945).
Forexample,youcanpositionanarmbymoving
the hand.
A biped has three inverse kinematics parameters
that you can vary during the limb’s motion by
setting them at e ach key of the arm and leg tracks.
As the limb moves through each key:
•
IK B lend—Sets the motion interpolation to be a
blend of forward and inverse kinematics. This
will allow you to blend swinging motions with
directed hand or foot motions. The default is
0.0, or full for ward kinematics.
•
Body or Object—Determines the reference
coordinate space (page 3–924) of the IK path.
This allows you to move the IK path with your
character’s b ody, or temporarily attach a hand
orfoottofollowanotherobjectorbeattached
to world space. The default is Body.
•
Join to Pr evious IK K ey—Determines if the key
should be part of the previous key (with the
same reference position as the previous key).
These controls are in the IK section of the Key Info
rollout (page 2–954).
Iso Line
IsolinesonaNURBSsurface
Iso is short for isoparametric.
In NURBS modeling, a line of constant p arameter
value, simi lar to a contour line. You can use iso
lines to display a NURBS surface. You can also
create dependent NURBS curves based on a
surface’s U-dimension or V-dimension iso lines.