9

Using IK Keyframe Parameters 901
IK group parameters
IK Blend can be set per key for any ar m or leg
track. The IK Blend setting determines whether, at
aparticularkey,anarmorlegismovingthroughit
using inverse kinematics, forward kinematics, or a
blending of the two kinematic solutions.
An IK Blend value of 0.0 means full forward
kinemat ics. The arm (or leg) is moved by
interpolating the rotations of the joints at the keys.
The hand (or foot) tends to mov e along sweeping
circular arcs in this case, and the mot ion appears
to be motivated by the apparent swinging at the
joints.
An IK Blend va lue of 1.0 means full inverse
kinematics with the hand (or foot) being used
as an end-effector. A spline path is computed
through the keys of the hand, and the hand moves
alongthatspline. Jointanglesfortherestofthe
arm a re computed to allow the hand to follow the
spline. T he motion, in this case, appears to be
directed by the hand (or foot).
An IK Blend value between 0.0 and 1.0 means a
combination of in verse and forward kinematics;
when IK Blend is closer to 0.0, forward kinematics
aremoreheavilyweightedinthesolution,and
when IK Blend is closer to 1.0, inverse kinematics
are more heavily weighted.
It is best to use forward kinematics when you want
thearmstoswing,suchaswhenabipediswalking.
Inthecaseofaboxer,however,sincethehand
should follow a directed path when punching,
inverse kinematics should be used.
To set the IK Blend value of a key:
1.
Select a single arm or leg track by selecting one
or more parts of a biped’s arm or leg.
The IK Blend spinner and the other controls in
the IK area are enabled only when a single arm
or leg track is selected.
2. Set a key if one doesn’t a lready exist.
3. Set the desired v alue of IK Blend.
Body and Object Options
By default, Biped calculates the kinematics solution
using the coordinate system of the biped figure’s
center-of-mass, or the Body coordinate system.
This means that the IK path of the hand (or foot)
translates and rotates with your character as it
moves. For example, the boxer’s hand trajectory
always moves relative to the weaving, bobbing,
and turning of the boxer’s b ody.
The Object option is used for animating dynam ic
links between the limbs and other objects in the
scene.
The IK Blend control activates when a biped arm
or leg (hand and foot) key is current.
• 0 with Bo dy turned on is forward kinema tics
(page 3–944),ornormalbipedspace.
• 1 with Body turned on is inverse kinematics
(page 3–958), creates more straight-line motion
between biped keys.
• 1 with Object turned on, but no IK object
specified, puts the limb fully into world space.