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902 Chapter 14: character studio
Use this to control foot sliding in a freeform
animation.
• 1 with Object turned on and an IK object
specified puts the biped limb into the
coordinate space of the selected object; the
biped limb follows the specified object.
Join To Pr ev IK Key
This IK constraint is used to specify if a footstep
isslidingorplanted.IfJoinToPrevIKKeyison,
then the biped foot maintains a reference position
to the previous key, keeping the foot planted. If
Join To Prev IK Key is off during a footstep, then
the foot can be moved to a new posit ion creating
aslidingfootstep.
Join To Prev IK Key also functions to lock the
biped hands in space. Use S et Planted Key on the
bipedhandstolocktheirpositioninspace.
Tip: If you are ha ving trouble with a foot or hand
popping back to a previous ‘keyed’ position, check
to make sure that the Join To Prev IK Key is off,
especially when you’re us ing pivot points.
See also
Key Info Rollout (page 2–954)
Understanding Walk Cycle
Constraints
Wal king motions in both freeform and footstep
animations should follow the rules of certain
IK constraints. In both freeform and footstep
animation, a footstep interval is the start and end
of a sequence of IK constraints in world space,
with IK Blend set to be greater than 0.0. A biped
foot in the Move state should have body space
turned on w ith an IK Blend of 0.0. By u sing these
IK constraints, you can convert b etween the two
animation metho ds seamlessly.
In a freeform walking animation, typically you
need two key types for the legs:
• If the foot is planted on the ground, the key
must have IK Blend=1.0 with Object Space and
Join To Prev Key turned on.
• If the foot is in the air between footsteps, then
IK Blend=0.0 with Body Space turned on, and
Join To Prev Key turned off.
In the course of creating a walk or run cycle, you
need to alternate these IK constraints for the feet.
If the foot is sliding on the ground, then the IK
constraints are IK Blend=1.0 in Object Space
w ith Join To Prev Key tuned off. All of these IK
parameters can be found on the Key Info rollout.
To speed up the process of applying these
IK constraints, the Key Info rollout has three
additional set key buttons: Set Planted Key, Set
Sliding Key, and Set Free Key. By clicking one of
thesebuttons,allthenecessaryIKconstraintsare
applied automatically. For example, by clicking Set
Planted Key, all of the IK constraints necessary are
applied at once; IK Blend=1.0 w ith object space
and Join To Prev Key turned on.
See also
Key Info Rollout (page 2–954)
Wa lkin g Keys
Let’s examine the IK constraints for one footstep.
The footstep rolls on the heel of the foot, then
rotatesdownflatontheground,thenraisesupon
the ball of the foot, rotates at the end of the toes,
and finally lif ts off of the ground.