8

760 Chapter 14: Character Studio
• 1 with Body turned on is inverse kinematics
(page 3–1052)
, creates more straight-line
motion between biped keys.
• 1 with Object turned on, but no IK object
specified, puts the limb fully into world sp ace.
Use this to con trol 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 Prev IK K ey
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 position creating
aslidingfootstep.
Join To Prev IK Key also functions to lock the
biped hands in space. Use Set Planted Key on the
bipedhandstolocktheirpositioninspace.
Tip: If you are having trouble with a foot or hand
popping back to a previous ‘keyed’ p osition, check
to make sure that the Join To Prev IK Key is off,
especially when you’re using pivot points.
See also
Key Info Rollout (p age 2–809)
Understanding Walk Cycle
Constrain ts
Walking motions in both freeform and footstep
animations should follow the rules of certain
IK constraints. In both freefor m and footstep
animation, a footstep interval is the start and end
of a sequence of IK const raints in world space,
with IK Blend set to be greater than 0.0. A biped
footintheMovestateshouldhavebodyspace
turned on with an IK Blend of 0.0. By using these
IK constraints, you can convert between the two
animation methods seamlessly.
In a freeform walking animation, typically you
need two key t ypes for the legs:
• If the foot is planted on the ground, the key
must have IK Blend=1.0 w ith Object Space and
Join To Prev Key turned
on .
• If the foot is in the air between footsteps, t hen
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 s liding on the ground, then the IK
constraints are IK Blend=1.0 in Object Space
w ith Join To Prev Key t uned off. All of these IK
parameters can be found on the Key Info rollout.
To speed up the process of applying these
IK const raints, the Key Info rollout has three
additional set key buttons: Set Planted K ey, 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 2–809)
Wa lking Ke ys
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, rota tes at the end of the toes,
and finally lifts off of the ground.