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If you are using footstep extraction with motion capture data, you often need
a freeform interval to accommodate falling or tumbling motion in the data.
The Fit to Existing option on the Motion Capture Conversion Parameters
dialog allows for a combination of both methods. Extracting footsteps from
motion capture files eliminates sliding feet, a common problem with motion
capture data.
Note that while you can add a freeform period to a footstep animation, you
cannot add a footstep period into a freeform animation. If you want to add a
footstep animation to an existing freeform, you can use the motion flow editor
to create a script that sequences the footstep with the freeform.
Inverse Kinematics
Footstep and freeform animations use the same
inverse kinematics on page
8016 constraints and extensions. This means that in a footstep animation, you
can now edit keys to change footstep duration. By definition, a footstep is the
start and end of a sequence of IK constraints in World Space with an IK Blend
value greater than 0. Deleting and inserting keys or changing IK space or IK
blending alters footstep duration.
In cases involving edits that alter the length of ballistic intervals (when a biped
is airborne), the software ensures that there is a vertical key occurring at the
lift-off and touchdown frames. This calculates the correct ballistic motion, so
vertical keys are automatically inserted if not present.
There are three types of IK keys you can create: planted, sliding and free keys.
■ Planted keys have an IK Blend of 1. They are joined to the Previous IK Key
and are in Object space, rather than Body space. Planted keys lock the foot
or hand to the ground, or to any object.
■ Sliding keys have moving IK constraints. Sliding footsteps are created if
there is a moved IK constraint occurring in the footstep interval. In a
footstep animation this means that the foot can be placed anywhere, even
though there is a footstep icon. Footstep icons can be thought of as gizmos
rather than the absolute location of a foot. Sliding keys have an IK blend
of 1, and are in object space, but are not joined to the previous IK key.
■ Free keys have an IK blend of 0, and are in body space. They are not joined
to the previous IK key. Free keys have no IK constraint.
IK constraints are implemented with a pivot-based system. This allows you to
pivot a hand or foot around a selected pivot. For example, in a walking motion
you can select a pivot on the heel of a foot and rotate the foot around it,. You
can then shift the pivot to the ball of the foot.
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