8

1038 Glossary
viewports. The footstep position and orientation
in the viewport controls where the biped will step.
In Track View — Dope Sheet, each footstep
appears as a block that represents a support
period in t ime for each of the biped’s feet. Moving
footstepsintimeisdoneinTrackView—Dope
Sheet.
Tip: To see the footsteps, you must turn on
Edit Keys in the Dope Sheet.
There are three ways to create footsteps for
thebiped. Thefirstwayistoplacefootsteps
individually, o ne at a time. The second way
is to invoke Biped’s multiple footstep creation
toolstocreateawalk,run,orjumpanimation.
Thethirdwayistoextractfootstepsfromraw
motion-capture data.
A big advantage of t he footstep method is the
natural adaptation of the biped that occurs when
thefootstepsareeditedintimeandspace.Also,
you can reposition al l of the footsteps to move the
entire animation.
For wa rd Kinematics
The default method of manipulat ing a hierarchy
uses a technique ca lled “forward kinematics”. The
basicprinciplesemployedbythistechniqueare:
• Hierarchical linking from parent to child
• Placement of pivot points to define the
connecting joint b etween linked objects
• Inheritance of position, rotation, and scale
transforms from parent to child
In for ward kinematics, when a parent object
moves, its children must follow. If the child wants
to go off on its own, the parent remains behind.
For example, in a hierarchical lin kage of a human
figure, when the torso (the parent) bends over, t he
head (the child) moves along with it, but you can
turn the head without affecting the torso.
Forward Ki n e m at ics ( Bi pe ds)
Usinganarmtomoveahandisanexampleof
for ward kinematics. Using the hand to move the
arm is an example of
inverse kinematics (page
3–1052)
.Whenyouuse freeform animation (page
3–1039)
to animate a biped (page 2–701) ,youcan
use both kinds of k i nematics.
By planting a hand or foot, you use another object
(object space) or the world (world space) to
control IK motion. In this method, the IK Blend
parameter in the
Key Info rollout (page 2–809)
determines how forward kinematics and inverse
kinematics are blended to interpolate intermediate
positions.
Fr ame Rat e
The f rame rate of an animation is generally
expressed in frames per second (fps). This is t he
number of frames displayed for ever y second of
real time.
Different recording devices output different frame
rates, but the st andard rates are as follows:
NTS C vid eo—30 frames per second
PAL video—25 f r ames per second
Film—24 frames per second
You can change the frame rate for your output at
any time, outputting the correct number of frames
to maintain the correct playback speed for your
animation.
For example, if you create a 90-frame animation
for video, using an NTSC frame r ate of 30 frames
persecond,theresultwillbethreesecondsof
animation.