8
Adjusting Vertical Motion 737
Grav ity a nd T iming
Inreality,thelengthoftimeaperson,animalor
insect stays in the air during a jump is based on
two fac tors:
• Howhighthecreaturejumps,whichinturnis
based on how hard the creature pushes with
its legs at the st art of the jump. The creature’s
weight has no b earing on the height of the
jump,excepttoaffectitsabilitytogiveagood
push at the start. A very light character might
be taken by the wind and thus stay in the air
longer, but that circumstance is not part of the
gravitational equation.
• Thegravitationalpulloftheplanetfromwhich
thecreaturejumps.
From these two factors, you can calculate how
longthecreaturewillstayintheair. Youcan
also perform this calculation backward; if you
know how long the creature was in the air and
the gravitational equation for the planet, you can
figure out how high it jumped.
Jump he ight increase s with time in air
character studio uses the latter method for
calculating the height of a biped’s jump. It knows
from f ootstep timing how long the biped will be in
the air, and it has a method for determining t he
“gr av itational pull” in your scene.
The default gravity setting in character studio is
based on the standard equation for ca lculating the
Earth’s gravitational pull, which is an acceleration
of approximately 32 feet/sec/sec. B ecause this
equat ion depends on an accurate measure of
distance, the biped’s height is used as a guide to
actual distances in the scene. For the purpose of
gravitational computation, the biped is considered
to be about 5’10” tall, the average height for a male
human being.
Of course, some of your characters will not be
thesameheightastheaverageman,soairborne
periods between footsteps for these characters will
appear inaccurate, with the biped jumping too
highortoolowforyourpurposes.
There are two solutions to this problem. You
can change the amount of time the character is
airborne be tween footsteps (see
Editing Footstep
Timing (page 2–727)
), or you c an accelerate
gravity with the GravAccel parameter.
Accelera ting Gr avit y
The GravAccel parameter on the
Dynamics &
Adaptation rollout (page 2–833)
alters the degree
ofgravitationalpullimposedonthebipedduring
its airborne periods between active footsteps.
The GravAccel default value is based on the
standard calculation for the Earth ’s gravity and
its effects on a man of average height. When the
GravAccel parameter is increased, the effects of
gravityaredecreased,andthebipedjumpshigher.
The GravAccel parameter can be set separately for
each biped in the scene.