Graphics Programs Reference
In-Depth Information
IK (Inverse Kinematics)
Inverse kinematics
(IK) uses a complex set
of calculations to figure out the exact rota-
tions that need to be applied to every item
within a hierarchical system in order to
have its
puller
remain in constant contact
with its
goal
.
In practice, IK systems consist of chains
of bones. The last bone in the chain acts as
the
puller
for those higher up. The puller
bone uses a
goal
object with which it strives
to remain in contact. The goal is typically a
null
object, although it can be any object
you choose.
Note
Not all IK is created equal!
IK requires very precise calculations in
order for it to work
dependably
. In this,
LightWave's floating-point mathematics
engine (which keeps its calculations accurate
to many, many places to the right of the dec-
imal point) makes it one of the best
packages available for character animation.
Don't be fooled. Other software may have
great salesmen, but LightWave has got it
where it counts. It is
dependable
and
predict-
able
in every situation. Thanks to
LightWave's robust IK, I was able to do
nearly ten times the amount of feature-qual-
ity animation per day as is expected from
feature animators using other packages.
What Is IK?
IK allows the animator to focus on the
broad strokes of a pose or gesture while the
IK solver handles many of the small but
important details. Using IK, you simply
pose a character's hand control, and the
character's arm bones do what they need to
do to remain in contact with the hand's
base.
Figure 16-3: IK in action driving the positioning for
a character's arm.
“Standard” IK Basics
Let's take a look at the basics of “standard”
IK. I'm saying “
standard
” here because
LightWave 8's new IK Booster tool (which
we'll discuss shortly) provides a system
that is as much of an advancement on IK as
IK
itself
was on character animation back in
the early '90s. I've found that IK Booster
works best when it's used as a supplement
to standard IK, so we'll begin by laying the
groundwork for how a traditional IK system
works and how it is set up.
Figure 16-2: Inverse kinematics. With IK, you set
the hand as the puller for the chain of bones and
the null as the puller's goal, and the bicep and
forearm automatically figure the perfect set of
rotations that will keep the puller's base at the
exact location as the goal's base.
