Graphics Programs Reference
In-Depth Information
Figure 16-18
anything else in making character setups
that do what you'd expect them to do.
While the desire to use IK on shoulder
or hip joints in order to solve for all three
axes (heading, pitch, and bank) is tempting,
I find that often (though not always) this
makes for a loose, “swively,” hard-to-con-
trol arm or leg. Most often, character
riggers will leave the bank axis to be con-
trolled manually by the animator using FK.
This lets you precisely control the position
of the elbow or knee joint just by rotating
the bicep or thigh.
So, the rule of thumb for good, solid IK
chains in character riggings is:
The topmost
item can use IK to solve for a maximum of
two rotation axes, and the child item in a
character IK chain should use IK for only one
axis.
Rotation Order
Character riggings are complex things.
Riggings use a lot of heavy-duty math that
we animators take for granted when we're
doing our jobs. Usually, we don't care
how
something works, so long as it
does
.
But, if you're curious about the more
complex details that make for a good,
dependable character rigging, this section
and the next one will fill you in on a lot of
the stuff that goes on behind the scenes.
Note
The “Rotation Order” and “Joint Compensa-
tion and Muscle Flexing” sections are mainly
for the technical directors and the heavy-
duty math-oriented folks who really want to
understand why things happen and why cer-
tain decisions are made in the crafting of
riggings. If this isn't your cup of tea, don't
worry (there won't be a quiz on this later);
just skip to the section called “Flipping.”
Note
I don't recommend using standard IK on a
bone chain consisting of more than two
joints (such as for a character's tail). It cre-
ates too many opportunities for the complex
math to give you something you neither
expect nor want. IK Booster is the tool for
the job if you have something like a tail,
tentacle, whip, or rope you need to animate.
LightWave has a fixed order in which it cal-
culates the rotation of an item:
1) Heading
2) Pitch
3) Bank
