Graphics Programs Reference
In-Depth Information
The normal constraint is similar to the aim constraint, and its options are similar.
Using the Aim Vector setting, you specify which way is up for the object, to define the
orientation that the source should maintain. However, this setting doesn't constrain the
location of the source to the target. If you want a floating effect, use geometry and a nor-
mal constraint to get the cone to bob up and down and roll back and forth as the waves
ripple along (see Figure 9.57).
Figure 9.57
The cone now ani-
mates to float on
the water surface,
using both geom-
etry and normal
constraints.
Parent, Tangent, and Pole Vector Constraints
Three more constraints are possible in Maya: the parent, tangent, and pole vector con-
straints. A
parent constraint
constrains an object's translation and rotation to another
object by mimicking a parent-child relationship without actually parenting the objects.
This keeps objects aligned without worrying about any grouping issues. You'll have a
firsthand look at this in the exercise where you rig the locomotive later in this chapter.
Lucky you!
A
tangent constraint
keeps an object's orientation so that the object always points along a
curve's direction. This constraint is usually used with a geometry constraint or path ani-
mation to keep the object traveling along a curve pointed in the right direction, no matter
the direction of the curve.
Pole vector constraints
are used extensively in character anima-
tion rigs to keep IK joints from flipping beyond 180 degrees of motion.
Basic Relationships: Set-Driven Keys
A favorite feature for character riggers is the
set-driven key
(SDK). A set-driven key estab-
lishes a relationship for objects that lets you create controls that drive certain features of a
character or an object in a scene.
