Graphics Programs Reference
In-Depth Information
The Offset values create an offset on the source's Rotation attributes, tilting it one way
or another. The Up Vector setting specifies which way the cone faces when it's pointing to
the sphere.
Aim constraints are perfect for animating cameras to follow a subject, such as a car at
a racetrack.
Geometry and normal Constraints
The geometry and normal constraints constrain the source object to the surface of the tar-
get object (as long as it's a NURBS or poly mesh).
With a geometry constraint, the source object attaches at its pivot point to the sur-
face of the target. It tries to keep its own position as best it can, shifting as its target
surface changes beneath it. Again, select the target, select the source object, and choose
Constrain Geometry.
Using a geometry constraint is useful when you want to keep an object on a deform-
ing surface, such as a floating boat on a lake. Figure 9.56 shows the cone after it has been
geometry-constrained to a NURBS plane that is being deformed by a Wave deformer
(choose Create Deformers Nonlinear Wave). The cone sits on the surface as the waves
ripple through, but it doesn't rock back and forth to stay oriented with the surface.
To get the cone to orient itself so that it truly floats on the surface, you need to use a
normal constraint. Using a normal constraint rotates the cone to follow the surface's nor-
mals, keeping it perpendicular to the surface.
A surface normal is an imaginary perpendicular tangent line that emanates from all surfaces
to give the surface direction.
Figure 9.56
With a geometry
constraint, the cone
sits on the deform-
ing surface.
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