Virtual Character Definition and Animation within the MPEG-4 Standard - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 64

hierarchical update of the reference grid points belonging to higher resolution
levels, and the computation of the vertices coordinates according to Equation
(10) is such that the mesh follows the movements applied to the reference grid.
As illustrated in Figure 15b, not all of the reference grid points have to be
animated, only those where vertices are attached to.
The benefits of specifying an animation in terms of a hierarchical reference grid
are even more pronounced when comparing this approach to animation methods
that are directly applied to the vertices, as is the case for the I NDEXED F ACE S ET
representation. This difference in complexity is illustrated by Figure 16, which
depicts the knee of the humanoid model. As one can see in Figure 16a, the

Figure 15. Bone-based animation of the reference grid of the humanoid
model.

(a) (b)

Figure 16. Snapshot of the humanoid knee during the animation. The
reference grid lines are displayed in black. The surface at the second
resolution level is displayed as a wireframe in (a) and Gouraud-shaded in
(b).

(a) (b)