Graphics Programs Reference
In-Depth Information
Forward Kinematics: The Block Man
To understand skeletal hierarchy, look at the simple biped (two-legged) character made
of primitive blocks, shown in Figure 9.4. He's called Block
Man
.
(Surprise!) Each block
represents a part of the body, with gaps between the blocks representing points where the
body pivots.
Figure 9.4
The block man's
cubes arranged
The pivot of each block is placed to represent the appro-
priate joint location. For example, the shin's pivot is located
at the knee. Each block is grouped up the chain so that
the foot moves with the shin, which moves with the thigh,
which moves with the pelvis.
The hands are grouped under the arms, which are
grouped under the shoulders, and so forth down the spine
to the pelvis. The head groups under the first neck block,
and so on down the spine to the pelvis. The pelvis is the
center of the body, which is known as the
root
of the figure.
The way this figure is grouped (see Figure 9.5) represents
how the hierarchy of a character works for the most part. Each body part is attached and
becomes the child of the part above it in the chain.
Figure 9.5
Pivot placements
and grouping
