Graphics Reference
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be generated. Accurately positioning the resulting textures requires the generation of texture coordi-
nates [ 56 ] . The skin may be simulated using complex physically based simulations [ 25 ] [ 44 ] . Wrinkles
may also be simulated by various means [ 47 ] [ 60 ].
9.1.5 Layered approach to human figure modeling
A common approach to animating the human figure is to construct the figure in layers consisting of
skeleton, muscles, and skin. The skeletal layer is responsible for the articulation of the form. The mus-
cle layer is responsible for deforming the shape as a result of skeletal articulation. The skin is respon-
sible for carrying the appearance of the figure.
Chadwick et al. [ 13 ] introduced the layered approach to figure animation by incorporating an artic-
ulated skeleton, surface geometry representing the skin, and an intermediate muscle layer that ties the
two together. The muscle layer is not anatomically based, and its only function is to deform the surface
geometry as a function of joint articulation. The muscle layer implements a system of FFD lattices in
which the surface geometry is embedded. The lattice is organized with two planes on each end that are
responsible for maintaining continuity with adjoining lattices, and the interior planes are responsible
for deforming the skin to simulate muscle bulging ( Figure 9.1 ). As the joint flexes, the interior planes
elongate perpendicular to the axis of the link. The elongation is usually not symmetrical about the axis
and is designed by the animator. For example, the upper-arm FFD lattice elongates as the elbow flexes.
Typically, the FFD for the upper arm is designed to produce the majority of the skin deformation in the
region of the biceps. A pair of FFD lattices is used on either side of each joint to isolate the FFDs
responsible for muscle bulging from the more rigid area around the joint. In addition, the joint FFDs
are designed to maintain continuity on the outside of the joint and create the skin crease on the inside of
the joint (see Figure 9.2 ) .
Artistic anatomy can be used to guide analysis of the human form [ 57 ] [ 58 ] [ 66 ]. Bones, muscles,
tendons, and fatty tissue are modeled in order to occupy the appropriate volumes. Scheepers [ 57 ] iden-
tifies the types of muscles sufficient for modeling the upper torso of the human figure: linear muscles,
leading deform
trailing deform
y
x
link axis
z
0
12
3
4
5
6
midplanes
adjoining planes
FIGURE 9.1
The basic FFD lattice [ 13 ] .
 
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