Graphics Reference
In-Depth Information
CHAPTER
9
Modeling and Animating
Human Figures
Modeling and animating an articulated figure is one of the most formidable tasks that an animator can
be faced with. It is especially challenging when the figure is meant to realistically represent a human.
There are several major reasons for this. First, the human figure is a very familiar form. This familiarity
makes each person a critical observer. When confronted with an animated figure, a person readily rec-
ognizes when its movement does not “feel” or “look” right. Second, the human form is very complex,
with more than two hundred bones and six hundred muscles. When fully modeled with linked rigid
segments, the human form is endowed with approximately two hundred degrees of freedom (DOFs).
The deformable nature of the body's surface and underlying structures further complicates the model-
ing and animating task. Third, human-like motion is not computationally well defined. Some studies
have tried to accurately describe human-like motion, but typically these descriptions apply only to cer-
tain constrained situations. Fourth, there is no one definitive motion that is humanlike. Differences
resulting from genetics, culture, personality, and emotional state all can affect how a particular motion
is carried out. General strategies for motion production have not been described, nor have the nuances
of motion that make each of us unique and uniquely recognizable. Although the discussion in this chap-
ter focuses primarily on the human form, many of the techniques apply to any type of articulated figure.
Table 9.1 provides the definitions of the anatomical terms used here. Particularly noteworthy
for this discussion are the terms that name planes relative to the human figure:
sagittal , coronal ,
and transverse .
9.1 Overview of virtual human representation
One of the most difficult challenges in computer graphics is the creation of virtual humans. Efforts to
establish standard representations of articulated bodies are now emerging [ 16 ] [ 31 ] . Representing
human figures successfully requires solutions to several very different problems. The visible geometry
of the skin can be created by a variety of techniques, differing primarily in the skin detail and the degree
of representation of underlying internal structures such as bone, muscle, and fatty tissue. Geometry for
hair and clothing can be simulated with a clear trade-off between accuracy and computational
complexity. The way in which light interacts with skin, clothing, and hair can also be calculated with
varying degrees of correctness, depending on visual requirements and available resources.
Techniques for simulating virtual humans have been created that allow for modest visual results that
can be computed in real time (i.e., 30 Hz). Other approaches may give extremely realistic results by
simulating individual hairs, muscles, wrinkles, or clothing threads. These methods may consequently
also require excessive amounts of computation time to generate a single frame of animation. The
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