Advances in Vision-Based Human Body Modeling - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 3

study of kinematics, the dynamics of articulated structures, etc). In the current
work, topics such as motion tracking and recognition and human body coding
standards will be particularly treated due to their direct relation with human body
modeling. Despite the fact that this survey will be focused on recent techniques
involving HBMs within the computer vision community, some references to
works from computer graphics will be given.
Due to widespread interest, there has been an abundance of work on human body
modeling during the last years. This survey will cover most of the different
techniques proposed in the bibliography, together with their advantages or
disadvantages. The outline of this work is as follows. First, geometrical primi-
tives and mathematical formalism, used for 3D model representation, are
addressed. Next, standards used for coding HBMs, as well as a survey about
human motion tracking and recognition are given. In addition, a summary of some
application works is presented. Finally, a section with a conclusion is introduced.
3D Human Body Modeling
Modeling a human body first implies the adaptation of an articulated 3D
structure, in order to represent the human body biomechanical features. Sec-
ondly, it implies the definition of a mathematical model used to govern the
movements of that articulated structure.
Several 3D articulated representations and mathematical formalisms have been
proposed in the literature to model both the structure and movements of a human
body. An HBM can be represented as a chain of rigid bodies, called links ,
interconnected to one another by joints . Links are generally represented by
means of sticks (Barron & Kakadiaris, 2000), polyhedrons (Yamamoto et al.,
1998), generalized cylinders (Cohen, Medioni & Gu, 2001) or superquadrics
(Gavrila & Davis, 1996). A joint interconnects two links by means of rotational
motions about the axes. The number of independent rotation parameters will
define the degrees of freedom (DOF) associated with a given joint. Figure 1
( left ) presents an illustration of an articulated model defined by 12 links (sticks)
and ten joints.
In computer vision, where models with only medium precision are required,
articulated structures with less than 30 DOF are generally adequate. For
example, Delamarre & Faugeras (2001) use a model of 22 DOF in a multi-view
tracking system. Gavrila & Davis (1996) also propose the use of a 22-DOF
model without modeling the palm of the hand or the foot and using a rigid head-
torso approximation. The model is defined by three DOFs for the positioning of
the root of the articulated structure, three DOFs for the torso and four DOFs for