Virtual Character Definition and Animation within the MPEG-4 Standard - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 36

composition of elementary rotations, namely twisting, abduction and flexion.
Here, 296 angular joint values are enough to describe any 3D posture of a virtual
human-like character. The angular values are specified with respect to the local
3D coordinate system of the anatomical segment. The origin of the local
coordinate system is defined as the gravity centre of the joint contour common
to the considered anatomical segment and its parent. The rotation planes are
specified and/or anatomical segment rotation axes are standardized. Contrary to
BDPs, BAPs are meant to be generic, i.e., independent of, or poorly dependent
upon, the avatar geometry.
Figure 4 and Figure 5 illustrate the rotation axes for arm, forearm and fingers.
For a complete definition of the axes associated with all body segments, one is
referred to ISOIEC (2001).

Figure 4. Standardized rotation axes attached to shoulder, elbow and
wrist.

(a) (b)