Virtual Character Definition and Animation within the MPEG-4 Standard - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 35

Figure 3. Examples of standardized key-points on the face object.

(a) (b)

deforming the mesh in the vicinity of the key points (Doenges, 1997; Escher,
1998; Lavagetto, 1999).
A virtual body object is represented in the scene graph as a collection of nodes
grouped under the so-called Body node (Figure 1b).
The BDP (Body Definition Parameters) node controls the intrinsic properties of
each anatomical segment of the avatar body. It includes information related to
the avatar body representation as a static object composed by anatomical
segments (bodySceneGraph node), and deformation behaviour (bodyDefTables
and bodySegmentConnectionHint nodes) (ISOIEC, 2001). Body definition pa-
rameters are virtual character-specific. Hence the complete morphology of an
avatar can readily be altered by overriding the current BDP node. Geometrically,
the static definition of the virtual body object is a hierarchical graph consisting
of nodes associated with anatomical segments and edges. This representation
could be compressed using the MPEG-4 3D Mesh coding (3DMC) algorithm
(Taubin, 1998a) defining subpart relationships, grouped under the bodySceneGraph
node. The MPEG-4 virtual avatar is defined as a segmented virtual character,
using the H-Anim V2.0 nodes and hierarchy: Humanoid, Joint, Segment, and Site
nodes.
The BAP (Body Animation Parameters) node contains angular values and
defines the animation parameters as extrinsic properties of an anatomical
segment, i.e., its 3D pose with respect to a reference frame attached to the
parent segment. The orientation of any anatomical segment is expressed as the