Virtual Character Definition and Animation within the MPEG-4 Standard - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 51

in the node data, to the Euler angles-based representation, used in the animation
resource (file or stream), and vice versa (Shoemake, 1994).
The Inverse Kinematics information related to a bone refers to the position of the
bone in a kinematics chain and to the definition of possible movement constraints
of this one bone.
The fields of the SBMuscle node are illustrated in Figure 11b. The SBMuscle
node enables us to add information relative to local deformation for simulating
muscle activity at the skin level. Mainly two kinds of information are represented
by this node: the influence volume and the curve form. The muscle influence
volume described is supported as follows. The specification of the affected vertices
and of the measure of affectedness is performed by instantiating the vertices list
( skinCoordIndex ) and the affectedness list ( skinCoordWeight ). The influence
volume is computed by using the radius and falloff fields. The radius field
specifies the maximum distance for which the muscle will affect the skin. The
falloff field specifies the choice of the measure of affectedness function as

π

x and 4 for 3

follows: -1 for x 3 , 0 for x 2 , 1 for x , 2 for sin( x ) , 3 for

x .

2

The animation of the muscle curve is based on NurbsCurve structure as defined
in Grahn (2001) and uses the following fields: controlPoint — containing the
coordinates and the weights — and knot. The main fields of the SBSkinnedModel
node are illustrated in Figure 12.

Figure 12. The fields of the SBSkinnedModel node.