Virtual Character Definition and Animation within the MPEG-4 Standard - 3D Modeling and Animation: Synthesis and Analysis Techniques for the Human Body - page 28

animation and compression/transmission. It is shown how this framework
is extended within the new MPEG-4 standardization process by: 1) allowing
the animation of any kind of articulated model, and 2) addressing advanced
modeling and animation concepts, such as “Skeleton, Muscle and Skin”-
based approaches. The new syntax for node definition and animation
stream is presented and discussed in terms of a generic representation and
additional functionalities. The biomechanical properties, modeled by means
of the character skeleton that defines the bone influence on the skin region,
as well as the local spatial deformations simulating muscles, are supported
by specific nodes. Animating the virtual character consists in instantiating
bone transformations and muscle control curves. Interpolation techniques,
inverse kinematics, discrete cosine transform and arithmetic encoding
techniques make it possible to provide a highly compressed animation
stream. Within a dedicated modeling approach — the so-called M ESH G RID —
we show how the bone and muscle-based animation mechanism is applied
to deform the 3D space around a humanoid.
Context and Objectives
The first 3D virtual human model was designed and animated by means of the
computer in the late 70s. Since then, virtual character models have become more
and more popular, making a growing population able to impact the every day, real
world. Starting from simple and easy-to-control models used in commercial
games as those produced by Activision or Electronic Arts, to more complex
virtual assistants for commercial 1 or informational 2 web sites, to the new stars
of virtual cinema 3 , television 4 and advertising 5 , the 3D character model industry
is currently booming.
Moreover, the steady improvements within the distributed network area and
advanced communication protocols have promoted the emergence of 3D com-
munities 6 and immersion experiences (Thalmann, 2000) in distributed 3D virtual
environments.
Creating, animating and, most of all, sharing virtual characters over Internet or
mobile networks requires unified data formats. If some animation industry
leaders try — and sometimes succeed 7,8 — to impose their own formats in the
computer world, the alternative of an open standard is the only valid solution
ensuring interoperability requirements, specifically when hardware products are
to be built.
A dream of any content producer can be simply formulated as “creating once and
re-using forever and everywhere, in any circumstances.” Nowadays, content is