For a few years, sequences of 3D meshes varying through time, which are often
called dynamic meshes, have become more and more popular in the industry, e.g.
in the entertainment area. These dynamic meshes need to be analyzed and stored
for various applications, the first of them being compression and transmission
since the amount of data quickly becomes huge (a 10 second-sequence with a
frame rate of 30 images per second contains 300 meshes !).
In the MPEG-4 standard, the coding of dynamic meshes uses 3D mesh coding
(3DMC) for the first mesh and Interpolator Compression (AFX-IC) for the
animation part. The few works that deal with compression or transmission of
sequences of 3D meshes mainly focus on multiresolution analysis [1,2].
However, these approaches often have strong requirements about the mesh
sequence: for instance, each mesh should be semi-regular or have a given
connectivity.

Objectives
This thesis explores another approach. As explained by Lengyel as early as
1999 [3], if the first mesh of the sequence (or a set of “base” meshes) is
segmented into smaller submeshes whose motion can be easily described, for
instance as rigid-body, it is necessary only to specify the affine transform for
each part instead of the motion of each vertex. For example when we deal with
character animation, the possible motion is restricted and the segmentation
should approximately correspond to the character anatomical structure: for
instance, all vertices related to a given forearm should move the same way,
since this arm can be considered as rigid.
The goal of this thesis is to propose new ways to segment dynamic meshes
without temporal coherency (that is to say, there is no bijection between
vertices of the mesh at time t and vertices of the mesh at time t+dt), which
allows efficient compression and transmission. The proposed segmentation
method(s) will use visual perception criteria to enhance compression.
The main objectives of this PhD thesis are:
The design of segmentation method(s) for dynamic meshes without temporal
coherency.
The design of compression and transmission scheme(s) for these methods.
The evaluation of these schemes using visual perception criteria.