Interactive and Controlled Synthesis of
3D Irregular Shapes
Laurent Moccozet and Prem Kalra
Abstract
This chapter presents interactive methodology for 3D design of irregular surfaces. The surfaces are
polygonal and used for modeling synthetic actors. The methodology described addresses issues such as
direct surface manipulation, surface polygon-resolution control, and adaptation for animation. Direct
manipulation is based on primitive operation where primitives like vertices, edges and triangles are
accessed directly for performing a desired operation. Polygon-resolution control of the surface provides
the possibility of changing the number of polygons of the surface while preserving its shape-features.
The final surface created is used for a particular situation of animation. Example of facial animation is
included to illustrate the application of the underlying design approach.
1. Introduction
There have been many surface representations for modeling 3D objects for different purposes. Each
representation has some advantages and disadvantages. Among existing ways of surface representation,
polygonal meshes are widely used. The popularity of this representation comes mainly from the fact that
they can be directly handled at the hardware level by current graphics workstations, allowing to rapid
polygon drawing. Allan et al. (1989) provide an exhaustive list of advantages of this representation,
particularly with reard to irregular shapes. Any object can be modeled using polygons, and any other
representation can be converted to a polygonal mesh. Efficient rendering algorithms can render solids as
wire-frame for previewing or ray-traced for final rendering. However, there exist some inherent
disadvantages of the above choice, for it being polygon-based (Allan et al. 1989). Still, in the context of
constructing irregular shapes such as synthetic actors, we have found polygonal surface representations
to be appropriate.
3D construction/design of objects fundamentally involves natural and intuitive interaction. One of