ABSTRACT
The objective of this chapter is to present an easily programmable technique for solving the collision problem when working with a dynamic particle model of cloth. The idea is to develop a general solution applicable both to contact of fabric with external objects and to cloth self-intersection. Particular attention is given to difficult cases, such as cases involving multiple contacts (several layers of fabric) or sliding (two surfaces permanently in contact during the motion). The following issues have received prominent attention during the development of the collision detection ideas:
The dynamic-particle method is physically based and must provide a realistic response to the highly nonlinear problem of cloth drape and manipulation. The results obtained must agree with both experimental and theoretical results. The model must demonstrate stability with a wide range of possible parameters, considering both material properties and external loads. The collision algorithm must not interfere with the physical behavior of the network by creating local instabilities or constraining the natural evolution of the fabric shape.
198The base geometric element for the collision-detection algorithm is the triangle. Every surface involved in the simulation (deforming objects or fixed objects of the scenery) can be conveniently triangulated by wellknown methods. Thus, the collision method is the same for collisions throughout the environment.
Simulation time can be dramatically affected by the introduction of collision detection. The search that detects colliding parts of the deforming structure must be performed at every simulation step and must check every possible colliding configuration. Methods must be introduced that keep the time spent doing this testing to a minimum.
The collision-detection algorithm has to be implemented with the possibility of dissipative effects, including viscous effects or Coulomb friction.
