1 Introduction
Virtual worlds are ubiquitous in video games, training applications and animation films. Such worlds, to become more lively and appealing, are populated by a large number of characters. Typically, these characters should be able to navigate through the virtual environment in a human-like manner, avoiding collisions with other characters and the static part of the environment. As a result, a realistic and physically correct simulation of virtual humans has become a necessity for interactive worlds and games.