Excerpt

In the mid-1980s Craig Reynolds wanted to build realistic-looking animations of animals moving in groups. While it was readily possible then, given traditional animation tools, to create realistic-looking movie scenes involving one or a few birds by scripting individual trajectories, it was not practically feasible to animate an entire flock of birds in this fashion. New tools were needed that made use of ideas about how individual birds behave in a flock. In order to do so, very basic questions concerning the origin, operation, and evolution of animal groups needed to be investigated so that code could be written that produced realistic-looking flocks and herds, in motion, simulated frame-by-frame, at real-time speeds, at least if such animations were going to be useful in the movies.

On one hand, from purely biological considerations, it seems reasonable that the behavior of individual birds, in forming and participating in a flock, should be based on the local environment of the individual birds, both the physical environment (e.g., the presence of objects that must be avoided) and the social environment, composed of other birds. But how birds perceive the world, assess their situations, and take actions, involves myriad biological processes that were (and are) incompletely understood. So how might an artificial bird—a boid—be programmed to engage in perception, decision-making, and action such that its resulting behavior, and that of its peers, took the shape of a realistic-looking flock? Or, in the case of digital fish, what programmed behaviors are sufficient to produce seemingly realistic schools? Answers to these questions were not obvious when Reynolds first started working on the problem of getting modest numbers of idealized animals to self-organize in such a way that, at least to the human eye, resembled real animal groupings.

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