Briefly, the rules are:

1. Seperation : Boids try to fly towards the centre of mass of neighbouring boids. This is done to avoid crowding local flockmates.




Fig 1. seperation of boids

2. Cohesion : Boids try to keep a small distance away from other objects (including other boids). Boids steer to move toward the average position of local flockmates.



Fig 2. cohesion of boids

3. Allignment : Boids try to match velocity with near boids. So boids steer towards the average heading of local flockmate.



Fig 3. allignment of boids

Each boid has direct access to the whole scene's geometric description, but flocking requires that it reacts only to flockmates within a certain small neighborhood around itself. Flockmates outside this local neighborhood are ignored.

In the boids model interaction between simple behaviors of individuals produce complex yet organized group behavior. The component behaviors are inherently nonlinear, so mixing them gives the emergent group dynamics a chaotic aspect. At the same time, the negative feedback provided by the behavioral controllers tends to keep the group dynamics ordered. The result is life-like group behavior.