Murmuration of starlings, the type of behaviour that boids was designed to simulate
Source: YouTube

Boids, a shortened version of “bird-oid object”,[1] is a computational model of flocking behaviour proposed by the computer graphics specialist Craig Reynolds in a paper published in 1987, which he first demonstrated in 1986.[2] Reynolds formally defined flocking as “polarised, non-colliding, aggregate motion”, and his fundamental idea was that rather than scripting the behaviour of each bird in a simulated flock – or fish in a shoal, or animal in a herd – their overall behaviour would emerge if every individual followed three simple rules, without anything in overall control:[2]

  • Separation: steer to avoid crowding local flockmates
  • Alignment: steer towards the average heading of local flockmates
  • Cohesion: steer to move towards the average position of local flockmates

Reynolds’ approach was a significant step forward from the traditional techniques previously used in computer animation. The first film created using his new algorithm was Stanley and Stella in: Breaking the Ice (1987), followed by Tim Burton’s film Batman Returns (1992), with computer-generated bat swarms and armies of penguins marching through the streets of Gotham City.[3]

Flocking, or Particle Swarm Optimization as it is now more formally known, has since become an area of study in several fields of research, including statistical physics, control theory and robotics.[4]

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