Group Behaviors
Seminal flocking papers
Craig Reynolds
• Flocks, Herds, and Schools: A Distributed Behavioral
Model – SIGGRAPH 1987
• Steering Behaviors for Autonomous Characters
• MIT BS and MS
• Oscar awarded in 1998
• EA, Dreamworks, Sony Playstation
Components of flocking
Three factors influence acceleration
• Move closer to centroid of local neighbors
• Avoid collisions with closest neighbors
• Maintain same velocity as neighbors
Boid details
Some physics
• f = ma
• Banking (when turning) is modeled
Some logic
• Averaging acceleration urges leads to problems
– Do nothing when two vectors cancel
• Prioritized allocation of movements to acceleration urges
– Flock centering could be ignored to avoid an obstacle
Components of flocking
Local perception of neighbors
• Reduces computational complexity
– n2 in number of boids otherwise
• Improves realism
– React to what you know
– Mistakes will happen
Local perception of neighbors
Xiaoyuan Tu
• Artificial Fishes: Autonomous Locomotion, Perception, and
Behavior, SIGGRAPH 1994 with Demetri Terzopoulos
• Movies
– Go Fish!
– The Undersea World of Jack Coustou
• Awards
– Only woman ever to win the ACM dissertation award
 First Chinese (Tsinghua) and first from Canada as well!
Other sources for group
dynamics
Helbing et al. – Trails
Robotics
• Maja Mataric
• Ron Arkin
Helbing et al. – Escape Panic