Behavioral Animation - Computer Animation: Algorithms and Techniques - page 358

In this type of crowd, the appearance and motion of the individuals must be organized to be believable,
not distracting, and computationally efficient.
The second application of graphical crowd modeling is as a simulation of activity in a space in order
to better understand that activity. Here, the visuals are not the focus. The distribution and spatial rela-
tionship of crowd members with respect to each other and with respect to the environment are the main
concern. For example, crowd animation might be used to model the translocation of a mass of people,
such as a crowd entering an amusement park or exiting a stadium, in order to evaluate the various path-
ways through an environment for traffic flow. A related use that has received a fair amount of attention
recently is evacuation simulation. In these cases, the appearance of the individuals has no value, it is
only the location of the members and how they traverse the environment while trying to escape some
threat, such as fire, usually in a building. Here, the cognitive modeling and subsequent data gathering
are the important tasks. The visuals are either not important at all or are of secondary importance. Often
the crowd members are represented merely as dots in a bird's-eye view of a building floor plan.
11.4.1 Crowd behaviors
There are certain behaviors that individuals of a crowd assume because they are members of the crowd.
These behaviors are similar to that found in members of a flock: collision avoidance and maintaining
crowd membership. Simulating crowd behavior is both an interesting and challenging research area.
Using Reynolds' flock of boids as a reference, crowd members engage in collision avoidance, match
the velocity of neighbors, and stay close to other crowd members. For example, in finding seats in a
theater or evacuating a building, the flow of the crowd can be studied [ 16 ] . However, as opposed to
typical models of flocking behavior, crowd flow can be multidirectional. Using psychology literature
as a source for how people behave in crowds (e.g., [ 36 ]), one of the main activities found in crowds is
the avoidance of oncoming people when traversing an environment. Various rules can be derived by
looking at actual behavioral studies, as seen in the following:
￿ In high density, start avoiding at 5 feet or nearer; in low density, avoidance can start at 100 feet
￿ In low density, change paths; in high density, rotate body and side step ( step and slide )
￿ Open (front to other person, men) versus closed (back to other person, women)
￿ In changing path, move to open side else tend to move to right
￿ Avoid people moving in the same direction by slowing down or overtaking them and resuming the
original course after the pass has been completed
11.4.2 Internal structure
There are higher cognitive behaviors that create substructures within the group. While a crowd can
exhibit an aggregate behavior (e.g., so-called mob mentality ) that is similar to the flocking behavior
of birds and emerges from localized motion of the flock members, it is usually made up of smaller
groups of people in which the group members interact closely. Group membership is dynamic, and
group interaction often occurs [ 22 ] .
Groups are formed by common urges (e.g., going for lunch), belief systems (e.g., political allies),
and emotional state (e.g., soccer fans) as well as by spatial proximity. Individuals of a crowd may or