To determine if there is a threat of collision with a visible fish we introduce a collision sensitivity region. It works in a similar manner as the antenna ray used above. A collision sensitivity region is a region of wherein any object intersecting with it is considered to present a collision threat. The different sizes of the sensitivity region associated with different fishes can result in different `disposition': a large sensitivity region results in a `timid' fish that takes evasive action to avoid a potential collision well in advance, while a tight sensitivity region yields a `courageous' fish that takes evasive action at the last second.
Let the center line of a fish be the line through the mean positions of the following sets of nodes: (see Fig. ; larger fishes need a finer sampling and this is done by interpolating the center line). For efficiency we choose to represent the collision sensitivity region as a rectangular box, see Fig. . Fish i presents a threat of collision to fish k if any node on i's center line falls within k's collision sensitivity region. The size of a fish's collision sensitivity region may be varied according to behavioral needs, as will be seen in the next chapter. If more than one other fish present a collision threat, the one with the largest portion of its center line in fish i's sensitivity region is regarded as being the most dangerous.
Figure: The fish's collision sensitivity region.
|Xiaoyuan Tu||January 1996|