As we stated in the beginning of this chapter, it is also important to model the basic limitations of animal perception systems. The cyclopean vision sensor is limited to a 300 degree spherical angle extending to an effective radius that is appropriate for the visibility of the translucent water. The spherical angle and the visual range define a view volume within which objects can be seen.
As we mentioned earlier, many animals in the wild possess special sensing abilities for tracking food. We model additional perceptual clues which are isotropic, such as olfactory perception (i.e. sense of smell), by expanding to a larger radius . The strengthened perceptual ability allows our artificial fish to perceive food (but not other objects) within a certain distance, even if it is out of sight. Another purpose of modeling this additional food-sensing ability is to make foraging behavior more interesting. Imagine a fish feeding on floating plankton. Due to the water current the plankton it is after may drift out of sight temporarily. Instead of forgetting about the food it had just seen and chased, the sense of smell enables the fish to continue the pursuit. Fig. illustrates the perceptual range.
The radius of the view volume should be influenced by the size of the object. An object of normal size in the distance may be too far to be seen, but this may not be the case if a much larger object is placed at the same distance. It is especially important to model this effect such that small prey fish can detect the presence of large predator fish well in advance. To this end, we associate a `size parameter' with each fish i in the animation. represents the standard size, while represents larger sizes. When is used for determining whether fish i is visible, is scaled by the size parameter (example can be found in Section ).
|Xiaoyuan Tu||January 1996|