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 |
