To determine if some point *P* is visible, we shoot a ray from the
cyclopean origin *O* (on and near the fish's mouth) to *P* (see
Fig. ). First, if and the angle
between the ray and the fish's *x*-axis is less than 150 degrees then
*P* is within the view volume. Second, to examine if *P* is occluded, we
test if the ray intersects other objects (fishes or static obstacles)
in the fish's view volume.

Xiaoyuan Tu | January 1996 |