An object is ``visible'' if any part of it enters the view volume and
is not fully occluded by another object. To determine visibility, we
associate with the vision sensor the fish's local right-handed
coordinate system 
(see Fig. 
or
Fig. ). The x-axis is along the fish's spinal
axis and the y-axis points to the fish's left.
| Xiaoyuan Tu | January 1996 |