Since a full visibility check for a cylinder would be computationally
expensive, we perform the following simple test: Let P be the point
on the axis of cylinder C that is closest in height to the
cyclopean origin O. Then we say that C is visible if 
, where r is the radius of C. Since the cylinders in a
typical virtual marine world in our animation are fairly scattered,
the occlusion test is neglected.
| Xiaoyuan Tu | January 1996 |