
 Ray Tracing News, Volume 5, Number 3 
  From the vector components (dx, dy) from a test point to a polygon vertex, get an angle using arctan (or the fast approximation, in which case do not scale to radians or degrees; use the angle value in the range 0 to 8). 
  The case of a test point coincident with a polygon vertex must be explicitly checked, as the arctangent for a zerolength vector is undefined. 
  If your polygon is convex, (more generally, your polygon is starshaped,) you can preprocess the polygon into triangle strips by connecting any point in the kernel of the polygon with each vertex of the polygon. 
 www.acm.org /tog/resources/RTNews/html/rtnv5n3.html (3923 words) 
