
 Combinatorial Solid Geometry, Boundary Representations, and NonManifold Geometry 
  Ray behaviors such as perspective, reflection, refraction, etc, are entirely determined by the applications program logic, and not by the raytracing library. 
  For example, the geometry information associated with a planar face is the plane equation which includes the outwardpointing surface normal; the plane equation does not have to be rederived from the vertices. 
  If the ray hits an edge of a loop in a face, and there is another loop of the face of the same type (interior/exterior) adjacent on the edge, the hit is registered as if the ray had intersected the interior of the loop. 
 ftp.arl.mil /~mike/papers/90nmg/joined.html (20066 words) 
