From: giovanni.piredda@hotmail.it   
      
   Hi to all,   
   I have a quite general question on algorithms for ray-surface   
   intersections: which one is the best? (here I am joking a little bit).   
      
   Let me give a few lines of context. I have played a little bit with   
   Goptical, trying out light concentration with a compound parabolic   
   concentrator, and the program misses many of the interceptions. Looking   
   in the source code, I see that for a generic surface Newton's method of   
   root finding is implemented (if I understood correctly: I was not able   
   to follow all of the details of the code).   
      
   I would like to experiment a bit with other intersection finding methods   
   - I have seen browsing the internet (e.g. the documentation for Optica,   
   the optical design program based on Mathematica and various papers on   
   ray tracing) and old postings on sci.optics as well that one can first   
   approximate the surface wih other surfaces with analytic intersections,   
   then use these as starting points for iterative algorithms.   
      
   What are good references for this problem? Books, review papers,   
   research papers?   
      
   Thanks in advance for any hint!   
      
   Giovanni   
      
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