Re: [Algorithms] fast triangle-segment test *with precomputation*

[<SHA...@ao...>]

In a message dated 07/08/00 17:36:44 !!!First Boot!!!, 
al...@ex... writes:

<< A few questions about your 3rd test:
 - Are you testing line or line segment intersection?
 - Why do you need to use the diagonal?
 - Doesnt the test hold for any bbox edge as well.
 - Also why are you testing 8 lines?  Four parrallel
   bbox edges should be enough to cover any case where
   a corner 'punches through the triangle'
 
 Alex >>

This third test is done because of the possibility of a triangle location 
which has 

1) No vertices inside the box
2) No edges which intersect any box face

In this case I compute 4 ( you are right, I overestimated when I tried to 
visualise this! :) ) line segments and test if these intersect the face of 
the triangle.

Having just looked at your reply you are also right in that 4 parallel box 
edges would do exactly the same thing as 4 diagonal lines.

My bbox structure does not actually contain edges, only 2 3d points which are 
enough to describe a square cube so for me it is just a matter of choice 
whether to use parallel or diagonal edges/lines.

Regards,

John.