On Mon, 25 Jan 1999 11:24:47 -0600, Thorsten Froehlich 
	<fro### [at] charliecnsiitedu> wrote:
>In article <36ac79eb.0@news.povray.org> , par### [at] my-dejanewscom (Ron 
>Parker) wrote:
>
>> I can't think of any way to
>> detect a ray that is parallel to the bounding slab
>
>Hmm, if I understand it right the heightfield is bounded by two parallel
>planes, so all you need to test is if a ray is parallel one of the planes
>(which is easy). Then you test is there is any intersection with this ray
>and the heightfields within the first 2*sqrt(2) (for a heightfield scaled to
>1 only) and you are done.

Not necessarily.  If you're using tiled heightfields as described here,
and the tile is a high resolution and consists of all zeros except 
for a 1 in the exact center (at (.5,.5)), there are an infinite number 
of rays which will not intersect within the space of two tiles but will 
intersect at some point beyond that (consider the ray that starts at 
(0,0) and proceeds in the direction of (.5,5.5)), and there are an 
infinite number of rays that will never intersect at all (consider the 
ray that starts at (0,.5) and proceeds due northeast).

Post a reply to this message