> well, it is quite a while since I looked into the POV-sources, but IIRC 
> POV
> adds a build in constant value (epsilon?)  when it shoots a shadow test 
> ray to
> avoid problems with self shadowing.

Yeah, I think that's what this is. One thing I've been wondering lately is 
if it's possible to avoid doing this for objects besides the one the ray is 
coming from. So if you hit a sphere, and there's a nearby box, you do 
shadow/reflection traces *without* an epsilon, from the exact intersection 
point on the sphere. If the trace hits the box, you assume the intersection 
is valid. If the trace hits the sphere, you say "hey, this is the same 
object we're coming from," and only then do you check the epsilon and 
discard the intersection if it's too close.

You could also require that the normal of the intersection is similar to the 
normal of the original intersection; this would avoid throwing away 
intersections at an "inner corner."

 - Slime
 [ http://www.slimeland.com/ ]

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