Eric Freeman wrote:
> 
> Hey all,
> 
> Here's the code which causes the problem with the torus.
> ...
> camera {
> ...
>     location <0,0,-10000>
> ...
> torus {
>   1.3, 0.7
> ...


Size of distance from eye to torus ~ 10000.  After substitution into
fourth order equation, yields values ~1.0e16.  Solve for values of order
~0.01 (for a 1.3 rad torus filling 100 pixels).  Requires more than 18
digits of precision.

Double precision on standard Intel chips is ~15 decimal digits.

Result: lots of speckles in torus.

Fix: Intersect ray with bounding box of torus before solving quartic. 
Move start point of ray to point of intersection.  Speckles go away.

Workaround for current POV-Ray?  Don't know, perhaps intersect torus
with a box that is a little bigger than it to force ray origin to be
closer.

Xander

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