Wasn't it William Peska who wrote:
>http://img115.exs.cx/my.php?loc=img115&image=pattern7jc.png
>
>What is the cause of the seemingly chaotic pattern?

I'm no media expert, but I guess it's something to do with the way that
POV is calculating the position of the "exit point" of the plane, which
is then used to determine the spacing of the samples. The "exit point"
is actually an infinite distance away, but POV somehow has to convert
that into some large finite value. I guess this value varies in an odd
way from pixel to pixel.

Normally that doesn't cause a problem, but with this periodic density
function small changes in the spacing of the samples can cause resonance
effects.

If you replace the "plane {y,-5" with a box of finite thickness,
something like "box {<-1000,-1000,-1000><1000,-5,1000>" the chaotic
effect goes away.

-- 
Mike Williams
Gentleman of Leisure

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