Warp <war### [at] tagpovrayorg> wrote:
> Eric Buddington <ebu### [at] wesleyanedu> wrote:
> > I can't quite figure how
> > (in the FAQ's example) a distance of 10^5 is enough to cause these
> > artefacts
>
>   It's not the distance alone. It's in conjunction with the really small
> camera angle. Even though alone both numbers are very accurate in 64-bit
> floating point representation, when they are combined and the results
> used for the ray-sphere intersection calculations, the inaccuracies
> start showing themselves.
>
> --
>                                                           - Warp

I am sorry to disturb
but when you replace the sphere with an isosurface, there is no problem.

Explicitly replacing

camera { location -z*1e5 look_at 0 angle .002 }
light_source { <10,20,-30>, 1 }
sphere { 0,1 pigment { rgb 1 } }

with even

camera { location -z*1e10 look_at 0 angle 0.00000002 }
//camera { location -z*1e5 look_at 0 angle .002 }
light_source { <10,20,-30>, 1 }
isosurface {
  function {sqrt(x*x + y*y + z*z) - 1}
  threshold 0 contained_by {box {<-1,-1,-1>, < 1, 1, 1>}} open
  pigment { rgb 1 }
} // end of isosurface -----------------------------------------

did not show the rendering problem from the original scene.

So how do you think this replaced scene is calculated with higher precision?

IMHO it shows that something is lets say not optimal in the current
implementation of POV-Ray. I can't say exactly what, that would require
source code analysis.

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