I could reproduce it. I have once had the same effect in a
scene of mine. Yet, I was able to get rid of it by playing
around with (read: cranking up) the antialias options inside
the media.

So I guess this is not a bug, but rather an alias problem.

Markus

Rob Boxman wrote:
> 
> When rendering the following scene, POV-Ray 3.1 shows some unrendered black
> circles at the opposite direction of the spotlicht beams in the media.
> Is this something known, and is there a workaround for this?
> 
> This scene is an altered version of the media2.pov example file:
> 
> // Persistence Of Vision raytracer version 3.1 sample file.
> //
> // Participating media with spotlights.
> //
> 
> //
> // The camera.
> //
> 
> camera {
>   location <0.5, 5, -10>
>   right 4/3*x
>   up y
>   direction z
>   angle 65
>   look_at <0, 5, 0>
> }
> 
> //
> // Add media.
> //
> 
> media {
>   intervals 10
>   scattering {1, rgb 0.02}
>   samples 1, 10
>   confidence 0.9999
>   variance 1/1000
>   ratio 0.9
> }
> 
> //
> // Spotlights pointing at shaft.
> //
> 
> #declare Spot = light_source {
>   <0, 0, 0> color rgb<1, 1, 1> * 3
>   spotlight
>   point_at <0, -1, 0>
>   radius 2
>   falloff 4
>   media_attenuation on
> }
> 
> #declare Spots = union {
>   object { Spot }
>   object { Spot rotate <0, 0, 10> rotate <0,   0, 0> }
> //  object { Spot rotate <0, 0, 10> rotate <0,  30, 0> }
>   object { Spot rotate <0, 0, 10> rotate <0,  60, 0> }
> //  object { Spot rotate <0, 0, 10> rotate <0,  90, 0> }
>   object { Spot rotate <0, 0, 10> rotate <0, 120, 0> }
> //  object { Spot rotate <0, 0, 10> rotate <0, 150, 0> }
>   object { Spot rotate <0, 0, 10> rotate <0, 180, 0> }
> //  object { Spot rotate <0, 0, 10> rotate <0, 210, 0> }
>   object { Spot rotate <0, 0, 10> rotate <0, 240, 0> }
> //  object { Spot rotate <0, 0, 10> rotate <0, 270, 0> }
>   object { Spot rotate <0, 0, 10> rotate <0, 300, 0> }
> //  object { Spot rotate <0, 0, 10> rotate <0, 330, 0> }
> }
> 
> object {
>   Spots
>   rotate <90, 0, 0>
>   translate <0, 5, 0>
> }

-- 
Dipl.-Ing. Markus Becker

Siegen, Germany

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