>
> hello,
>
> i have an issue using photons on one scene.
>
> i get this error :
>      "Possible Photon Error: Photon map for media is empty."
>
>
>
> excerpts from the source :
>
> #declare usePhotons = true;
> ...
> ...
> global_settings {
>      assumed_gamma 1.80
>      max_trace_level 32
>      #if (usePhotons)
>          photons {
>              #if (file_exists(photonFile))
>                  load_file photonFile
>              #else
>                   count 1000000
>                   autostop 0
>                   jitter 0.20
>              save_file photonFile
>              #end
>              }
>      #end
>      }
> ...
> ...
> light_source {
>      p2r(30, 50, 1000,false)
>      color White //Wheat // White
>      #if (usePhotons)
>         photons {
>              refraction on
>              reflection on
>              }
>      #end
>      }
> ...
> ...
>      sphere {
>          <0, rSphere, 0>, rSphere
>          translate <xIndex,0,zIndex>*2*rSphere
>          translate index*deltaY*y
>          translate index*<1,0,1>*rSphere
>          material { materialVerre }
>          #if (usePhotons)
>              photons {
>                  target
>                  refraction on
>                  reflection on
>                  collect off
>                  }
>          #end
>          }
>
>
>
> who can help me find my error ?
> thanks
>
>
> ---
> Kurtz le pirate
> Compagnie de la Banquise

I've found that this message can show when you save photons for later 
use and there is NO media in the scene. In my case, there was fog but no 
proper media.
I suspect that it can also appen if there is no media and no fog.



A little hint:
You don't need to add any photon block to your light_source unless you 
want to use photons{ area_light }.
The default photons block for all light_source, except shadowless, is:
photons{ reflection on refraction on area_light off}

Also, having a photons block when photons is not activated in the 
global_settings block don't have any effect. So, the
#if (usePhotons)...#end have no real use outside of the 
global_settings{...} block.



Alain

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