On 28-2-2019 19:25, MichaelJF wrote:
> I commented the steam fog approximation out, so it rendered a little bit 
> faster. One sees two instances of the same object (it is the example 
> from the tutorials shipped with POV but in a box {-2,2 } instead of a 
> sphere). The only difference is
> 
> object { Sonne
>     scale <500,500,500>*5
>     translate MediaPos
> }
> 
> object { Sonne
>     translate <3,1,5>
> }
> 
> with MediaPos=< 649.685959 , 1442.616855 , 39968.697311 >
> 
> Obviously I will not use it in my scene. It's just a riddle I 
> encountered by chance. I played a little bit with intervals, samples, 
> variance, confidence but without any success. It seems to be due to the 
> scaling alone.
> 

My immediate reaction to this would be: "Did you take the scaling into 
account in the media build of Sonne?"

You need to do the following /essential/ operation, for the first 
instance, concerning the emission and, if applicable, scattering and 
absorption:

#local MediaScale = <500, 500, 500>*5;

sphere {<0,0,0>, 1 //or a box of course
   hollow
   pigment {rgbt 1}
   interior {
     media {
       samples 50
       emission <0.8, 0.8, 0.8>/MediaScale
       scattering {1, rgb <0.1, 0.1, 0.1>/MediaScale}	
       density {
	spherical
	density_map {
	  [0.20 rgb 0.0]
	  [1.00 rgb 1.0]
	}
       }
     }
   }
   scale MediaScale
}

This is explained in the docs btw in 2.3.7.5 Media and transformations.

I think that lies at the root of your problem.

-- 
Thomas

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