It seems a ray traced (from the camera) through the transparent object
(entering and then exiting) and hitting a diffuse surface is treated
differently than one that hits the surface directly when considering
"radiosity".

Initially, I thought the cause had to do with media interaction, but after
commenting out the 'interior' and 'media' and 'hollow', I found the problem
still exists.  Translating the 'box' along the 'y-axis' confirms that the
problem only occurs when the primary camera ray first passes through the
box before hitting a diffuse surface.  Moving the right along the x-axis
also visualizes the problem.

Is this a known bug, or Is there a setting in the scene language that could
fix this???

* See 'povray.text.scene-files' (with subject "Radiosity and Media Bug???")
for image rendered using my version of POV-Ray v3.6, where the bounds of
the media box container is visualized.

Below is the scene file:



#include "colors.inc"

global_settings
{
    assumed_gamma 1.0
    max_trace_level 5
    noise_generator 3

#if(1)
    radiosity
    {
        media on
        count 32
        recursion_limit 3
        nearest_count 10
        error_bound 0.5
    }
#end
}

background { color White }

//----------------------------------------------
// CAMERA
//----------------------------------------------
camera {
  location <2, 4, 12>
  look_at <0,1, 0>
  up <0,1,0>
  angle 60
}

//----------------------------------------------
// Media
//----------------------------------------------
box {
    <0,0,0>, <1,1,1>
    texture {
        pigment {color rgbf 1}
    }
#if(0)
 interior {
  media {
   scattering { 1, rgb 0.2}
   intervals 1
   samples 20
   method 3
  }
 }
    hollow
#end
   scale <6,6,6>
   translate <-2,.3,0>
}

//----------------------------------------------
// GROUND
//----------------------------------------------
object {
    isosurface {
     function {y}
     contained_by {box {<-100,-3,-100>, < 100, 1, 100>}}
     texture {
            finish {
               ambient 0.0
               diffuse 1.0
               specular 0.0
            }
            pigment { color rgb <1,1,1> }
        }
    }
   hollow
}

//----------------------------------------------
//  WALL
//----------------------------------------------
box { <-2.0, -0.2, -2.0>, <2.0, 0.2, 2.0>
    finish {
       ambient 0.0
       diffuse 0.9
    }
    pigment { color rgb <1,1,1> }

    scale 5
    rotate <0, 0, -90>
    translate <-4,5,0>
}

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