I've created a test image with UVPOV using Photon Mapping. It is an
illustration of a standard class-room experiment showing refraction and
reflection. I wanted to see whether Photon mapping actually could do this,
and the results were quite surprising.

The only problem is that the rays are a bit splotchy and I cannot find good
settings for them.

It was amazing to see that the photons are refracted through the prism and
reflected on the inside, creating a zig-zag pattern as one would expect from
the real world. Rendering time was about 8 mins; 6 mins mapping photons. :/

But I am not quite happy yet. There seems to be some strange phenomena, for
example the forst refracted the stripe suddenly ends!

Any comments welcome!

Simen.

------

// beginnig of source for prism1.jpg

#include "colors.inc"

// settings for photon gathering; as in example in the docs. Lower
// phd gives better results and longer tracing time.

#declare phd=0.35;
global_settings{  
        photons{    
                gather 20, 100
                radius 0.1*phd, 2, 0.1*phd    
                //autostop 0    
                jitter .01
                expand_thresholds 0.2, 40  
        }
        max_trace_level 20
}


// an ambient light source
light_source { <-50, 50, -50> color White*0.45 }

// camera - placed on the z-axis then rotated
camera {
        location -z*30
        direction z
        up y
        right 4/3*x
        angle 40
        look_at 0
        
        rotate <47, 30, 0>
}


// some settings:
#declare w = 0.41; // witdh of constraining container
#declare l = 30; // length of containter - bigger gives narrower spreading angle on
the ray
#declare stre = 10; // strenth of light - do not increase this if l is increased -
automatic adjustment here
#declare h = 10; // height of container. Just a formality

union {
        light_source {
                <0, 2, 0> color White*l*stre
        }
        
        
                difference {
                      
  box { <-(w/2+0.5), 0, -(w/2+0.5)>, <l,  h+1, w/2+0.5> }
                        box { <-(w/2),    -1, -(w/2)>,     <l+1, h+2,
w/2> }
                        pigment {
                                color Green
                        }
                }
        translate x*-l
        rotate y*70
        translate <-7, 0, 15>

}


// the prism

box {
        -1, 1
        scale <5, 1, 3>
        translate y*1
        pigment {
                color rgbf <1, 1, 1, 0.78>
        }
        finish {
                phong 1
                phong_size 150
                reflection 0.22
                ambient 0.4
                diffuse 0.6
        }
        interior {
                ior 1.44
        }
        photons {
                separation 0.02*phd
                refraction on
                reflection on
                //ignore_photons
  }
}




// graph paper
plane {
        y, 0
        texture {
                pigment {
                        gradient x
                        color_map {
                                [0.0, 0.021 color Blue color Blue]
                                [0.021, 1.0 color White color White]
                        }
                }
        }

        texture {
                pigment {
                        gradient z
                        color_map {
                                [0.0, 0.021 color Blue color Blue]
                                [0.021, 1.0 color Clear color Clear]
                        }
                }


                finish {
                        ambient 0.01
                        diffuse 0.99
                }
        }

}

// end of source.

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