Rune Winsevik wrote:
> 
> Hi Pov People!
> 
> I've run into this problem: When we're modelling a tranparent object
> and place it on another surface (a floor, a table etc.) we get an ugly
> effect. The bottom surface of the transparent object will have the
> same y-value as the surface that the object is placed on. Is this
> something POV don't like? As an example I've included a minimalistic
> POV file with a "floor" and a simple transparent object. As you'll see
> the bottom surface of the transparent object goes ape (since it lies
> in the same plane as the "floor"?). Can someone explain to me why this
> happens?
> 
> Thanks!
> 
> -Rune
> 
> The .pov file:
> ========
> 
> global_settings
> {
>    assumed_gamma 2.2
>    ambient_light 0.8
> }
> 
> background { color rgb <0.9, 0.9, 0.9> }
> 
> camera
> {
>    location <100, 100, 100>
>    angle 18
>    look_at  <0,5,0>
> }
> 
> light_source { <250, 200, -100> color 1.5 }
> 
> // Floor
> #declare T1 = texture
> {
>   pigment { rgb <.5, .5, .9> }
>   finish { ambient 0.70 diffuse 0.70 }
> }
> mesh
> {
>   smooth_triangle
>   {
>     <-500, 0,  500>, <0,1,0>
>     < 500, 0,  500>, <0,1,0>
>     <   0, 0, -500>, <0,1,0>
>   }
>   texture {T1}
> }
> 
> // Transparent object
> #declare T2 = texture
> {
>   pigment { rgbt <.6, .6, .6, 0.90> }
>   finish { ambient 0.5 diffuse 1.0 }
> }
> mesh
> {
>   smooth_triangle
>   {
>     <-10, 0,   5> <0, -1, 0>
>     <  0, 0, -10> <0, -1, 0>
>     < 10, 0,   5> <0, -1, 0>
>   }
>   smooth_triangle
>   {
>     <-10,  0,   5> <0, .6, .8>
>     < 10,  0,   5> <0, .6, .8>
>     <  0, 20,   0> <0, .6, .8>
>   }
>   smooth_triangle
>   {
>     < 10,  0,   5> <0.4,0.82,-0.4>
>     <  0,  0, -10> <0.4,0.82,-0.4>
>     <  0, 20,   0> <0.4,0.82,-0.4>
>   }
>   smooth_triangle
>   {
>     <  0,  0, -10> <-0.4,0.82,-0.4>
>     <-10,  0,   5> <-0.4,0.82,-0.4>
>     <  0, 20,   0> <-0.4,0.82,-0.4>
>   }
>  texture {T2}
> }
> 
> --
> --------------------------------------------------------------------
> Remove "SPAM?NO!" to reply. My home is at: http://home.sol.no/~runew
> 
The problem your encountering is called coincidental surfaces you can
read about in the povray docs.

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