Mike nous illumina en ce 2009-01-14 16:50 -->
> I have been trying to model an experiment with two different liquids with
> different indicies of refraction with one on top of the other.  With help from
> this forum I am nearly able to get it modeled nicely.  However, It still does
> not look correct when looking from a perspective view.  I have made a very
> simple approximation.  Two objects with different refractive indices on top of
> each other. Looking at it from a perspective view has some weird artifacts and
> does not look correct.  I have been scratching my head for a while on this one.
>  I tried merging, shifting up and down, etc.  I have posted my code below,
> please take a look.
> 
> Thanks,
> Mike
> 
> #include "colors.inc"
> #include "textures.inc"
> 
> global_settings{max_trace_level 255}
> camera {
>      location  <0, 3, 160>
>     look_at   <0, 3, 0>
>     angle 2.5
>       rotate <-30*1,-30*1,0>
>    }
> #declare MaterialAlcohol =
> material {
>   texture {
>      pigment {
>         color rgbf<1, 1, 1,1>
>       }
>  finish {
>         ambient 0.0
>         diffuse 0.0
>          reflection {
>           0.0, 1.0
>           fresnel on
>         }
>         conserve_energy
>         specular  0
>         roughness 0
>  }
>   }
>   }
> 
>   #declare HeavyLiquid =
> material {
>   texture {
>      pigment {
>         color rgbf<0.6, 0.5, 0,1>
>       }
>  finish {
>         ambient 0.0
>         diffuse 0.0
>          reflection {
>           0.0, 1.0
>           fresnel on
>         }
>       conserve_energy
>        specular 0
>      roughness 0
>  }
>   }
>   }
> 
> 
> #declare AlcoholRegion=
> box { <-1.899, 0.2, -1.899>, <1.899, 3, 1.899>
> material { MaterialAlcohol }
>   interior {
>   ior 1.3800
> }
>  }
> 
> #declare HeavyLiquidRegion=
> box { <-1.899, 3, -1.899>, <1.899, 5, 1.899>
> material { HeavyLiquid }
>  interior {
>     ior 1.4
> }
> }
> 
> //merge{
> object{AlcoholRegion}
> object{HeavyLiquidRegion}
> //}
> light_source {
>     <4, 8, 10>
>     color White
>   }
> plane{y,0 texture{pigment{White}finish{ambient 0 diffuse 1}}}
> 
> 
> 
The two objects with the different ior have a coincident surface. That's 2 faces 
that are exactly at the same location. When a ray reatch those, it can't readily 
chose between whitch one is encountered first. Then, you have rounding errors 
from the FP number crunching.

The cure is to move one object a very little bit.
The best way may be to have the two objects overlap by a small value:
change "HeavyLiquidRegion" dimentions as follow
box { <-1.899, 2.9999, -1.899>, <1.899, 5, 1.899>

OR, you can do it the other way and create a small gap:
box { <-1.899, 3.0001, -1.899>, <1.899, 5, 1.899>

-- 
Alain
-------------------------------------------------
There will always be beer cans rolling on the floor of your car when the boss 
asks for a ride home from the office.

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