Subtracting two isosurfaces to create a shell, portions of the shell where the
inner (subtracted) surface should be visible are completely transparent.  Some
shadows are cast by the invisible shell.  Other shapes I've tried do not do
this.

I've tried this on Linux (Kubuntu 9.10 fully patched, POV-ray 3.6.1 as compiled
by Debian) and Windows Vista (32-bit fully patched, POV-ray 3.6.2 and
3.7.beta.35a) on a P4 dual core 3GHz, 3GB RAM computer, and on WinXP Home
(POV-ray 3.6.2 and 3.7.beta.35a, Core 2 Duo 2.33GHz, 1GB RAM, Japanese).

Sample code:


background { color <0,0.1,0.2> }

camera {
  orthographic
  location <2, 6, -20>
  right <8, 0, 0>
  up <0, 6, 0>
  look_at <0, 0, 0>
}

light_source { <50, 50, -20> colour <1,1,1> }
light_source { <-20, -5, -10> colour <1,1,1> }
light_source { <-2, 5, -10> colour <1,1,1> }

difference{
isosurface{
    function{ pow(x,2) + pow(y,2) + pow(z,2) - pow(2.5,2) }
    contained_by { sphere { <0,0,0>, 2.51 } }
    max_gradient 5.1
    pigment{color <1,1,0>}
           }
isosurface{
    function{ pow(x,2) + pow(y,2) + pow(z,2) - pow(2.4,2) }
    contained_by { sphere { <0,0,0>, 2.51 } }
    max_gradient 5.1
    pigment{color <1,1,0>}
           }
  box { <0, -5, 0>, <5, 5, -5>
    rotate <0, 45, 0>
    pigment{ color <1,1,0> }
       }
}

// I found the following helpful in demonstrating the issue

difference{
 torus{ 1, 0.2
      pigment{ color <1,0,0> }
      translate <0,-2.35,0>
       }
  box { <0, -5, 0>, <5, 5, -5>
    rotate <0, 45, 0>
    pigment{ color <1,0,0> }
       }
}

Post a reply to this message

On 05.03.10 06:55, F. Hydrant wrote:
> Subtracting two isosurfaces to create a shell, portions of the shell where the
> inner (subtracted) surface should be visible are completely transparent.  Some
> shadows are cast by the invisible shell.  Other shapes I've tried do not do
> this.

You need to use all_intersections if you want to use isosurfaces like this 
in CSG. This is explained in the document section about isosurfaces, see 
<http://www.povray.org/documentation/view/3.6.1/300/>.

	Thorsten, POV-Team

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Thanks!

Well, that's somewhat embarrassing.  I skimmed over that option because I'm
thinking in terms of objects rather than rays, and didn't see a problem with the
intersections of objects.

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"F. Hydrant" <dpe### [at] scphyskyoto-uacjp> wrote:
> Subtracting two isosurfaces to create a shell, portions of the shell where the
> inner (subtracted) surface should be visible are completely transparent.  Some
> shadows are cast by the invisible shell.  Other shapes I've tried do not do
> this.
>
> I've tried this on Linux (Kubuntu 9.10 fully patched, POV-ray 3.6.1 as compiled
> by Debian) and Windows Vista (32-bit fully patched, POV-ray 3.6.2 and
> 3.7.beta.35a) on a P4 dual core 3GHz, 3GB RAM computer, and on WinXP Home
> (POV-ray 3.6.2 and 3.7.beta.35a, Core 2 Duo 2.33GHz, 1GB RAM, Japanese).
>
> Sample code:
>
>
> background { color <0,0.1,0.2> }
>
> camera {
>   orthographic
>   location <2, 6, -20>
>   right <8, 0, 0>
>   up <0, 6, 0>
>   look_at <0, 0, 0>
> }
>
> light_source { <50, 50, -20> colour <1,1,1> }
> light_source { <-20, -5, -10> colour <1,1,1> }
> light_source { <-2, 5, -10> colour <1,1,1> }
>
> difference{
> isosurface{
>     function{ pow(x,2) + pow(y,2) + pow(z,2) - pow(2.5,2) }
>     contained_by { sphere { <0,0,0>, 2.51 } }
>     max_gradient 5.1
>     pigment{color <1,1,0>}
>            }
> isosurface{
>     function{ pow(x,2) + pow(y,2) + pow(z,2) - pow(2.4,2) }
>     contained_by { sphere { <0,0,0>, 2.51 } }
>     max_gradient 5.1
>     pigment{color <1,1,0>}
>            }
>   box { <0, -5, 0>, <5, 5, -5>
>     rotate <0, 45, 0>
>     pigment{ color <1,1,0> }
>        }
> }
>
> // I found the following helpful in demonstrating the issue
>
> difference{
>  torus{ 1, 0.2
>       pigment{ color <1,0,0> }
>       translate <0,-2.35,0>
>        }
>   box { <0, -5, 0>, <5, 5, -5>
>     rotate <0, 45, 0>
>     pigment{ color <1,0,0> }
>        }
> }

tanx...
its amazing information

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