"Greg M. Johnson" <"gregj;-)56590\""@aol.c;-)om> wrote in message
news:3b89ae44@news.povray.org...
> Can someone explain to me why I get a "thick-walled tube" with the
> following code?
>
>
> #declare actuald=2;//d*0.125;
>
> #declare scopey=
> union{
>         difference{
>                 cylinder {<0,0,-0>,<0,0,3>,actuald+.000000100}
>                 cylinder {<0,0,-.1>,<0,0,3.1>,actuald}
>                 pigment{Brown} finish {ambient 0.8}
>                 }
>         }
>
> object {scopey rotate <0,0,0>}
>
> camera {
>    location <0, 0, -15> file://was z of 15
>        angle 22
>    look_at <0,0,60>
> }
>
>
> light_source { <80, 1620, 80> color White }
> light_source { <-4000, -400, -4000> color White*.6 }
>
>

Try the following:

#declare actuald=2;//d*0.125;

#declare scopey=
union{
 difference{
  cylinder {<0,0,-0>,<0,0,3>,actuald+.000000100}
  cylinder {<0,0,-.1>,<0,0,3.1>,actuald}
  pigment{
   gradient z
   color_map {
    [0 color rgb 0]
    [1 color rgb 1]
   }
   scale <1,1,3>
  }
  finish {ambient 1}
 }
}

object {scopey rotate <0,0,0>}

camera {
 location <0, 0, -15> file://was z of 15
 angle 22
 look_at <0,0,0>
}

Basically, the tube itself is very thin walled, but the far end of the tube
is much smaller (on the screen) than the near end.  Because of this, you get
the illusion of a thick wall.  Really, you're just looking inside the tube.
The gradient pattern above should highlight this.

...Chambers

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