Thank you for expanding so much effort to educate me, and I apologize for
introducing the confusion with the mirror shape.

While playing with the scene you generously provided, I found it helpful to
decrease the intensity of the light source in order to get a better
understanding of the central white spot one gets when using the light source
of intensity close to 1.

Thanks again,

Goran


"hughes, b." <omn### [at] charternet> wrote in message
news:3dca028d@news.povray.org...
> I just can't win when I'm doing this stuff immediately to help people.
> Hopefully I'm not to late to say that the #switch directive was left out
> before.
>
> Oh well, gives me a chance to post this new scene file which writes and
> reads the results.
>
>
> /* how to test flashlight beam on wall for brightness */
>
>
> /* use appropriate command for each rendering or you'll overwrite the
image
> */
>
> // create scene
> // cmd:+fn +oC:\images\flashlite.png
>
> // write file
> // cmd:-f
>
> // read file
> // cmd:-f
>
>
> // which scene? 1 or 2, any other number to read file
> #declare Scene=0;
>
> #switch (Scene)
> #case(1)
> /* setup scene */
> global_settings {
>  photons {
>   spacing 0.02
>   // autostop 0
>  }
> }
>
> camera {
> location <0, 0, 0>
> look_at <0, 0, 1>
> }
>
> // I used a different paraboloid here
> quadric {
> <0.5, 0.5, 0>, <0, 0, 0>, <0, 0, -1>, 0
> clipped_by {
>  plane {z,2} // wide end opening
>  plane {-z,-0.2} // narrow end opening
>  }
> texture {
>  pigment {rgb 0.5}
>  // a little imperfection for realism
>   normal {dents 0.05 turbulence <0.2,0.2,0.4> scale <0.3,0.3,0.9>}
>   // surface finish
> finish { ambient 0 diffuse 0 specular 0.99 roughness 0.003
>  reflection {0.95}
>  }
> }
>  photons {
>   target
>   reflection on
>   refraction off
>    collect off
>   }
> }
>
> // Define a plane on which to measure the light
> plane { z, 7.0
> pigment { color blue 1 }
> finish {
>  // specular highlights, other finish characteristics might be important
>   ambient 0.1 diffuse 0.2 specular 0.1 roughness 0.09
>   }
>  photons {
>   target
>   reflection off
>   refraction off
>    collect on
>   }
> }
>
> // Define a light source
> light_source { <0, 0, 1>, <0.7, 0.8, 0.9>
>  fade_distance 3
>  fade_power 1
>  photons {
>   reflection on
>   refraction off
>   }
> }
>
> #break
> #case (2)
> /* testing scene */
>
> // Find light intensity (pigment of plane)
>
> #include "functions.inc"
>
> #declare Image=
>  pigment {
>   image_map {
>    png "flashlite.png"
>    once
>   }
>    translate -0.5
>    scale <4/3,1,1>
>  }
>
> plane {z,1
>  pigment {Image}
>  finish {ambient 1 diffuse 0}
> }
>
> camera {
>  orthographic
>  location 0
>  look_at z
>  right 4/3*z
>  up y
> }
>
>
> #declare I=0.1; // increment
>
> #fopen FlashLight "c:\\images\\flashlight.txt" append
>
> #declare X=-4/3/2;
>
> #while (X<=+4/3/2)
>
> #declare Y=-1/2;
>
> #while (Y<=+1/2)
>
> #declare Point=<X,Y,0>;
>
> #declare Intensity = eval_pigment(Image, <Point.x, Point.y, Point.z>);
>
>  #write (FlashLight
>   concat(
>  str(Point.x,1,-1),
>  ",",
>  str(Point.y,1,-1),
>  ",",
>  str(Intensity.gray,1,-1),
>  ",\n" // last comma so data can be read later
>  )
>  )
>
> #declare Y=Y+I;
>
> #end
>
> #declare X=X+I;
>
> #end
>
> #fclose FlashLight
>
> #break
>
> #else // if not 1 or 2
>
>
> /* Scene!=1|2 */
>
> #fopen FlashLight "c:\\images\\flashlight.txt" read
>
>  #while (defined (FlashLight))
>
>  #read (FlashLight, Px, Py, Il)
>
>  #debug concat(str(Il,1,-1),"\n") // anything else could be done here
>
>  #end
>
> #end // switch
>
>

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