Christian Froeschlin <chr### [at] chrfrde> wrote:
> To clarify, the links are not about evenly spaced points
> on a sphere, but about creating points for a light dome.

I haven't checked out those links, but I've got a good way to produce an
arbitrary number of evenly-spaced points on a sphere. It's based on the Fermat
Spiral, but adapted to work on a sphere (can't remember where I found it):

union{
 #local NPoints = 256;
 #local Radius  = 1;

 #local Inc = pi * (3 - sqrt(5));
 #local Off = 2 / NPoints;
 #for(K, 0, NPoints-1)
  #local Y = K * Off - 1 + (Off / 2);
  #local R = sqrt(1 - Y*Y);
  #local Phi = K * Inc;

  #local ThisPoint = <cos(Phi)*R, Y, sin(Phi)*R>*Radius;
  sphere{ThisPoint, .1}
 #end

 pigment{rgb 1}
}

"And" <49341109@ntnu.edu.tw> wrote:
> It seems useful and have many information.
> Previously, I found that Samuel Benge's macro seems easy to use, so I asked for
> this directly.
> Thank you.

My geodesic sphere code is not the best choice, as it produces duplicate points,
and you can't just /choose/ any number of points you want (when dealing with a
light dome made up of numerous light_sources, you would probably want an easy
way to fine-tune quality over speed). The above code should work fairly well for
producing an array of lights for a light dome.

Maybe somebody who has experience working with light domes can put it to use.

Sam

Post a reply to this message

> Christian Froeschlin <chr### [at] chrfrde> wrote:
>> And wrote:
>>
>>> Could I ask for a macro that creats position points on sphere in an array? Or it
>>> has existed?
>>
>> Try
>>
>>
http://news.povray.org/povray.binaries.images/thread/%3C461ba1e1%40news.povray.org%3E/?mtop=241021
>>
>> and
>>
>>
http://news.povray.org/povray.binaries.scene-files/thread/%3C461efe8a%241%40news.povray.org%3E/
>>
>> These are from 2007 so the code probably needs to be adapted for 3.7.
>
>
> It seems useful and have many information.
> Previously, I found that Samuel Benge's macro seems easy to use, so I asked for
> this directly.
> Thank you.
>

Both of those used an now obsolete version of megapov. Megapov is a test 
bed branch of POV-Ray.

You can now use high dynamic range images directly when using the 
version 3.7. It also provide illumination when combined with radiosity.

You can also do a search for "light dome". It's a way to generate lights 
according to a high dynamic range image. The lights placement and 
density generated is not uniform as it depends on the bright parts of 
the source image.



Alain

Post a reply to this message

"Samuel Benge" <stb### [at] hotmailcom> wrote:
> I haven't checked out those links, but I've got a good way to produce an
> arbitrary number of evenly-spaced points on a sphere. It's based on the Fermat
> Spiral, but adapted to work on a sphere (can't remember where I found it):
>
> union{
>  #local NPoints = 256;
>  #local Radius  = 1;
>
>  #local Inc = pi * (3 - sqrt(5));
>  #local Off = 2 / NPoints;
>  #for(K, 0, NPoints-1)
>   #local Y = K * Off - 1 + (Off / 2);
>   #local R = sqrt(1 - Y*Y);
>   #local Phi = K * Inc;
>
>   #local ThisPoint = <cos(Phi)*R, Y, sin(Phi)*R>*Radius;
>   sphere{ThisPoint, .1}
>  #end
>
>  pigment{rgb 1}
> }
>
> My geodesic sphere code is not the best choice, as it produces duplicate points,
> and you can't just /choose/ any number of points you want (when dealing with a
> light dome made up of numerous light_sources, you would probably want an easy
> way to fine-tune quality over speed). The above code should work fairly well for
> producing an array of lights for a light dome.
>
> Maybe somebody who has experience working with light domes can put it to use.
>
> Sam

Oh, you are kind. Thanks.
Although I have no experience with light dome, I intend to make one.
I will try it.


Alain <kua### [at] videotronca> wrote:
>
> Both of those used an now obsolete version of megapov. Megapov is a test
> bed branch of POV-Ray.
>
> You can now use high dynamic range images directly when using the
> version 3.7. It also provide illumination when combined with radiosity.
>
> You can also do a search for "light dome". It's a way to generate lights
> according to a high dynamic range image.
>


I'm unfamiliar with megapov except for viewing its mechanical simulation several
years ago, I know that pov-ray 3.7 can use hdr image directly. However those
links contain the theme you just mentioned such as lights placement depends on
the brightness of the point.
It is a bit hard to me, and with my poor english it is harder when I read them.

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