Is it like an image map? What is it really on the inside of UVPOVs little
brain? Is it 3D, is it 2D? Where does it come from? What is a photon map
exactly? (Don't worry about speaking some C, I can read it.)

Thanks in advance for your replies.

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TonyB skrev i meldingen <380b0b0f@news.povray.org>...
>Is it like an image map? What is it really on the inside of UVPOVs little
>brain? Is it 3D, is it 2D? Where does it come from? What is a photon map
>exactly? (Don't worry about speaking some C, I can read it.)
>
>Thanks in advance for your replies.
>
>

I don't know if this really belongs here, but anyway. Short Answer: You can
read the documentation of uvpov, a file called photons.htm.

Longer:
A photon map is created by shooting imaginary photons from the light source
and see how they interact with objects in the scene. Usually, povray uses
*backward* raytracing, following photons the wrong way. But them you cannot
simulate caustics or light reflecting around corners et.c. Therefore, photon
mapping shoots rays the other way, thus making an approximation of what it
might look like in the real world. Forward ray-tracing is a very
time-consuming process, and photon mapping requires a lot of memory.

Summary: Photon mapping is a hybrid of backwards and forwards raytracing,
simulating some of the light cast in the "correct" direction.

Anyone?

Simen.

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The photon map is 3D.  That's about all I remember about it.

-Mike

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TonyB wrote:

> Is it like an image map? What is it really on the inside of UVPOVs little
> brain? Is it 3D, is it 2D? Where does it come from? What is a photon map
> exactly? (Don't worry about speaking some C, I can read it.)
>
> Thanks in advance for your replies.

http://www.gk.dtu.dk/home/hwj/

earl

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TonyB <ben### [at] panamaphoenixnet> wrote...
> Is it like an image map? What is it really on the inside of UVPOVs little
> brain? Is it 3D, is it 2D? Where does it come from? What is a photon map
> exactly? (Don't worry about speaking some C, I can read it.)
>
> Thanks in advance for your replies.

Definately take a look at the link that Earl provided (or have a glance at
my paper).

Anyway, a photon map 3d.  The data is stored in a data structure called a
kd-tree (in this case, a 3d-tree).  The kd-tree is similar to a binary tree,
but each split could occur on any one of the three dimensions.  Each
forwards-ray-trace intersection is stored in the tree with intensity and
directional data.  This allows quick access to the data.

During the final rendering step, the tree is searched to find data points
that are near the current point.

-Nathan

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Nathan Kopp wrote:

> Anyway, a photon map 3d.  The data is stored in a data structure called a
> kd-tree (in this case, a 3d-tree).  The kd-tree is similar to a binary tree,
> but each split could occur on any one of the three dimensions.  Each
> forwards-ray-trace intersection is stored in the tree with intensity and
> directional data.  This allows quick access to the data.
>
> During the final rendering step, the tree is searched to find data points
> that are near the current point.
>
> -Nathan

I've been trying to search the web on information regarding this kd-tree
specifically.  Can you suggest a website that I may go to so that I can read
more.

earl

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Earl Ehrig wrote:

> I've been trying to search the web on information regarding this kd-tree
> specifically.  Can you suggest a website that I may go to so that I can read
> more.
> 
> earl

I have seen articles on using this approach in the RTNews by Eric Haines.
Try a search of his site for related material.

http://www.acm.org/tog/resources/RTNews/html/

-- 
Ken Tyler -  1100+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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