On Wed, 03 Feb 1999 10:38:47 -0500, Nathan Kopp <Nat### [at] Koppcom> wrote:

>That is a very interesting idea!  Have you done any testing on it yet?  I'm
>interested in how well it performs.  Are you considering adding it to POV
>eventually?  If so, we should (at some future time) discuss how photon maps
>and the contributing network can work together (unless, of course, the
>contributing network works so well that it replaces the photon maps... I
>won't feel too bad if that happens).
>

I'm an old DOS programmer, admittedly.   POV is a Win95 app.  I'm not very
confident when programming windows apps.  For one thing, I'm not sure about
how to use POV_Alloc().  I need to get the amount of free extended memory too.
This would mean more than just writing the code. I need to learn the details
of Win-Apps.  And I also need to become comfortable with Borland 5.0, meaning,
a book on it would be nice.  This is why patches written by me aren't
springing up in binaries.programming


>Steve wrote:
>> 
>> Tell me what you mean by random sampling. What are you sampling exactly?
>> Thanks.
>
>I was speaking of the beams shot out of the light source into the scene.
>Originally, I chose a random theta/phi combination (based on a good PDF
>which was supposed to lead to uniform distribution over the area of the
>unit sphere).  But I was also speaking of splitting those beams up when
>they hit a diffuse surface.  Sample beams would then be chosen over the
>unit hemisphere based on the surface normal.  This time, the PDF favored
>rays based on the surface's BRDF.
>

I see.  It sounds like you are taking an entirely random distribution of rays
and focusing them in peaks of the BRDF of a given point.  So you want to shoot
more rays where there are high emmisions in the BRDF.  This is initially a
good idea, and I can see why noise would result.    Try an even distribution,
and let the natural light level of the rays do the dirty work.  You will get a
smaller number of "important" rays, though.   The question is: is this a bad
thing?   

For very tight BRDFs, use cut-off angles, wherein you dont shoot any rays
outside the bright, central "cone."  This would give you an artificial way to
get more important rays emitted into the scene, without resorting to a
randomizer.  

I hear some BRDFS are a simultaneous combination of a large specular peak with
a small  PDF in all directions.  Perhaps seperating the two while distributing
is a good idea?

-------------
Steve

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