Nathan Kopp wrote:
> 
> Does that really look like your every-day probability distribution funciton
> to you?  To me it looks like the points are much more evenly spaced than any
> distribution funciton I've ever seen.  Notice how at samples=50, the samples
> are in almost perfect rings, almost like a geodesic dome.  The points are
> also considerably more evenly spaced than in the Halton sequence, which
> itself is intended to be low-discrepancy.
> 
> Also, as far as I know, we don't have the source code that generated the
> existing 1600 samples.  The file "rad_data.cpp" containing the data is
> credited to Jim McElhiney.
> 

As discussed in the thread:

Subject: Radiosity flouroescent lighting troubles
Date: Tue, 19 Nov 2002 18:43:42 EST
From: "Rohan Bernett" <rox### [at] yahoocom>
Newsgroups: povray.advanced-users

it seems to be generated by projecting a distribution on a disc onto the
hemisphere.  I have made first tests with using Sim-POV to generate a
better distribution, some first results:

http://www.schunter.etc.tu-bs.de/~chris/files/samples_internal.png
http://www.schunter.etc.tu-bs.de/~chris/files/samples_simpov.png

Note that the new distribution has slightly more samples (1850) and i did
not test how well it follows the cosine theta distribution.  

Another thing i have been thinking of is if it would not be better to have
a uniform distribution but weight the sample rays according to cosine
theta.  At least it could be worth trying if that diminishes radiosity
artefacts in some situations.  Although it seems logical that you need
less samples where the samples have not much importance the density
approaching zero at the bottom rim of the hemisphere leads to an extremely
nonuniform distribution along the rim.  

Christoph

-- 
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