Jim McElhiney wrote:
> 
> [...]
> 
> The 1600 samples were created by a fairly sophisticated program
> (given the apparent simplicity of the problem), which I might, or might
> not, be able to find kicking around.  I spend MANY days on it.  (really!)
> Basically, it tries to meet the following criteria:
> [...]

That complies well with the observations that have been made with the
sample set, namely that it is fairly good at certain count values but
quite limited for values in between.  When you use 'normal on' in
radiosity (i think this was added by Nathan) it is not guaranteed that the
first N samples are actually used when you use 'count N'.  Another
observation i made was that the sample distribution has a 'rim' structure
at low counts (a lot of samples at the same elevation/theta values, this
could be caused by the way you solved the 'horizon problem').

The changes that will be in next Megapov concerning this are:

- alternative custom (specified in the script) or generated (halton
sequence) sample sets.  The latter is already available in MLPov:

http://martial.rameaux.free.fr/mael/mlpov083.html

- optional random rotation of the sample set around the normal vector. 
This was suggested by Michael Andrews:

Subject: Re: Radiosity flouroescent lighting troubles
Date: Thu, 28 Nov 2002 13:07:10 +0000
From: Michael Andrews <m.c### [at] readingacuk>
Newsgroups: povray.advanced-users

and works quite well in many cases.  

> 
> Note, if you have artifacts in a picture for which you want very high
> quality output, it is 99% certainty that the problem is a bug in the
> software (sorry) or the choice of other parameters, and <1% chance
> you really need more samples.

You need quite a lot of samples when you have strong local variation of
brightness i.e. small and very bright objects.  Of course it is quite
possible that there is a bug somewhere so it needs more samples to produce
smooth results than really necessary.

I tested your suggestion about ot_index and it seems to make some
difference but not much while the difference in speed can be quite
significant (more than twice the time in one test).  It could of course be
that i just tested with the wrong kind of scene and settings.

Christoph

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