On 9/25/19 1:38 PM, Norbert Kern wrote:
> Recently I looked at old IRTC files - again.
> 
> One of my old favorites is "Verres1" made by Herve Martin back in 1997 for the
> "Glass" IRTC round  http://oz.irtc.org/ftp/pub/stills/1997-02-28/verres1.jpg .
> 
> I translated the given source from Luxart 2.0 to Pov-Ray 3.7, which wasn't that
> difficult.
> But when adding photons, I got a far from perfect image.
> 
> Since the settings generate a 16 GB photon file, reducing spacing isn't an
> option.
> Is there a way to get rid of the blotchy artifacts?
> 
> I included the source -
>
http://news.povray.org/povray.binaries.scene-files/thread/%3Cweb.5d8ba2e7aa028214839d843b0%40news.povray.org%3E/
> 
> Regards,
> Norbert Kern
> 
I'll not be able to reasonably play with this scene on my little 
machine, but...

1) If you ran v3.7-stable, there are some photon fixes in the current 
v3.8 master branch.

2) There are dozens of solver related fixes in my v3.8 master based 
branch at:

https://github.com/wfpokorny/povray/tree/fix/polynomialsolverAccuracy

which likely help some - but you'll need to build a custom version. 
Secondary rays are more sensitive to solver accuracy issues. Your light 
sources are relatively close to the objects so you are probably not 
seeing the worst issues discussed at some length toward the bottom of 
github issue:

https://github.com/POV-Ray/povray/pull/358

and exposed by shooting photons from afar.

3) I see polygon objects in the puz2 union. These won't have a well 
defined inside / interior. I'm unsure what happens when an interior is 
later defined for a collection of shapes including those. Maybe as a 
union and not a merge it can kinda work? The sor objects are also open 
so though those have defined interiors possible in some cases where 
photon rays see the tops or bottoms photon directions won't quite be 
right. Doubt this the reason for graininess though.

4) The size of some of the shapes in puz2 especially a bit small so 
might be seeing some lost intersections. Scale scene up - a little (not 
too much - see (2) pull #358 comments for why) ?

5) I've seen odd results where the light intensities are >1 with 
photons, but never had time to run down what is going on - suspect maybe 
the gather mechanism making bad choices / bad radius choices, but 
guessing. You've got this >1 intensity set up, but no idea if your 
tripping the same issue(s).

Otherwise, not sure. If you do play with any of the options above beware 
it might be you end up suddenly with many more photons deposited at your 
current spacing.

Aside: I've never played much with stored photon files. How many 
deposited photons do you have with/in that 16GB photon file?

Bill P.

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