Gilles Tran wrote:
> 
> To be fair, POV-Ray default radiosity usually tend to work wonders and when
> the scenes are messy enough, once can get away with very low quality values.
> It's only in a few cases like this is that the radiosity problem seems
> harder to solve for POV-Ray.

We should be fair and note that we probably have hundred times more 
experience to set up radiosity in POV than you have in C4D. :-)

I have tried two more renders: the first to get an idea of how the 
'correct' solution would look like: count 1600, e-b. 0.1:

http://www.tu-bs.de/~y0013390/files/rad_01z1.png

And the following uses the 'e'-Settings previously mentioned with the 
following changes:

- always_sample is on
- count is 600
- the sample direction set is randomly rotated for every sample taken 
(based on an idea by Michael Andrews)
- the count value is increased for the final render to 1200 (which 
results in the additional samples taken in the parts marked blue in

http://www.tu-bs.de/~y0013390/files/rad_01e2.png

to be gathered with this count value.  Of course this is significantly 
slower (~11min here) but the result:

http://www.tu-bs.de/~y0013390/files/rad_01g1.png

seems quite comparable to your latest C4D test concerning artefacts.

Note the C4D are much closer to the correct result than this but for a 
nice looking image this is not the most important thing.

Some additional notes: Of course these settings are especially tweaked 
for this scene - for actual use it would be nice to have settings that 
are easy to adjust without doing dozens of test renders.  The 'double 
count' trick can be simulated in standard POV using a two pass render 
and simply changing the count value in the scene file.  Of course it 
also depends on the low_error_factor technique used - i don't know the 
effect if you use it with other values.  The random rotation of samples 
was originally developed by Michael Andrews for a scene with a linear 
light source (neon tube) for which this is a very useful technique.  For 
many indoor scenes with flat walls this is probably useful although it 
also can lead to worse results in other situations.

> What seems certain now is that both POV-Ray and C4D use the same basic
> algorithm. C4D also has an "always_sample off" option (didn't try it). What
> it doesn't have is the equivalent of mosaic preview (it's always like a
> pixel per pixel pretrace). It does have, when the quality is high, a lag
> time before the pretrace starts (POV-Ray does this too). It can do partial
> radiosity renders (in the modelling view only - POV is much more flexible
> when it comes to partial renderings, but I'll explain more when I know C4D
> enough to make educated comparisons). I'm not sure how far these comparisons
> can go anyway, because part of the speed difference could very well be
> explained not by a faster radiosity algorithm, but simply by the use of scan
> line.

I am not sure if C4D uses scanline techniques for this kind of render at 
all.  And if it does it will probably not change much because more than 
90% of the time are spent for radiosity calculations and the shadows are 
probably raytraced as well.  Also note in a real scene with very 
detailed geometry the advantages of scanline are lower.  Not to mention 
reflecting and refraction objects.

Christoph

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Last updated 25 Oct. 2003 _____./\/^>_*_<^\/\.______

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