Hi

Could someone please explain, how pretrace_start affects the quality of the
final image? Radiosity pretrace phase is mentioned quite shortly in
documentation and tutorials, and only pretrace_end gets explained. As far
as I understand, the difference between pretrace_start and pretrace_end
specifies the number of pretrace steps. E.g if I specify pretrace_start
0.08 and pretrace_end 0.01 there will be 4 steps. But will there be any
difference if I e.g. specify pretrace_start the same as pretrace_end, and
there will be only one step?

--------------------------
Andrey

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The pretracing does preliminary passes on the scene to place and gather
radiosity sample for reuse. The idea is that when beginning with broad
sweeps, you begin with placing samples all around the image for starters,
and then, the more iterations (and also the more detailed the pretrace gets)
you do, the more samples are placed where needed. It's a refinement process.
As with all refinement processes, starting with highly detailed settings
right away doesn't harm, though I think it is better to have a few passes
for the radiosity algorithm to properly figure out where to place samples.

What I personally like about the pretrace is that you can get a good feel if
the lighting is right, cause you get a rough render very fast.

Regards,
Tim

-- 
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>

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Andrey Platonov nous apporta ses lumieres en ce 2005-09-16 15:57:
> Hi
> 
> Could someone please explain, how pretrace_start affects the quality of the
> final image? Radiosity pretrace phase is mentioned quite shortly in
> documentation and tutorials, and only pretrace_end gets explained. As far
> as I understand, the difference between pretrace_start and pretrace_end
> specifies the number of pretrace steps. E.g if I specify pretrace_start
> 0.08 and pretrace_end 0.01 there will be 4 steps. But will there be any
> difference if I e.g. specify pretrace_start the same as pretrace_end, and
> there will be only one step?
> 
> --------------------------
> Andrey
> 
> 
> 
> 
In some cases where you get artefacts near corners, a slight change in pretrace_start
may supress 
those. Changing the pretrace_start value cause the location of the samples to shift
slightly and 
possibly miss the problem pixel(s).
Using smaller pretrace_end can realy help improve the quality of the radiosity while
still using 
lower, and faster, parameters.
I like to use a variable to set my pretrace, by itself for _start, divided by a power
of 2 for the _end.

Alain

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"Tim Nikias" <JUSTTHELOWERCASE:timISNOTnikias(at)gmx.netWARE> wrote in 
message news:432b29f5$1@news.povray.org...
> The pretracing does preliminary passes on the scene to place and gather
> radiosity sample for reuse. The idea is that when beginning with broad
> sweeps, you begin with placing samples all around the image for starters,
> and then, the more iterations (and also the more detailed the pretrace 
> gets)
> you do, the more samples are placed where needed. It's a refinement 
> process.
> As with all refinement processes, starting with highly detailed settings
> right away doesn't harm, though I think it is better to have a few passes
> for the radiosity algorithm to properly figure out where to place samples.
>
> What I personally like about the pretrace is that you can get a good feel 
> if
> the lighting is right, cause you get a rough render very fast.

   Thank you Tim.

     ~Steve~


>
> Regards,
> Tim
>
> -- 
> "Tim Nikias v2.0"
> Homepage: <http://www.nolights.de>
>
>

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Thanks everybody.

--------------------------
Andrey

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