[Radiance-general] experiences with the photon map

[Bissell, Andrew]

Shortly after PMAP was released I messed about with it to try and
understand what the numbers all meant and to see what you had to do to
get accurate results.  I have cut down a presentation I created to
provide 4 slides of the process I went through to get appropriate images
and numbers.  Not very scientific to be honest but perhaps a starting
point for further study.

I will go and have another look at the same model with alternative
suggestions for the three variables if you have any.  Although I may
already have the results as only some of them are included here.

Regards

Andrew
__________________________
Andrew Bissell
B.Eng(Hons) C.Eng MSLL MCIBSE MIET
Associate Lighting Designer
Cundall Light4
Direct: 0161 200 1235
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-----Original Message-----
From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Lars
O. Grobe
Sent: 04 December 2008 08:01
To: radiance-general at radiance-online.org
Subject: [Radiance-general] experiences with the photon map

Hi list!

While I am trying this on Radzilla now (as there is no photon-mapping
available in Radiance-3.9 at the time of this writing), I am pretty sure
that the effects I get are not related to Radzilla but on the way I use
the pmap-System.

I am trying to model a simple, highly specular horizontal light duct,
with a rectangular cross-section (yes I know that in THIS case I could
use the mirror material and Radiance, but I will go for non-planar
surfaces later).

Now either I get very splotchy luminance images in the inside, or,
increasing the `bandwith` to rather high values, have a blurry result
with - and this is the problem - light leaving the geometry even though
it is closed (the duct has a 45 degree mirror at its end that should
actually close it, but the sides extend besides the mirror and appear
illuminated even behind it).

I am working with an initial photon count for both global and caustic
photons of 2.000.000 and a bandwith value of 2000 at the moment.

Is it possible to get such systems rendered in a way that I have both a
smooth luminance and no light escaping the geometry?

Is there any source for a starting point in what way rtcontrib could be
used for modeling such systems? I know the qt-movie from the workshop,
but I did not get it - and it seams that I know noone except Greg who
got it so far ;-)

Thank You & CU, Lars.


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