[Radiance-general] experiences with the photon map

[Lars O. Grobe]

Hi Jan!
> I'm pretty sure its a question how you modeled the end of your "light-pipe".
> Photon mapping is doing an density estimate to calculate the radiance
> and is searching for photons in the nearby.
> Unfortunately the algorithm is doing this also for surfaces , which are
> "leaving" a closed space. For example, if you have a closed box and you
> add a surface to the scene, which is half inside and half outside the
> box, you will get light into the box.
> You can avoid this phenomena, if you really "close" your pipe (I assume
> so  ;-)  ).
>   

Well the pipe is closed by the 45 degree mirror, but I guess that I must 
not have geometry extend from the end (so that a part of it is inside 
the system and a part is outside). This is really important for 
modelling and was not clear to me so far! So the viewer in the sketch 
below will see the surfaces A and B lid even though light is not able to 
reach those, because the photons hitting the surface are counted even 
though not visible from the viewer position, right?

Surface A
___________________________
                          |
light source      |    viewer
________________|___________

Surface B

> By the way, we will probably update photon-mapping for the 3.9 version
> (or the 4.0) version within the next half year, fixing also some bugs.
> This depends on a new project probably launched in January.
>   
This is good news for all Radiance users! Will it be possible to use 
BRTDfunc modifiers with the photon map than? At the moment we have a 
strange situation - most Radiance users most probably use the software 
for advanced daylighting simulation. But they cannot model the advanced 
systems with the core distribution (pmap is not integrated), and even if 
they patch Radiance to support photon mapping, they cannot use the 
galzing definitions as given e.g. by the glaze script because of a lack 
of support for BRTDfunc in the pmap extension. I wonder how one can 
model a daylight set-up with light redirection systems in Radiance at 
all at the moment.

How are experiences with the pmap for Radiance 3.8? I could use that one 
for now (I cannot really wait for half a year, so I must use what is 
available) if it is found to have been relieable. Or should I stay with 3.7?

Again thanks to you and the other Fraunhofer folks making this important 
extension available to us - is there any hope that pmap could become 
part of the Radiance distribution itself one day?

CU, Lars.