[Radiance-general] PMAP simulation

[Roland Schregle]

Jan Wienold wrote:

> 1. To distribute photon and store them in files (global and caustic photons separately) 
 > e.g.
> ~/bin/radiance/pmap/mkpmap  -apg f81_z.gp 700000 -apc f81_z.cp 700000  test.oct
> 700000 is the number of the photos emitted, gp : global photons, cp caustic photons

Actually, it's the number of *stored* photons, which is what the user 
really wants. The resultant number of emitted photons is usually much 
larger.

>  Of course, the ambient options don't make really sense
> since the ambient calculation is replaced by the forward raytracer.

They do to some degree: the RADIANCE pmap uses a final gather, which 
means *one* ambient bounce is performed (if -ab > 0, regardless of 
actual value), with pmap lookups resulting for each sample ray. 
Consequently, the -ad, -ar, -aa params are still valid. They are *not* 
used for caustics, however.

> In many cases, the use of the photon port mechanism is extremely useful. 
> With photon ports you can define materials, through which the light 
> enters the scene. A typical example is an office scene, which is lit by 
> the sky. Using this, you can avoid huge effort, since the photons are 
> distributed mostly in "relevant" directions. In your case it could make 
> sense to define the entering cross section as "photon port". You can use 
> e.g. glass material with refraction index 1 (==air!!) without disturbing 
> the simulation.

Photon ports are a must for light pipes, unless you stick a light source 
right in front of the aperture (which would be a fake). An invisible 
port can simply be declared with antimatter -- see the lightpipe scene 
in the example tarball on the pmap page (URL below).

> Good luck!

Ditto! :^)

-- 
Roland Schregle
PhD candidate, Fraunhofer Institute for Solar Energy Systems
RADIANCE Photon Map page: www.ise.fhg.de/radiance/photon-map

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