pmap mkillum

Hi Carsten, hi list,

In your pmap-tutorial (1), you combine pmap and mkillum in your last example. As far as I understood, the illum face would actually block the sun's photons being emitted from the outside. So I do not really get the set-up.

I have the case of a glazing with integrated blinds. So far, I put an antimatter surface into the window frame (just 2.5 cm outside the outer glass pane) as a photon port. That way, the blinds are INSIDE, and the photon distribution accounts for their redirecting effects.

Now, I would usually put a mkillum-face into the inside of the frame, to get all the amb interreflection calculation for the blinds done before rendering the picture. Would this lead to valid results? Would the global and caustic photons pass the illum generated by mkillum? If yes - do only caustic photons, or both caustic and global photons pass the illum surface? Does this result in double-counting?

thanks&CU Lars.

(1) picture 9


oh well, this is more than 2 years ago...

The clue to understand pic 9 of the tutorial is, that it was generated in several steps

1) generate a caustic photon map for the sun and skylight redirected by the metal slabs

2) run mkillum with an illum face in the opening, to get external sky light and ground reflection (note: the slabs are on the inside, so they┬┤re not included in the mkillum distribution)

3) run radiance/radzilla with the illum source and the previously generated photon map.
The illum source lets direct sunlight pass through, the photon map brings in the redirected light due to the slabs, and all further distribution is then handled via the normal ambient calculation

(by the way, I have to check one detail again: in which way the specular part of the metal slab reflection acts within the normal ambient calculation together with the illum source, i.e. if there is the risk of some overcounting in this approach....)


So if I get it right...

I first place a surface to the outside of the slabs as a photon port
(for caustics only) and distribute the caustic photons in my scene, save
the map.

Second I create a mkillum-source. Can I put this to the inside of the
redirecting system to accelerate later ambient calculation?

Third I render my image, the direct light sources are already in there
as caustics (because the pmap had been saved), and visible for the
direct calculation.

If I use a void-modifier for the surface that mkillum will convert into
an illum, I can have it in the scene when distributing the photons,
right? The photons pass a void-surface, don't they?

So the only point is to have a

rzpict -apem .... > null

at the beginning, similar to an ouverture calculation, to fill the
pmap-file for caustics? Than I call


and after that


again, but without the need to modify my scene files at all?

What happens if I have also generated a global pmap in the first step?
Would this lead to have the illum ignored? Or would I get
double-counting, as there are already global photons in the scene
representing the indirect illumination, and the illum-face adds the same
amount into the scene acting as a direct light source?

Hope I got it now... :wink:


P.S.: I still did not understand what happens if I define a caustic map,
but no global map. In this case, is the indirect calc done like in
classic, and only the direct calc gets the caustic photons added?