"Colin" <nomail@nomail> wrote:
> So what I'm looking for is if you were tracing photons, how many per unit area
> strikes a particular position on a surface. We usually measure this in things
> like W/m2 or lux (lumens/m2).

That's basically what an orthographic shot of the surface with photon mapping
will give you: A bitmap specifying how many photons have hit which point.

If you crank up the number of photons high enough, you can probably get any
precision you may need.

(At least if you make sure that gamma correction is turned off, and your light
brightness has a proper brightness to represented by the output image format
you choose.)

To my knowledge, the principle behind this is extremely simple: PoV will shoot
photons, remember where they hit, and increase the brightness of the object
accordingly.


The only problematic thing with this might be if the light source itself is
directly visible from your "test surface", as you want to eliminate the (most
likely not really exact) conventional lighting. I don't know by heart whether
you can turn off conventional lighting completely and just use photon mapping.


A more brute-force attempt would be to do the same thing with radiosity, which
basically does the very same thing "backwards" and should lead to the same
results given extremely high-quality settings), but is probably a waste of
computing power for this application.

If it cannot be helped otherwise, it would always be possible to do something
with the trace() function, but something built-in will most likely be a lot
faster.

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