Actually, Jensen (the guy who originated the photon map technique) has used
photon maps quite successfully with full global illumination.  In my
preliminary tests, I did not find such good results, but I've learned more
about photon mapping since then.

His techniques use a global photon map to improve the speed of the 
gradient-cached MC tecnique (which is what POV uses).  POV does use MC, but
it uses many samples rays per sample point and then interpolates between
sample points.  Adding photons to this means that you use the photon data
to direct the sample rays so that you can use fewer rays with equally good
results.  Relatively few photons are needed to achieve this.  Also, this
technique can achieve more than one level of indirectness by directly
visualizing the photon map after the first bounce (and the photon map
already has many levels of indirectness incorporated already).

I haven't done this yet because I don't fully understand how POV's
radiosity works (the code is not well commented, IMHO).  Is the original
author around to help explain it to me?  Does anybody (Ron?) have links
to Ward's papers on this topic?

-Nathan

Margus Ramst wrote:
> 
> Having seen the results of similar techniques in GI, i'm a tad sceptical. While
> such a method can be very accurate, I believe it would necessitate Monte Carlo
> sampling - threreby introducing a lot of noise in the image. Think of the
> current media that uses a similar technique.
> The beauty of the current GI method is that it's relatively easily integrated
> into the POV engine. If you want something better, I would prefer true
> radiosity. Implementing this, however, is a daunting task - probably more so
> than the photon approach. In particular, it would require meshing the scene into
> discrete patches. I'm not sure if Radiance's wavelet method, though... Anybody?
> 
> Margus
>

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