[Radiance-general] Irradiance on tilted surfaces discarding downwards rays

[Victor LRG]

Dear all,

I was wondering if there is a simple way in Radiance to calculate
irradiance (rtrace -I) on a tilted surface, but discarding the rays that
are fired downwards, aiming below the horizon. I guess it can be done
manipulating the source code, but I cannot think of a simple way.

Perhaps it could be done inverting the initial ray, measuring the luminance
of the surface by using a lambertian white material with an altitude
modifier, and calculating then the illuminance, but it is a bit convoluted
and the white material may distort too much the real lighting levels in the
scene.

Any ideas?

Thanks,

Victor Lopez-Rioboo Gil
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