[Radiance-general] Understanding rtcontrib

[Axel Jacobs]

Dear all,

I've been reading some of the very interesting presentations from the 
last Radiance workshop and am now keen on finally getting to the bottom 
of this rtcontrib thing.

My aim is to do Dynamic Daylight Simulations, DDS, using rtcontrib 
rather than DaySim.

As I am going along, I am preparing more material for the Advanced 
Tutorial. A usual, the notes advance at a leisurely pace, trying to make 
one little mistake or discovery a time, rather than doing them all at once.

I have put up some very early notes (really only just scribble with some 
images) here:
http://luminance.londonmet.ac.uk/pickup/rtcontrib_lesson.html
and would be grateful for any feedback.

This is what's there at the moment:

- show that rpict is simply a convenient way of calling rtrace to 
produce an image
- show that rtcontrib is a souped-up version of rtrace (bear with me 
before banging your head against the wall over this one)
- show how rtcontrib produces individual images based on light source 
modifiers
- show how this can be extended to different 'zones' using binning, e.g. 
for daylight coefficients

I have not looked at the mkillum-like functionality of rtcontrib yet 
(pseudo-forward-raytracer?), and the model you see in the images doesn't 
even have a window pane.

All images under a glow sky (not the ones with circular 11deg light 
sources) have an overcast distribution. Eventually, this should probably 
be a simple glow without any distribution assigned to it, but I've used 
a gensky material for now to be able to compare the absolute values of 
the combined results which should match the rpict ones.

The big show stopper so far is that I don't get the absolute values 
right for a glow sky with Tregenza subdivisions. You will also see just 
how weird the sky hemisphere looks in this simulation after the 145 
patches have been combined.

Any hints are very welcome.

Cheers

Axel