[Radiance-general] rtcontrib

[Gregory J. Ward]

Hi Santiago,

I wish I could offer you some words of encouragement, because I  
appreciate the difficulty you face applying rtcontrib to daylight  
coefficients.  The truth is, you really need some scripts to help out  
with the task, and I haven't yet had a chance to write a general set  
of scripts or an executive program for DC analysis.  I am working on  
this project currently, as a matter of fact.

All I have at this point is a few test scripts I assembled for a  
daylight simulation study, and I can make these available for you if  
you need an early start on this.  If you can wait a few weeks, I will  
have something much better, I hope.

Just to answer your question, adding together the rtcontrib outputs  
directly gives you the result for a uniform sky.  To get a particular  
sky, you must multiply each image by the average radiance of the  
corresponding sky patch.  To compute this, a simple rtrace  
calculation using the desired sky model and a set of randomly  
distributed rays over the hemisphere will do the trick.  Such a set  
of rays is given in the file "ray/lib/tregsamp.dat", where there are  
64 rays per sky patch.  The command to compute pcomb arguments from  
this file is:

rtrace -h skymodel.oct < tregsamp.dat \
         | total -64 -m \
         | rcalc -o '-s ${$2} c_${recno-1}.pic'

I realize this is just a clue, but if you wait a few weeks, hopefully  
I can provide a complete solution.

-Greg

> From: Santiago Torres <tiago at tkh.att.ne.jp>
> Date: October 30, 2005 2:21:32 PM PST
>
> Hello,
>
> I've been trying to use daylight coefficients with rtcontrib and I  
> have a couple of questions.
> I made images with the contribution of each sky patch, but the  
> images look quite noisy, and if I combine them I don`t get the same  
> as if I was rendering the scene altogether.
> The command I used is like this:
>
> vwrays -ff -x 500 -y 500 -vf vint.vf | rtcontrib -ffc `vwrays -d -x  
> 500 -y 500 -vf vint.vf` -ab 5 -ad 2048 -as 1024 -b tbin -o c_%d.pic  
> -m skyglow -f tregenza_h.cal scene.oct
>
> If necessary I can post some images, but probably it`s something  
> obvious I`m missing here...
>
> My second question is regarding the calculation of model skies  
> (like Perez) with the rtcontrib results. Perez sky gives the  
> luminance value at a certain point, but I guess in order to  
> multiply the contribution of a certain section of the sky, I need  
> to integrate the luminance values inside that section. Is this  
> correct? Can anyone point me to any reference where this might be  
> explained more? Any ideas about how to implement this in a script?
> Thank you in advance. Best regards,
>
> Santiago