[Radiance-general] rtcontrib

[Greg Ward]

Hi Jia,

I will answer your questions the best I can inline...

> From: Jia Hu <hujia06 at gmail.com>
> Date: July 14, 2011 9:12:12 AM PDT
> 
> Thank you! I have other questions related to this program.
> 
> (1) Question 1:
> 
> In the case that both of "-f", "-b" and "-m" are used, the .cal algorithm and "-b" option are applied to objects with "-m" materials, for example, 
> 
> vwrays -ff $vw |rtcontrib @image.opt -ffc $(vwrays -d $vw) -f tregenza.cal -b tbin -o images/patches/p%03d%s.hdr \
> -m sky_glow -m ground_glow -w testroom_whitesky.oct
> 
> If I replace "ground_glow" with "ceiling_mat", the .cal will applied to "ceiling" geometry and divide ceiling into many patches according to the ray direction and intersection with ceiling? 

Yes, the bins will still be based on ray direction due to the "tbin" definition in "tregenza.cal", but will apply to rays striking surfaces using "ceiling_mat" instead of "ground_glow".  The intersection position on the ceiling will not affect "tbin" since it doesn't use this information, so the same direction at one corner of the ceiling will go to the same bin as a ray hitting the opposite corner in that direction.

> 
> (2) Question 2:
> 
> Assume my model has two windows in the south wall and one sensor in the interior building, and I wish to calculate the daylighting coefficient of each patch of sky and each window to the illuminance at the sensor point. The result is like a matrix as follows:
> 
>                     SkyPatch001,       SkyPatch001,       
> Window01     coefficient (RGB)   coefficient (RGB)
> Window02     coefficient (RGB)   coefficient (RGB)
> 
> Each coefficient shows the contribution of each sky patch and each window to the sensor illuminance. Can I achieve this in one rtcontrib command?
> Is the following expression right?
> 
> [input ray] | rtcontrib -f tregenza.cal -o window_%s.data -b tbin -m window01_mat -b -b tbin -m window02_mat  [other necessary options] 

You don't need to give the "-b tbin" option twice, and the "-b" option by itself will generate an error, but otherwise it is OK.  Note that this command neglects any exterior obstructions that might interfere with the travel of a sample ray from the exterior of the window to the sky.  If your building has external shades or obstructions outside, the above technique will not produce accurate results.

The general ability to choose combined interactions in rtcontrib is lacking.  E.g., you can't ask for all rays that pass through "window1" then go on to intersect "building2" and reflect to "skypatch17".  It would be a useful feature to add, but such accounting is problematic.

Best,
-Greg