[Radiance-general] Luminance predictions in a plane

[Greg Ward]

This seems to be a repeat posting of something sent out on Saturday.   
There is no need to post things twice -- we did get it the first  
time.  If you are unsure if a posting has made it to the list, you  
can always go online to check:

	http://www.radiance-online.org/pipermail/radiance-general/

I did not reply to this right away, since it is really a basic  
question, and I figured any number of people could handle it.  In any  
case, a careful reading of the rtrace man page should give the  
answer.  Quoting from the first paragraph of:

	http://radsite.lbl.gov/radiance/man_html/rtrace.1.html

"Input for each ray is:

             xorg yorg zorg xdir ydir zdir
"

You simply start the ray an arbitrary distance from your surface and  
give it a vector corresponding to the desired luminance measurement.   
The returned values (when you run rtrace without the -I+ option) will  
be in SI radiance units (watts/sr/meter^2),which may be converted to  
luminance (in candelas/meter^2) using the formula specified under the  
"Examples" section:

	rtrace  -h  scene.oct  <lum_meas.pts |  rcalc  -e '$1=47.4*$1+120*$2 
+11.6*$3'

I hope this helps.
-Greg

> From: sokol dervishi <dervishi_sokol at yahoo.com>
> Date: May 19, 2008 7:31:27 AM PDT
>
> Dear all,
>
> I have a question regarding the luminance prediction (cd/m2) on the  
> plane for certain points. and any help would really be appreciated.
>
> I have measured  certain points with an luminance meter. I have  
> used also image-based for the same points to extract the luminance  
> and I have very similar results. I need to use also simulation- 
> based luminance values for the same points and compare the results  
> with the measured and image based ones.
>
> Before,  I have simulated only Illuminances. How can I measure the  
> Luminances?
>
> Here is the code I use to predict the illuminance:
>
> # commands to run
> commands = ["rm -f /tmp/bpi.amb",
>             "oconv env.rad lab_surfaces_corrected_moved.rad  
> lab_windows_and_doors.rad strato_sokol2.rad> lab.oct",
>
> "echo '4.52    0.85 0.74 0 0 1 " +
>         "3.74    1.13 0.74 0 0 1 " +
>         "4.52    1.13 0.74 0 0 1 " +
>         "5.30    1.13 0.74 0 0 1 " +
>         "3.74    2.13 0.74 0 0 1 " +
>         "4.52    2.13 0.74 0 0 1 " +
>         "5.30    2.13 0.74 0 0 1 " +
>         "3.74    3.13 0.74 0 0 1 " +
>         "4.52    3.13 0.74 0 0 1 " +
>         "5.30    3.13 0.74 0 0 1 " +
>
>
>             "' | rtrace -w -af /tmp/bpi.amb -as 512 -ar 64 -aa 0.15  
> -ab 2 -I+ -h lab.oct | rcalc -e '$1=($1*0.265+$2*0.670+$3*0.065)*  
> 179'",
>
>
>             ]
>
>
> Any help would be really appreciated,
>
> Thank you very much
>
> Best regards,
>
> Sokol Dervishi