[Radiance-general] Rtcontrib with ies2rad

[Andrew McNeil]

Yay! It works, Thanks!  I should have known to go straight for the
Head...

I'm surprised at how easy it is to use rtcontrib.  I've been avoiding it
for almost year because I assumed it was complex, but not so!  Kudos
Greg.



-----Original Message-----
From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of
Gregory J. Ward
Sent: 23 May 2006 14:25
To: Radiance general discussion
Subject: Re: [Radiance-general] Rtcontrib with ies2rad

Hi  Andrew,

You aren't really doing anything wrong, but the problem is that  
rtcontrib reports the contribution *coefficients*, which is not the  
same thing as the contributions.  To get contributions, you need to  
download and compile the latest HEAD release, and use the new -V  
option to rtcontrib.  Then, you should get the results you expect.   
This is a subtle point that I actually missed in the design of the  
program, which is why the option was only added more recently.  Here  
is the description from the new man page:

>        By setting the boolean -V option, you may instruct rtcontrib  
> to  report
>        the  contribution  from  each material rather than the ray  
> coefficient.
>        This is particularly useful for light sources with   
> directional  output
>        distributions,  whose  value  would  otherwise  be lost in  
> the shuffle.
>        With the default -V- setting, the output of rtcontrib is a   
> coefficient
>        that must be multiplied by the radiance of each material to  
> arrive at a
>        final contribution.  This is more  convenient  for   
> computing  daylight
>        coefficeints,  or  cases where the actual radiance is not  
> desired.  Use
>        the -V+ setting when you wish  to  simply  sum  together   
> contributions
>        (with  possible  adjustment  factors) to obtain a final  
> radiance value.
>        Combined with  the  -i  or  -I  option,  irradiance   
> contributions  are
>        reported  by  -V+ rather than radiance, and -V- coefficients  
> contain an
>        additonal factor of PI.

Hope this helps.
-Greg

-----------------
> From: "Andrew McNeil" <Andrew.McNeil at arup.com>
> Date: May 23, 2006 5:44:59 AM PDT
> Hi everyone,
>
> I've finally gotten around to using rtcontrib and am having a  
> little difficulty.  I have 5 rows of luminaires and am trying to  
> calculate the illuminance contribution from each row of luminaires  
> to a grid point.  To test my model, I am first calculating only the  
> direct component from the luminaires to the points.
>
> The command I'm using is as follows:
>
> rtcontrib -I+ -ab 0 -o out.dat -m y_down1_light -m y_down2_light ...  
> model.oct < grid.pts
>
> I've pasted the luminaire file for the first row of luminaires at  
> the end of this email for reference.
>
> I expected that the sum of the rtcontrib output values would be the  
> same as he output from a straight rtrace calculation.  What I got  
> when I summed the rtcontrib output was 3% of the rtrace calculation  
> ( 18 vs 530 ).  After some experimentation, I found that I get the  
> same value (18) with rtrace if I remove the brightdata modifier  
> from the light primitive (replacing "y_down1_dist" with "void" in  
> the luminaire file).  So I figured I must have been using the wrong  
> modifier in my rtcontrib command.  But, when I tried other  
> modifiers (y_down1_dist and y_down1.d) rtcontrib returned zeros.
>
> So to finally get to the point, what is the correct modifier to use  
> in rtcontrib to get the illuminance contributions WITH the  
> brightdata photometry?  Or maybe there is something else I'm doing  
> wrong?
>
> Cheers,
>
> Andrew
>

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