Rtcontrib with ies2rad

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

Luminaire rad file for the first row (from ies2rad):

···

#################################################

void brightdata y_down1_dist

5 flatcorr y_down1.dat source.cal src_phi4 src_theta

0

1 6.52358

y_down1_dist light y_down1_light

0

0

3 1 1 1

y_down1_light polygon y_down1.d

0

0

12

      -24 -1.98 -0.00984252

      -24 1.98 -0.00984252

      24 1.98 -0.00984252

      24 -1.98 -0.00984252

y_down1_light polygon y_down1.u

0

0

12

      -24 -1.98 0.00984252

      24 -1.98 0.00984252

      24 1.98 0.00984252

      -24 1.98 0.00984252

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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" <[email protected]>
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

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: [email protected]
[mailto:[email protected]] 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" <[email protected]>
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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