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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