[Radiance-general] Rtcontrib with ies2rad
Gregory J. Ward
gregoryjward at gmail.com
Tue May 23 15:24:52 CEST 2006
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
>
More information about the Radiance-general
mailing list