[Radiance-general] daylight factor and rtrace cmd

[Guglielmetti, Robert]

Valere, as Chris and Thomas have mentioned, you want to use the -i option for that field.

Honestly, I've never noticed this -I option before. The man page doesn't mention the 1m offset, either. Frankly, I don't understand the point of this option. If I want irradiance, I usually want it on some surface or virtual plane (a uniform grid on the front of a library stack, for example), and I just make a field of points normal to that surface and use the -i option to compute irradiance at that point. If for some reason I wanted irradiance offset from some surface (dark sky / light pollution calc or something), I would just arrange the points offset from the surface, and oriented at the surface, and still use the -i. What are people generally using the -I option for? I'm curious.

Robert Guglielmetti  IES, LEED AP
Building Energy Efficiency Engineer 
National Renewable Energy Laboratory (NREL)
1617 Cole Blvd, MS-5202
Golden, CO 80401
robert.guglielmetti at nrel.gov
303.275.4319

-----Original Message-----
From: radiance-general-bounces at radiance-online.org [mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Thomas Bleicher
Sent: Thursday, July 16, 2009 10:46 AM
To: Radiance general discussion
Subject: Re: [Radiance-general] daylight factor and rtrace cmd

As Chris wrote, -I implies an observer point 1m above the 'point of interest'.
But it also turns around the view vector (your output shows -1.000000e+000).

Basically rtrace introduces a virtual plane of lambertian properties and looks
down onto this plane to calculate the irridance from the reflection (which is
identical).

The offset of 1m is only a problem if you want to use the output to anchor
your results in a model or if your workplane is close to an obstruction that's
lower than 1m above the plane. Then the rtrace rays would hit the back
of the obstruction and not the ideal reflector.

But then, perhaps Greg has anticipated this case and added some magic to
avoid it ...

Thomas


On Thu, Jul 16, 2009 at 5:17 PM, PAUPELIN-HUCHARD
Valere<v.paupelin-huchard at elioth.fr> wrote:
> Hello,
>
> I'm trying to do daylight factor calculation. I am observing a 1
> meter height offset between my workplan point file which is already at 0.85m
> above the floor (*.fld) and the rtrace result (*.irr).
> Someone would tell me why?
>
> the command used is:
> rtrace -ab 7 -ad 2048 -oodv -I
> rcp.oct<numeric/plan_de_travail.fld>numeric/090715_BU_Rennes_07_vitrage_irradiance.irr
>
> four first lines sample of the files:
>
> plan_de_travail.fld:
> x          y         z         o
> 0.50     -0.25     1.84     0 0 1
> 0.50     0.00      1.84     0 0 1
> 0.50     0.25      1.84     0 0 1
> 0.50     0.50      1.84     0 0 1
>
> 090715_BU_Rennes_07_vitrage_irradiance.irr
> x                        y                        z
> o
> r                         g                         b
> 5.000000e-001    -2.500000e-001     2.840000e+000
> 0.000000e+000 0.000000e+000 -1.000000e+000     1.406147e-001
> 1.406147e-001     1.406147e-001
> 5.000000e-001     0.000000e+000    2.840000e+000
> 0.000000e+000 0.000000e+000 -1.000000e+000     1.581891e-001
> 1.581891e-001     1.581891e-001
> 5.000000e-001     2.500000e-001     2.840000e+000
> 0.000000e+000 0.000000e+000 -1.000000e+000     1.765201e-001
> 1.765201e-001     1.765201e-001
> 5.000000e-001     5.000000e-001     2.840000e+000
> 0.000000e+000 0.000000e+000 -1.000000e+000     1.890535e-001
> 1.890535e-001     1.890535e-001
>
> I am afraid my daylight factor result are not valid at the height of 1.84m
> but at 2.84m, am I wrong?
>
> Thanks,
> Valere.
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
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>
>

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