[Radiance-general] Gendaylit overcast sky underestimation issue

[Jan Wienold]

Hi Jack,

you missed obviously something important - either you missed to generate 
the sky (then you have just the sun influence) or you made a mistake in 
using rtrace.
It has nothing to do with gendaylit.

you need a sky description like this:

skyfunc glow sky_glow
0
0
4 1 1 1 0

sky_glow source sky
0
0
4 0 0 1 180

skyfunc glow ground_glow
0
0
4 1 1 1 0

ground_glow source ground
0
0
4 0 0 -1 180

putting that into an octree:

oconv -f new.sky outside.rad >test.oct

and then call rtrace using the -I and -ab 1 option:

echo 0 0 0 0 0 1 |rtrace -h -I -ab 1  test.oct | rcalc -e 
'$1=47.4*$1+120*$2+11.6*$3'

Then you get: 17572.5875 lux.

Best,
Jan














On 03/21/2012 09:34 AM, Jake Osborne wrote:
> As part of a project I am comparing measured data from both Berkeley 
> and the Isle de la Reunion to simulated illuminances under the Perez 
> sky model in both Radiance and 3ds Max Design, however Gendaylit seems 
> to be producing incorrect sky descriptions for the overcast days in 
> the dataset. I am wondering if I am missing something critical.
>
> Below is the command I am using to produce a sky description, for 
> 10:30am on a particularly overcast winter day in Berkeley, with the 
> measured direct radiation being 0.15W/m^2 and the measured diffuse 
> being 155.13 W/m^2:
>
> gendaylit 12 4 10.5 -W 0.15 155.13 -g 0.2 -a 37.88 -o -122.25 -m -120 
> > new.sky
>
> This produces a sky that when simulated (using rtrace, with the -I 
> option, and multiplying by 179) only gives a global horizontal 
> illuminance of ~12lux, rather than the expected ~19,000lux.
>
> Using the -O option with a value of 2 produces a significantly 
> brighter sky providing ~800 lux, still far from what I am expecting.
>
> Hopefully someone can spot the problem straight away;
>
> Cheers,
>
> Jake Osborne
>
>
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> Radiance-general at radiance-online.org
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-- 
Dr.-Ing. Jan Wienold
Head of Team Passive Systems and Daylighting
Fraunhofer-Institut für Solare Energiesysteme
Thermal Systems and Buildings
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49(0)761 4588 5133 Fax:+49(0)761 4588 9133
jan.wienold at ise.fraunhofer.de
http://www.ise.fraunhofer.de

In office:
Mo,Tue: 8:30-18:00
We,Thu: 8:30-16:00
Fr:  8:30-15:30

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