[Radiance-general] DAYSIM vs. Radiance illuminance values

[Nicolas Roy]

Hi Jan,

Thanks for the input. I've used gendaylit and performed the calculations 
again, results now show an average difference of 3-4%. I'm glad I could 
find an update for gendaylit that supports Cygwin on the Fraunhofer site.  


-Nicolas








Jan Wienold <jan.wienold at ise.fraunhofer.de> 
Sent by: radiance-general-bounces at radiance-online.org
22-09-2008 16:40
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Re: [Radiance-general] DAYSIM vs. Radiance illuminance values






Hi Nicolas,

Daysim is using the Perez Sky model, so I would use gendaylit instead of 
gensky for a comparision. 
Secondly, I assume, that you have to use the -R instead of the -r Option, 
since you are dealing with irradiance rather than radiance. This is 
causing the big difference, I assume.
But  be careful: -R is expecting horizontal direct irradiation, not direct 
normal irradiance!

Jan

Nicolas Roy wrote: 

Hi, 

I'm making a short comparison between illuminance values obtained in 
DAYSIM and Radiance for a specific day/time, and the results I obtain show 
a  ratherbig difference with Radiance having values twice as high. 

I compare the values in the annual illuminance profil (.ill) generated by 
DAYSIM, with values I obtained in Radiance for the same day/time. I 
defined the Radiance sky description using the "direct normal irradiance" 
and the "diffuse horizontal irradiance" values from the climate data used 
in DAYSIM. 

What can be the source of such large differences? 


I use the following in Radiance: 

##sky 

gensky 6 21 12.5 -a 52.47 -o -15.4 -m -15 -r 35 -B 363 > sky001.rad 


##out.rad 

skyfunc glow sky_glow 
0 
0 
4                0.9                0.9               1.15  0 

sky_glow source sky 
0 
0 
4                  0                  0                  1 180 

#a green ground 
skyfunc glow ground_glow 
0 
0 
4                0.2                        0.2               0.2  0 

ground_glow source ground 
0 
0 
4                  0                  0                 -1 180 

##rtrace rcalc run 

oconv sky001.rad out.rad material.rad geometry.rad > 001.oct 
rtrace -w -h -I+ @options.opt 001.oct < sensors.inp | rcalc -e 
'$1=($1*0.265+$2*0.670+$3*0.065)*179' > 001.ill



-Nicolas 









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