DAYSIM vs. Radiance illuminance values

radiance-general
1

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

[email protected]

2

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

[email protected]

------------------------------------------------------------------------

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

3

Dear Nicolas:

I agree with Jan that using gensky and comparing the results with Daysim
is a bit meaningless. As far as accurate Daysim accuracy compared to
Radiance classic is concerned, we had an email trail on this last week
in the Daysim discussion forum
(http://groups.google.com/group/daysim/browse_thread/thread/3029e67b22c2
2a830) .

Best regards,

Christoph

···

From: [email protected]
[mailto:[email protected]] On Behalf Of
Nicolas Roy
Sent: Monday, September 22, 2008 10:04 AM
To: Radiance general discussion
Subject: [Radiance-general] DAYSIM vs. Radiance illuminance values

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

[email protected]

4

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 <[email protected]>
Sent by: [email protected]
22-09-2008 16:40
Please respond to
Radiance general discussion <[email protected]>

To
Radiance general discussion <[email protected]>
cc

Subject
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

···

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general