distribution of short wave radiation with Radiance

Hi,all

I'm trying to make the distribution of short wave radiation with Radiance.

I used gensky command to make the sky.

The bellow is gensky command I use.

! gensky 1 15 15:0 +i -B 57 -R 455 -a 43.0528 -o -143.2123 -m -150.0

After that, I made hemisphericalimage by -vv 180 -vh 180 in the below command.

rview rvu -vth -vp 0 0 0 -vd -0.546722 -0.779656 0.305337 -vu 0.175306 0.249997 0.952244 -vv 180 -vh 180 -vo 0.0 -va 0.0

Also, I getthe pixel value bypvalue command.

pvalue -h -H -o filename.pic | rcalc -e '$1=$1;$2=$2;$3=$3;$4=$4;$5=$5;$6=$3+$4+$5;$7=$3*47+$4*117+$5*15'>filename.dat

Then I integrated the pixcels of the image to get the direct solar radiation and horizontal solar radiation.

But, Those values are different with the values that I defined on the gensky command-B and -R.

Please advise me something about this.

Regards,

Ogata

It is really very difficult to do what you are attempting without running into multiple errors. For one thing, integrating the sun, which will cover only a few pixels in an image, is problematic. Also, you can neither add together R+G+B nor use the luminance factor 179 (built into your 47, 117, 15 scalars) in your conversion. That said, the following should work for the sky component (-i option):

( oconv - | rpict -vd 0 0 1 -vu 0 1 0 -vth -vh 180 -vv 180 -x 1024 -y 1024 | pvalue -h -H -b -d | total -m | rcalc -e '$1=$1*4' ) << _EOF_

!gensky 1 15 15:00 -i -B 57 -a 43.0528 -o -143.2123 -m -150.0

skyfunc glow skyglow
0
0
4 1 1 1 0

skyglow source sky
0
0
4 0 0 1 180
_EOF_

The final multiplier of 4 is perhaps difficult to understand. Because the image covers a square area, whereas you only want the circle in the center, you need to multiply the average by 4/pi. However, you also need to multiply the averaged result by pi to get irradiance (rather than averaged radiance). Hence, you need to multiply by pi*4/pi, which is just 4. Using this, I get back a value of 56.736 (rather than 57.0), showing the normalization is not perfect.

If I try to compute the output of the sun only, I can do this by leaving off the sky description and going to a much higher resolution image:

gensky 1 15 15:0 +i -R 455 -a 43.0528 -o -143.2123 -m -150.0 \
  > oconv - | rpict -vd 0 0 1 -vu 0 1 0 -vth -vh 180 -vv 180 -x 10000 -y 10000 \
  > pvalue -h -H -b -d | total -m | rcalc -e '$1=$1*4'

The above yields a result of 444.1, which is a higher relative error than the sky calculation most likely due to the difficult of integrating such a small source using a full hemispherical image.

I hope this helps.
-Greg

···

From: [email protected]
Date: October 11, 2012 4:22:36 AM GMT+02:00

Hi,all

I'm trying to make the distribution of short wave radiation with Radiance.

I used gensky command to make the sky.

The bellow is gensky command I use.

! gensky 1 15 15:0 +i -B 57 -R 455 -a 43.0528 -o -143.2123 -m -150.0

After that, I made hemispherical image by -vv 180 -vh 180 in the below command.

rview rvu -vth -vp 0 0 0 -vd -0.546722 -0.779656 0.305337 -vu 0.175306 0.249997 0.952244 -vv 180 -vh 180 -vo 0.0 -va 0.0

Also, I getthe pixel value by pvalue command.

pvalue -h -H -o filename.pic | rcalc -e '$1=$1;$2=$2;$3=$3;$4=$4;$5=$5;$6=$3+$4+$5;$7=$3*47+$4*117+$5*15'>filename.dat

Then I integrated the pixcels of the image to get the direct solar radiation and horizontal solar radiation.

But, Those values are different with the values that I defined on the gensky command -B and -R.

Please advise me something about this.

Regards,
Ogata