[Radiance-general] distribution of short wave radiation with Radiance

[Greg Ward]

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: oga6ya at yahoo.co.jp
> 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
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