Gensky question

Hi everyone,

I just have a very quick question.

I am using gensky function to generate a sky distribution with sun, here is
part of the scripts.

void light solar

0

0

3 7.07e+006 7.07e+006 7.07e+006

I just wonder how does Radiance calculate the RGB radiance values of the
sun.

Many thanks,

Jiajie

Hi Jiajie,

You can refer to the source code of GENKY. There you can see the formulas used to calculate RGB from the direct irradiance. Here is the link:

if (u_solar == -1)
  solarbr /= 6e-5*sundir[2];
else if (u_solar == 0) {
  solarbr = 1.5e9/SUNEFFICACY *(1.147 - .147/(sundir[2]>.16?sundir[2]:.16));
if (skytype == S_INTER)
  solarbr *= 0.15; /* fudge factor! */

Cheers,
Ehsan

···

On 10 Aug 2015, at 15:32, Jiajie Zhu <[email protected]> wrote:

Hi everyone,

I just have a very quick question.
I am using gensky function to generate a sky distribution with sun, here is part of the scripts.

void light solar
0
0
3 7.07e+006 7.07e+006 7.07e+006

I just wonder how does Radiance calculate the RGB radiance values of the sun.

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

Hi Jiajie,

gensky calculates the radiance based on the "old" CIE standard skies. It sets all channels RGB to identical values (7.07e006 in your case). In many cases, simulations aim at results over all three channels, which is why most models do not focus on the prediction of color / spectrum. If you really need that, there are sky models aiming at color information, e.g. the Utah model. Mark Stock shared his cal-file to support that model in Radiance:

http://markjstock.org/radiance/

However be aware that we usually rely on information that was measured with sensors not resolving over color channels, so there are a lot of assumptions to generate such colorful sky descriptions.

Cheers, Lars.

···

Hi everyone,

I just have a very quick question.

I am using gensky function to generate a sky distribution with sun, here is part of the scripts.

/void light solar/

/0/

/0/

/3 7.07e+006 7.07e+006 7.07e+006/

I just wonder how does Radiance calculate the RGB radiance values of the sun.

Many thanks,

Jiajie

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