[Radiance-general] Modelling sky using sky scanner MS-321LR

[Lars O. Grobe]

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Hi Ehsan,
German already gave the answers, I just want to add some.
> 1) what is 10 real arguments in the sky scene generated by gendaylit 
> (below you will find the example)
For a description of the Perez sky model, see page 175 of John's thesis:

http://www.iesd.dmu.ac.uk/~jm/lib/exe/fetch.php?media=resources:mardaljevic_chap5.pdf

The ten arguments are explained in perezlum.cal:

A1 - diffus normalization
9 	A2 - ground brightness
10 	A3,A4,A5,A6,A7 - coefficients for the Perez model
11 	A8,A9,A10 - sun direction


> 2) why when we generate a sky for instance with sun description, we 
> should always include the sky scene as a glowing source otherwise the 
> illuminance values will be zero.
The sky generators in Radiance output modifiers, just as German 
mentioned. This modifiers "scale" the brightness of whatever you apply 
them to.

In most cases, you will scale a glow applied to a hemisphere (modeled as 
a distant source) of brightness 1, as the generator will give you 
brightness in absolute values by default. In this case, the result of 
the generator would directly match the sky brightness in your scene.

However, if you want color, you would first define the brightness of a 
glow material in a way that your normalize the desired color to 1, and 
than apply the modifier to this colored glow material. The modified glow 
material would keep the color you wanted, but scale this according to 
the sky model.

In other cases, if you have no geometry outside the space you are 
interested in, you can even apply the modifier to a glow of uniform 
brightness of one applied to the window-plane.

So there are many ways you can make use of the distribution, and 
including any kind of geometry into the output of the sky generator 
would just limit its applications.

Cheers, Lars.
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