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

[Ehsan M.Vazifeh]

Dear Lars and German,

It was a really a comprehensive explanation. I was always concerned about
sky model why its like that. Thank you for the quite useful and important
information you gave to me.

Cheers,
Ehsan


On Tue, Apr 8, 2014 at 11:56 AM, Lars O. Grobe <grobe at gmx.net> wrote:

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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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