[Radiance-general] sky luminance calculation

[Thomas Bleicher]

On 21 Jan 2009, at 11:14, Valeria De Giuli wrote:

> Hi all,
> I have a curiosity about how gensky works. Does anyone know how gensky
> calculate sky luminance values for different latitudes?

Gensky creates CIE sky descriptions. These do not dependent
on the latitude directly, but the sky brightness is defined
via sun angle (zenith) that obviously does depend on the
location.

> For example, where it takes the zenith luminance?

In terms of absolute values there are some hard coded in the
gensky.c source file. However, if you don't specify values
for horizontal or solar radiance (-b/-B or -r/-R) the absolute
value is meaningless.

You can find the sky distribution functions in the file
skybright.cal and a description in various CIE publications.


Regards,
Thomas