> scott <sco### [at] scottcom> wrote:
>>> But I'm wondering: while you cite the Preetham paper you do use
>>> different values for the A to C parameters and also for the Perez
>>> formulation.
>>
>> I took the values that the Stellarium source code used rather than the
>> paper itself, I guess the authors of Stellarium tweaked them a bit. I
>> guess you can use whichever set look better for you.
>>
>>> Also I'm wondering about the multiplication factor of 1000 for the
>>> zenith luminance. As far as I understand it this formula return the
>>> luminance in cd/m2 therefore this additional multiplication just makes
>>> the exposure factor unnecessary small.
>>
>> The formula in the paper gives the luminance in K cd/m2, that's why the
>> 1000 factor is in there.
> 
> Quick question:
> 
> How do I convert the units of ExposureFactor to my scene?
> 
> In my scene, 20 units = 1 foot.
> 
> Thanks!!
> 
> 
> Mike
> 

The formula use meter, a meter = about 39 inches, or 3 feet and 3 inches 
(3.25 feet in 1 m).
There are 10.5625 square feet in a square meter.

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