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Old 06-07-2014, 07:55 PM   #27 (permalink)
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MetroMPG had to crank the handle on this page for a whole page before it took off...

EDIT: ideally you would use the sun at sunrise/set, but good luck finding such a wall/unobstructed sightline.
I like this best. A turn-out on Highway 101 at sunset, and a 4x8 sheet of white coroplast (folded in half for transportation). Use an East-West shadow to judge exactly when the light is horizontal. Trace 1/2 on one side and the other on the obverse.

Then fill it in with a Sharpie, photograph it, put it in the GIMP, crop it to a bounding box, blur it to infinity, sample the resulting gray, convert the RGB to a percentage and take that area of the bounding box. Done.
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