http://en.wikipedia.org/wiki/Georef
http://www.map-reading.com/ch4-4.php

Georef is also assuming whole area on earth as a rectangle in Mercator projection.
First, divide latitude into 12 , and longitude into 24 as following figure.
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Then, divide subsequently into 1 degree by 1 degree area. Then, add ‘minutes” part.

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Sample Code: GJPJ3716

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