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31 July 2014
Redfearn's Formula, Grid to Geographic
Given Easting, Northing and Zone for a Universal Transverse Mercator (UTM) projection, calculate Latitude, Longitude, Grid convergence and Point Scale Factor.
The calculations are performed using the GRS80 ellipsoid which is used for Australia's new coordinate system (the Geocentric Datum of Australia - GDA) and is also compatible with the global coordinate system (WGS84) (a = 6,378,137.0 metres; 1/f = 298.25722210)
Redfearn's formulae are used (Redfearn, Empire Survey Review, No. 69, 1948) to convert between Latitude & Longitude and easting, northing & zone for a UTM projection, such as the Map Grid of Australia (MGA). These formulae are accurate to better than 1 mm in any zone.