Geocentric Datum Of Australia (GDA)

The Australian Geodetic Datum was proclaimed in the Australian Commonwealth Gazette of 6 October 1966.  This proclamation included the parameters of the local ellipsoid, known as the Australian National Spheroid (ANS), which defines the adopted size and shape of the earth, and the position of the origin point - Johnston Geodetic Station

JOHNSTON:

Latitude		S 25° 56' 54.551 5"
Longitude		E 133° 12' 30.0771"
Ellipsoidal height	571.2 metres

Australian National Spheroid:

Semi-major axis (a)     6,378,160.0   metres
Semi-minor axis (b)     6,356,774.719 metres
Flattening (f)          1/298.25

The adoption of this origin and best fitting local ellipsoid means that the centre of the ANS does not coincide with the centre of mass of the earth but lies about 200 metres from it.

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