Australian Geodetic Datum
The Australian Geodetic Datum (AGD), both the 1966 and 1984 versions, have been replaced by Geocentric Datum of Australia (GDA94).
Australian Geodetic Datum 1966 (AGD66)The least squares adjustment of the Australian geodetic network performed in March 1966, used the Australian Geodetic Datum. This adjustment produced a set of coordinates which, in the form of latitudes and longitudes, is known as the Australian Geodetic Datum 1966 coordinate set (AGD66).
The grid coordinates derived from a Universal Transverse Mercator projection of the AGD66 coordinates, using the Australian National Spheroid, is now known as the Australian Map Grid 1966 coordinate set (AMG66).
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. This image displays the Johnston Geodetic Station Stone Marker - S 25° 56' 54.5515", E 133° 12' 30.0771", 571.2 metres (ellipsoid height). (Select image to view larger 85k version)
|Semi-major axis (a):||6 378 160.0 metres|
|Semi-minor axis (b):||6 356 774.719 metres|
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.
Extract from: Commonwealth Gazette, No 84, 6th October 1966At the twenty-fourth meeting of the National Mapping Council held in Melbourne, the Council, on 21 April 1966, adopted the following datum for Australian Geodetic Surveys:
Department of National Development
National Mapping Council
- Designation: The Australian Geodetic Datum
- Reference spheroid: The Australian National Spheroid with a major (equatorial) radius of 6 378 160 metres and a flattening of 1/298.25
- Origin: The Johnston Geodetic Station situated in the Northern Territory at East Longitude 133° 12' 30.0771" and South Latitude 25° 56' 54.5515" and with a ground level elevation of 571.2 metres above the spheroid.
Director of National Mapping
Chairman of National Mapping Council
Australian Geodetic Datum 1984 [AGD84]
In 1982, a new national adjustment, referred to as the Geodetic Model of Australia 1982 (GMA82), was performed using all data previously included in the 1966 adjustment as well as additional, modern terrestrial and space-based observations. This new adjustment also used the gazetted Australian Geodetic Datum. The coordinate set resulting from this adjustment was accepted by the National Mapping Council in 1984 and is known as the Australian Geodetic Datum 1984 (AGD84).