Geocentric Datum of Australia 1994
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The Geocentric Datum of Australia 1994 (GDA94) is a geodetic datum covering the Australian continent. Details of this datum are provided by the GDA94 Technical Manual.[1]
Contents
History
The GDA94 datum was formalized in 1994, replacing the previous datums which were being used in Australia at the time, the Australian Geodetic Datum 1966 (AGD66) and the Australian Geodetic Datum 1984 (AGD84).
Prior to 1966, maps in Australia were produced in miles using the Australian National Grid.[2]
Map Grid of Australia 1994
At the same time as GDA94 was defined, a Universal Transverse Mercator coordinate system called the Map Grid of Australia 1994 (MGA94) was also defined to replace the existing Australian Map Grid (AMG). This new map grid used the GDA94 datum and the GRS80 ellipsoid.
Relation to other datums
For many users, GDA94 can be treated as being the same as the World Geodetic System 1984 (WGS84).. However, where high accuracy is required, one must take into account that GDA94 is a time-dependent datum. GDA94 moves with the Australian continental plate. It was identical to the WGS84 datum in 1994, but since then has drifted at the rate of approximately 6 cm north per year. In 2000, the difference was approximately 45 cm.[3]
Modernisation
The Intergovernmental Committee on Surveying and Mapping (ICSM) has proposed a two stage plan to update the datum, given a working title of GDA2020.[4]
Software for coordinate conversions
- DatumTran: http://www.lpi.nsw.gov.au/surveying/geodesy/gda/datumtran_software
- AusDatumTool: http://www.binaryearth.net/AusDatumTool/index.php
