Geocentric Datum Of Australia (GDA)
Background
Reference
ICSM Decision Process
Up until the implementation of the Geocentric Datum of Australia (GDA), the coordinates being used over mainland and offshore Australia included: Pre-1966(Clarke), AGD66, AGD84, WGS72 and WGS84. However, most spatial data in Australia is referenced to the Australian National Spheroid(ANS), which is oriented by one of the two versions of the Australian Geodetic Datum (AGD66 or AGD84). This combination of spheroid and datum were chosen to provide optimal referencing conditions for spatial data across the Australian continent. The ANS is, however, a rather poor reference system over other parts of the world.
The continuing development of global communication, transport and information technologies makes the emergence of a global spatial data infrastructure inevitable. By introducing a geocentric datum, Australia is not only moving towards its own national spatial data infrastructure, but also closer to a global infrastructure. This will ensure compatibility across various geographic information systems at the local, regional, national and global level. There is International support to move to a geocentric datum. Many countries in Europe, North America and the Asia-Pacific region are already developing national spatial data infrastructures within a global context. Australia's move to a geocentric datum will enable us to participate fully in that initiative.
In recent times a geocentric spheroid and datum called the World Geodetic System (WGS84), has gained worldwide support for referencing spatial data, and especially GPS measurements. In Australia, a new spheroidal system has been developed, employing the geocentric GRS80 spheroid, which for all practical purposes is identical to WGS84.
In 1988 the Intergovernmental Committee on Surveying and Mapping (ICSM) decided that Australia would move to the earth-centred coordinate system, GDA. This coordinate system is based on the International Terrestrial Reference Frame (ITRF) recommended by the International Association of Geodesy (IAG). The GDA is based on the Australian Fiducial Network (AFN) which fits into the ITRF. The AFN was used as the foundation to determine geocentric coordinates for the Australian National Network (ANN). The AFN and ANN are the basis of a unique national geocentric coordinate system, which, with regional networks, provide the fundamental framework for all geographic information over Australia.
The implementation of GDA Australia wide is a positive step towards consistency of datum between the many data themes. This important step also has vast economic and practical benefits for Australia. With a geocentric datum as Australia's geodetic reference system, an integrated national geographic data infrastructure can be established. This national resource will support economic, social and environmental decision-making.
In 1990, the International Federation of Surveyors recommended that its members promote and support the adoption of a global geocentric reference system proposed by the International Association of Geodesy. In 1991, the 56 member maritime nations of the International Hydrographic Organisation (IHO), recommended the production of future navigational charts on a geocentric datum. In May 1994 at the UN Regional Cartographic Conference for Asia and the Pacific, all member countries resolved to adopt a geocentric datum as soon as possible. On 6 September 1995, the new geocentric datum was Gazetted. The International Civil Aviation Authority (ICAO) has decreed that WGS84 will be used for its activities, commencing 1 January 1998.
As Australia is an active IHO member, the Navy's Hydrographic Service is producing navigation charts and digital products on a geocentric datum. The Australian Department of Defence is also producing geographic information on a compatible datum. The use of a geocentric datum will facilitate reliable joint operations between allied forces such as the USA, the UK, New Zealand and Canada.
The responsibility to coordinate the implementation of GDA lies with ICSM. This Committee comprises Commonwealth, State and Territory agencies in Australia and New Zealand responsible for surveying and mapping to meet civilian and military needs.
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