The Geocentric Datum of Australia (GDA94) is the official geodetic datum adopted nationally across Australia on 1 January 2000. GDA94 replaced the Australian Geodetic Datum 1966 (AGD66) and Australian Geodetic Datum 1984 (AGD84). The standard map projection associated with GDA94 is the Map Grid of Australia 1994 (MGA94), a transverse Mercator projection that conforms to the internationally accepted Universal Transverse Mercator Grid system.
GDA94 is a coordinate reference system that best fits the shape of the earth as a whole. It has an origin that coincides with the centre of mass of the earth, hence the term ‘geocentric’ GDA94 is a static coordinate datum based on the International Terrestrial Reference Frame 1992 (ITRF92), held at the reference epoch of 1 January 1994.
The GDA94 Gazettal values can be found in the GDA94 Technical Manual v2.4.
Report on background to latest GDA94 modernisation proposal is now available
In February 2015 the PCG proposed a revised Roadmap to modernise the Geocentric Datum of Australia 1994 (GDA94). Stakeholder Requirements for Modernising Australia’s Geocentric Datum describes the information considered by the PCG prior to its determination of the revised proposal.
Prepared by Scott Strong on behalf of the CRC for Spatial Information for ICSM, the report indicates that the availability of ubiquitous accurate GNSS supported positioning is inevitable within Australia, possibly by as early as 2020. Typical of the rate of change that is a characteristic of the mobile digital era, a ‘tsunami’ of adoption is envisaged whereby literally millions of Australians may utilise this positioning technology within several years of its development, as government, industry, science, and consumer users will all equally be able to access decimetre level “globally” accurate locations in real time.
It is widely recognised that GDA94 is not capable of meeting the requirements of a national spatial reference system that supports ubiquitous accurate positioning – it does not support the ability for spatial data sets to be correctly related to GNSS derived globally consistent locations.
Consequently, the national datum must be modernised, and the report makes 17 recommendations for the implementation of a spatial reference framework that will meet all stakeholder requirements, and minimise the disruptive effects associated with the anticipated rate of change associated with technology uptake across the whole Australian community.