“The only thing that remains constant is change!” Nothing on the Earth is static due to continental drift.
Australia moves particularly fast by geological standards, caused by the shifting tectonic plates. According to the New York Times reports, Australia drifts 7 cm north every year, with a clockwise rotation. As Australia has moved 1.8 metres to the northeast over the past 26 years, so how has global positioning systems (GPS) kept up with it?
Every country has its own Geodetic Datum for locating places on the Earth. The one Australia used from the early 1990s is called the Geocentric Datum of Australia 1994 (GDA94). GDA94 “moved” with the drift of the Australian continent, like a giant net tied to the landscape. Based on GDA94, the fixed features on our maps, such as roads, buildings and moving vehicles, thus had unchanging three-dimensional coordinates.
However, we now increasingly rely on use a different datum (global navigation satellite systems GNSS) that is not fixed to any continent, but the centre of Earth, to determine coordinates, such as the European Union’s Galileo and China’s BeiDou.
The global GNSS coordinates and the Australian GDA94 coordinates are getting further out of alignment every year, as Australian is always drifting. We can imagine the mass if a full self-driving Tesla determine its destination using GNSS, but the features were referenced to GDA94, and the location would be nearly two metres away!
So Australia’s Geodetic Datum needs a revision to ensure Australia’s plate-fixed maps are in sync with devices with accurate positioning capabilities. The new continent-fixed datum GDA2020 will bring the coordinates of Australia’s mapped features back into line with global systems for the year 2020! On average it shifts all coordinates in Australia by 1.8 metres to the northeast.
The standard map projection associated with GDA2020 is the Map Grid of Australia 2020 (MGA2020), a transverse Mercator projection that conforms to the internationally standardised Universal Transverse Mercator Grid system. GDA2020 coordinates can be accessed via:
- Commonwealth, state and territory geodetic and survey databases
- GNSS CORS stations with Regulation 13 Certification issued by Geoscience Australia
- Government (https://www.auscors.ga.gov.au/) or commercial real-time services, or
- via transformation of GDA94 to GDA2020 coordinates using the transformation products and tools published by ICSM.