GDA2020 Background
On the 11th of October, 2017, GDA2020 was defined by determination under Commonwealth legislation as the Recognised Value-Standard of Measurement of Position for Australia. GDA2020 replaced the Geocentric Datum of Australia 1994 (GDA94). The determination was made by the Chief Metrologist of the National Measurement Institute, under the National Measurement Act 1960.
https://www.legislation.gov.au/details/F2017L01352
Even though GDA2020 is the Recognised Value Standard of Measurement of Position for Australia, it has been left to each jurisdiction to decide on the timing and manner of implementation. Currently, the Northern Territory Government still requires all submissions to be in GDA94, unless specified otherwise. The geospatial and broader community will be given advance notice of any changes in submission requirements to allow adequate preparation for the change.
Accessing GDA2020
On the weekend of the 9th and 10th of February, 2019, the AUSCORS network implemented GDA2020. AUSCORS is the network of global navigation satellite systems (GNSS) continuously operating reference stations (CORS) that are run by Geoscience Australia and spread across the country. The AUSCORS network in the Northern Territory can be used for Network Real Time Kinematic (RTK) and as a single base mount point. The implementation of GDA2020 involved the following:
- The configuration of GDA2020 as the default datum.
- The configuration of all AUSCORS receivers with GDA2020 Regulation 13 coordinates.
- Providing mount points for both GDA2020 and GDA94.
This allows users of the AUSCORS network to select which datum they wish to work in when accessing the network. For users of commercial CORS providers, such as SmartNet, it is recommended to contact your provider for their current status.
AHD and GNSS
GDA2020 and GDA94 are both horizontal datums. The Australian vertical datum is still the Australian Height Datum 1971 (AHD). Geoscience Australia provides geoid models that convert the ellipsoid heights provided by GNSS to AHD heights. Users must use the correct geoid model for the datum that they are working in in order to get the best estimates of AHD with GNSS. These are AUSGeoid2020 for GDA2020 and AUSGeoid09 for GDA94.
Transformation of Coordinates
The tools to transform between GDA94 and GDA2020 have been incorporated into many commercial software packages. Please contact your software vendor if your software of choice does not yet provide support for GDA2020. A range of free tools have also been developed for coordinate transformation.
An online transformation service is available at http://positioning.fsdf.org.au/. It accepts a variety of file formats and can transform single and multiple points.
Metadata
An important aspect of working with geospatial data is ensuring that the metadata is correct. Good metadata has enough information to be of use both now and into the future. The epoch, time of data collection, should be noted as well as the datum. Having the epoch in the metadata will allow for more accurate transformations. It will also ensure that layers of geospatial data will remain aligned over time.
Other Resources
The ICSM has section of its website devoted to datum.
https://www.icsm.gov.au/what-we-do/geocentric-datum-australia.
This site is the authoritative source on matters datum. Here you will find background on the datum change, the GDA2020 and GDA94 technical manuals, links to transformation tools and products, fact sheets, and more.
Geoscience Australia’s Positioning and Navigation web portal provides information and tools on many positioning and geodetic topics.
http://www.ga.gov.au/scientific-topics/positioning-navigation
Some of the topics include:
AHD and Geoid Models
http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/ahdgm