Australia is moving towards a new coordinate system, Geocentric Datum of Australia 2020 (GDA2020), to facilitate a more robust, accurate, and capable datum which is more closely aligned to global positioning systems like GNSS. This will ensure that Australian industry, the research community, and the public can accurately align themselves and their data. The new GDA2020 datum has been launched by Geoscience Australia and the Intergovernmental Committee on Survey and Mapping (ICSM) on the 15th of December, 2017. The current existing national geodetic datum, Geocentric Datum of Australia 1994 (GDA94), is not capable of meeting the expectations of a modern technical GPS connected Australia. The Australian Government has committed $225 million to provide 5-10 centimeter accurate positioning and it is a significant improvement from the 5-10 meter accuracy currently achievable using GPS enabled devices.
The introduction of GDA2020 has brought additional requirements and considerations for both software providers and users. Esri and Esri Australia have been working closely with ICSM and Geoscience Australia to ensure that ArcGIS software products support the new definitions. With the delivery of ArcGIS Pro 2.2 and ArcGIS 10.6.1, Esri now fully supports GDA2020 and the GDA2020 National Transformation version 2 (NTv2) transformation grid files out of the box.
The introduction of a new coordinate system impacts all areas of the software. The Esri support for GDA2020 was progressively added as the coordinate system and associated transformation methods were released.
Note: GDA2020 is not supported in earlier versions of ArcGIS with the exception of the ArcGIS 10.2.1 utility version.
A geographic transformation is a mathematical operation that converts the coordinates of a point in one geographic coordinate system to the coordinates of the same point in another geographic coordinate system. A grid-based transformation method can be very accurate in modeling small changes between two geographic coordinate systems. Grid files can be reasonably large. The ICSM released two 2D national transformation grids as follows:
Due to the size of these grids, they are available as a separate installation through My Esri for ArcGIS 10.6.1 and ArcGIS Pro 2.2. They are also available directly from the ICSM GitHub site.
There are three available transformation methods between GDA1994 and GDA2020 when working with a supported release and the NTv2 transformation grids have been applied:
As the software is not delivered with grid files, only the seven parameter similarity transformation will appear in ArcGIS until the grid files are loaded into the product directories. Users must ensure that an appropriate transformation method is applied to the map or data frame when displaying GDA94 data in a GDA2020 data frame or vice versa. The geographic coordinate system transformation methods are shown in the images below:
Web GIS by default displays data in WGS 1984 Web Mercator (Auxiliary Sphere) with data often re-projected on the fly to the web projection to align with the basemap and fit the global projection. GDA94 and WGS84 are generally interchangeable with little effect on positional accuracy. Unfortunately, with the modernization of the Australian datum to GDA2020, there is not a definitive relationship between GDA2020 and WGS84. This results in any transformation between GDA2020 and WGS84 having an error of 3 meters or greater.
Data in the web map environment can be displayed against Esri basemaps and web scenes and other WGS84-based data. In most instances, this will not be an issue as the generic basemap data is derived from many sources with varying positional accuracies.
From a user data perspective, Esri Australia recommends the following: