The Geocentric Datum of Australia 2020 (GDA2020) is Australia's new national datum. This update to Australia’s national datum has been made in response to advances in technology and will ensure that all Australians enjoy the benefits of accurate positioning in the future.
The Shared Location Information Platform (SLIP) is a multiagency spatial platform hosted in Amazon Web Services (AWS) and managed by the Western Australian Land Information Authority—Landgate—on behalf of the State of WA.
Data is contributed to SLIP from over 25 agencies who are responsible for authoritative spatial data in Western Australia. Each data custodian contributes their data to SLIP and maintains data currency using the SLIP Data Upload Tool (DUT).
Info: SLIP is now prepared to received data in GDA2020 from data custodians. We have also implemented updates to our Data Upload Tool (DUT) to capture extra metadata such as upload datum. This will enable SLIP to retain original data and metadata before any transformations are applied to store and publish data to web services.
Reference: It is best practice for metadata to include information about the underlying datum of spatial data. Data Custodians should refer to the ANZLIC guidelines on preparing metadata for GDA2020 and AGRS.
SLIP Web Services (APIs)
Info: Where SLIP provides data and web services in WGS84, these will be provided in WGS84@1994.0 (the nominal equivalent of GDA94) unless otherwise indicated, to align with existing cached GDA94 data.
Tip: Other WA agencies are recommended to adopt the above principle, or at very least clearly communicate the ‘Coordinate Epoch’ associated with all WGS84 datasets.
GDA94 and GDA2020 are misaligned when projected into WGS84. WGS84 is a dynamic datum—GDA94 and GDA2020 are static datums. GDA94 and GDA2020 data, when displayed together using WGS84 Web Mercator (WGS94 WM), can be misaligned by 1.8 metres.
© This copyright work is licensed under a Creative Commons Australia Attribution 4.0 licence Author: NSW Government DCS Spatial Services
This affects all web-mapping software and has been recognised as an international problem. To avoid metre-level misalignments until web-mapping standards (EPSG registry and ISO standards) are updated it is necessary to choose an appropriate static datum and/or epoch for web-mapping.
SLIP web services will remain in WGS84 (equivalent to GDA94) to support web mapping and avoid data misalignments. The geometry of data supplied to SLIP is transformed to WGS84 (equivalent to GDA94) for storing and publishing, however, any coordinates present in data attributes are not transformed.
Tip: Users should refer to Data WA and the 'Geospatial source projection' to confirm the datum of coordinate attributes in SLIP web services.
Info: Additional datum information has been added to the SLIP Data Update API.
Reference: For advice on web mapping and the use of WGS84 WM please see the ICSM website and GMIWG Advisory on WGS84 and Web Mapping.
Info: Geospatial snapshots (Data Downloads) are currently published in the default storage datum of WGS84.
A new SLIP data download solution is being designed to provide geospatial data snapshots as GDA2020 in June 2021. The new solution will replace service Map Packages with a File Geodatabase (FGDB) for each individual dataset, provide legacy support for GDA94, and the option to choose file format and datum.
Reference: For GDA94 to GDA2020 transformation products, tools and manual refer to ICSM website and the Coordinate Transformation section of the GDA2020 Technical Manual.
GDA2020 Implementation Progress Updates
- Data WA Blog: GDA2020 February 2021 Update
- Data WA Blog: GDA2020 October 2020 Update
- Data WA Blog: GDA2020 Implementation