This article was originally published on 19 Mar 2020 by The Data WA Team
GDA2020 Implementation Progress
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 Intergovernmental Committee on Surveying and Mapping (ICSM) is leading the national implementation of GDA2020 and Landgate is coordinating implementation of the new datum in Western Australia.
Landgate GDA2020 implementation project update
As part of GDA2020 implementation project Stage 1 Landgate has upgraded its geodetic database to provide GDA2020 coordinates and positional uncertainty on all State geodetic Survey Marks.
Stage 2 is progressing well with SmartPlan and the SCDB on track to be upgraded to maintain WA cadastre in GDA2020 by 14 June 2020. The NLR-P system will also be updated to allow for survey data to be submitted in both GDA94 and GDA2020.
Geospatial data such as cadastre, imagery, administrative boundaries, road centrelines, topographic, geographic names and more are also available for delivery in GDA2020. To request Landgate's geospatial data visit our Land data webpage.
Spatial data transformation and support of web-mapping services
Unless the benefits of adopting another transformation method [e.g. EPSG: 8446] have been expressly identified, the conformal + distortion NTv2 transformation grid [EPSG: 8447] is the recommended transformation method for spatial data in WA.
Use the 7-parameter similarity transformation method or NTv2 conformal only grids to transform data outside the conformal + distortion grid. Horizontal datum transformation should not affect orthometric height (AHD71). For more details regarding transformation please refer to the Landgate website.
Current web-mapping services use WGS84 Web Mercator (WGS84WM) Coordinate Reference System (CRS - datum and projection) registered under EPSG: 3857. WGS84 has been popularised as a de facto web-mapping standard by commercial providers and many online maps default to this CRS. However, WGS84 is not the Australian Recognised-Value Standard of Measurement of Position as determined by the National Measurement Institute, nor is it prescribed in our legislation. Furthermore, WGS84 is a time dependant datum (not static), and the Web Mercator is not a conformal projection. This can yield significant data misalignment and distortions.
The dynamic nature of WGS84 means that it coincided with GDA94 in 1994 and again with GDA2020 in 2020. This creates a well-known issue for the web-mapping environment where GDA94 and GDA2020 data are misaligned when using null transformations [EPSG: 1150 and 8450].
© This copyright work is licensed under a Creative Commons Australia Attribution 4.0 licence Author: NSW Government DCS Spatial Services
GDA94 and GDA2020, when displayed together using the de facto -standard ‘WGS84 Web Mercator’ projection can be misaligned by 1.8 metres. This affects all web-mapping software.
The national GDA Modernisation Implementation Working Group (GMIWG) continue to progress the development of new EPSG codes addressing the null transformation issues with EPSG, however the timing of an outcome is unknown.
WA Shared Location Information Platform (SLIP)
Changes to the SLIP data upload tool (DUT) have been completed and custodians can now provide data in GDA2020.
Until web-mapping services adopt more suitable CRS, SLIP will continue to support WGS84WM in web-mapping. To avoid spatial data misalignment in the web-mapping environment, GDA2020 data published as WGS84WM (EPSG: 3857), will be transformed first to GDA94 as per the recommendation in the Spatial data transformation and support of web-mapping services section above, then to WGS84 using null transformation (EPSG: 1150).
Some GIS software such as Esri ArcMap 10.6 and above is already supporting this transformation (e.g. Esri Map Services). Additional server-side CRS support for OGC web services is being planned to assist transformation from WGS84WM to GDA2020 where software does not yet support concatenated transformation via GDA94.
Please check with your software provider to confirm supported transformations and/or align your custom transformations with the above recommendation.
Included in the 2020-21 business case for Landgate’s GDA2020 implementation project Stage 3 is a strategy and technical approach to support the implementation of GDA2020 for SLIP data services. The project aims to upgrade SLIP data downloads to provide spatial data in GDA2020 while continuing to support GDA94. The proposed strategy also aims to support SLIP customers’ needs and plans for GDA2020 implementation and communicate any changes accordingly.
Data.wa.gov.au and metadata
Metadata is extremely important! GDA2020 differs by only 1.8m from GDA94. Without proper metadata this may lead to costly mistakes. Always provide a datum and if applicable transformation method with your spatial data. Metadata should be provided via data.wa.gov.au.
We hope this information is helpful and we encourage you to start your own GDA2020 implementation. For more information and to stay up to date with Landgate's GDA2020 implementation please see Landgate's dedicated GDA2020 page.