GDA2020

Implementation status

The Intergovernmental Committee on Surveying and Mapping (ICSM) is leading the national implementation of Geocentric Datum of Australia 2020 (GDA2020). Landgate is coordinating implementation of the new datum in Western Australia.

The agreed date for ANZLIC member agencies in Australian states and territories to be ready to deliver and receive foundation spatial data on the GDA2020 datum was 30 June 2020. Please refer to the ANZLIC GDA2020 adoption date announcement.

Landgate has committed to change its systems and update data to take advantage of the new datum. The implementation will be completed in stages:

  1. In June 2018 as part of GDA2020 implementation project stage 1, Landgate upgraded its geodetic database to provide GDA2020 coordinates and positional uncertainty on all state geodetic Survey Marks.
  2. As of Monday 17 August 2020, the WA Spatial Cadastral Database (SCDB) is being maintained in GDA2020. SmartPlan, CSD Editor and NLR-P systems now allow for cadastral survey data (CSD files) submissions in GDA2020 or GDA94. Updated survey practice guidelines are available on the Land Surveyors Licensing Board website. Landgate encourages surveyors to use GDA2020 for new projects.
  3. Stage 3 of the Landgate GDA2020 implementation project has commenced. This project will run over the 2020/21 financial year and focus on systems delivering data to our customers. Redevelopment of the Shared Location Information Platform data downloads solution will occur, delivering GDA2020 compliant data while continuing legacy support for GDA94.

Geospatial data such as cadastre, imagery, administrative boundaries, road centrelines, topographic, geographic names and more are already available for delivery in GDA2020.  To request Landgate's geospatial data use our land data website or contact our Business and Government Solutions team via phone on +61 (0) 9273 7683 or emailing BusinessSolutions@landgate.wa.gov.au.

If you haven't already, we encourage you to start your own implementation. Most software vendors have now implemented the GDA2020 datum and transformation tools.

GDA2020 queries that are specific to the implementation by Landgate can be directed to the Landgate - GDA Modernisation Implementation Working Group by email positioning@landgate.wa.gov.au.

Legislation

On 11 October 2017, the National Measurement Institute signed off and gazetted GDA2020 as the new Recognized-Value Standard of Measurement of Position as per the Determination 2017.

ANZLIC member agencies in Australian states and territories require changes to their respective regulatory framework documents by 30 June 2020. This is so all states and territories are ready to deliver and receive foundation spatial data on the GDA2020 datum. While each agency is responsible for updating its own legislation, Landgate can provide support. Please contact our Legislation and Policy team for more information (email: LegislationAndPolicy@landgate.wa.gov.au). Refer to the ICSM report for GDA2020 legislation impact assessment and recommendations.

Land Administration Regulations 1998 and Land Information Authority Regulations 2007 were amended to prescribe GDA2020 datum from 1 July 2020.

Technical information

Our team, together with other jurisdictions and Geoscience Australia, developed GDA2020 [EPSG: 1168]. This datum consists of all Landgate’s survey archive data (revised and rescaled as required), as well as the most recent surveys. GDA2020 is free of many of the biases and distortions associated with GDA94 and aligns better to the global reference frame, in which GNSS operate. GDA2020 is a product of a single national network adjustment with rigours error propagation from Continuously Operating Reference Stations (CORS). For more information about GDA2020 refer to ICSM website.

Datum transformation

Coordinate transformation is the process of changing coordinates from one datum (reference frame) to another. There are three options for the transformation of coordinates between GDA94 and GDA2020:

  • 2D conformal NTv2 grid file [EPSG: 8446]
  • 2D conformal + distortion NTv2 grid file [EPSG: 8447]
  • 3D 7-parameter similarity (Helmert) transformation (conformal) [EPSG: 8048]

There are additional 2D conformal only transformation grids for the Indian Ocean Territories:

  • Christmas Island [EPSG: 8444]
  • Cocos (Keeling) Island [EPSG: 8445]

Note: There are no conformal + distortion NTv2 grids available for the Indian Ocean Territories. Below figure shows the extent of the NTv2 national conformal + distortion transformation grid.

GDA94 to GDA2020 transformation grid extent

The following facts should be considered before selection of GDA94-GDA2020 transformation method:

  • If local geodetic network control marks (SSMs) were used for referencing and/or establishing GDA94 coordinates, localised distortion will need to be taken into account. In this case, the conformal + distortion grid should be used to transform the GDA94 coordinates to GDA2020.
  • If GDA94 coordinates were observed using Global Navigation Satellite System (GNSS) technology, with corrections coming from a network of GNSS reference stations (CORS), it is likely that the coordinates will be unaffected by local distortions. In this case, the conformal grid or a seven-parameter similarity transformation would be most suitable to transform the GDA94 coordinates to GDA2020.

Consideration for selection of GDA94 - GDA2020 transformation method

Unless the benefits of adopting another transformation method [EPSG:  8446 or 8048] have been expressly identified, the conformal + distortion NTv2 transformation grid [EPSG: 8447] is the recommended transformation method for spatial data in Western Australia. Use the 7-parameter similarity transformation method or NTv2 conformal only grids to transform data outside the extent of conformal + distortion grid.

For GDA94 to GDA2020 transformation products, tools and manual refer to ICSM website and the Coordinate Transformation section of the GDA2020 Technical Manual.

Important note: Comparing the transformed GDA94 coordinates to the GOLA published GDA2020 coordinates of an SSM is not a valid check for transformation calculations. GOLA coordinates have been determined by a rigorous network adjustment. All transformation methods have a degree of uncertainty, and for example, the conformal + distortion NTv2 transformation grid provides localised (latitude and longitude based) transformation error in the file (attribute three and four). Thus, when comparing transformed GDA94 coordinates to the published GDA2020 coordinates, small differences attributed to the transformation error are expected. Datum transformation should not affect orthometric height (AHD). To test your transformation method we recommend using Geoscience Australia GDA94 - GDA2020 Online Transformation Service. This service provides a reference standard to enables software developers and spatial professionals to transform their data.

Web-mapping applications

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. WGS84 is not the Australian Recognized-Value Standard of Measurement of Position as determined by the National Measurement Institute and it is not prescribed in our legislation. In addition, WGS84 is a time dependant datum (not static) and the Web Mercator is not a conformal projection. Using WGS84WM can yield significant data misalignment and distortion.

The dynamic nature of WGS84 means that it coincided with GDA94 in 1994 and again with GDA2020 in 2020. This creates a well know issue for the web-mapping environment where GDA94 and GDA2020 data are misaligned when using null transformations [EPSG: 1150 and 8450].

We recognise the need to continue to support WGS84WM in web-mapping. To avoid spatial data misalignment in the web mapping environment or when spatial data is provided in a datum nominated as WGS84, this data will be aligned to GDA94 (WGS84 at epoch 1994.0). To publish GDA2020 data in WGS84 based web-mapping environment, this data should first be transformed to GDA94 (see transformation recommendation above), then to WGS84 using null transformation (EPSG: 1150).

The use of WGS84WM for data exchange is discouraged as foundation spatial data must be maintained and distributed in the GDA2020. This is to comply with the National Measurement (Recognized-Value Standard of Measurement of Position) Determination 2017, Landgate's Regulations, and to ensure data quality and integrity is not lost.

Important note: Metrics such as distances, areas or bearings should not be derived from WGS84WM coordinates. Use other conformal (shape-preserving) projections such as UTM or TM (eg. MGA2020 Zone 50, PCG2020).

For additional information related to WGS84WM issue please refer to this ICSM report.

Metadata

GDA2020 differs by only 1.8 m from GDA94, which is why it is extremely important to provide the datum name and, if applicable, transformation method. Refer to the ICSM metadata document for implementation details and examples.

ATRF - Australian Terrestrial Reference Frame

Like GDA94, GDA2020 is fixed to the Australian continent, where coordinates do not change with time. GDA2020 is a static reference frame (static datum). However, on 1 January 2020 ICSM introduced a time dependent reference frame called Australian Terrestrial Reference Frame (ATRF). Coordinates in ATRF will change over time as the Australian continent drifts and due to local deformation. ATRF is a time dependent reference frame (dynamic datum). The first realisation of ATRF is called ATRF2014. For more information refer to ICSM website and ATRF technical implementation plan.

Important note: Both ATRF2014 and GDA2020 will be supported. GDA2020 is available for users who do not need a time-dependent reference frame. ATRF is optional and only for users who do need a time dependant reference frame. GDA2020 and ATRF are compatible and support different user requirements. The Australian Plate Motion Model can be used to propagate coordinates between GDA2020 and ATRF2014.

Modernising Australian Geospatial Reference System

Official forum supports switch to GDA2020

An online forum has been established by the ICSM to share experiences and find answers relating to questions about the modernisation of Australia's datum. It is moderated by members of the GDA Modernisation Implementation Working Group and other technical specialists from around Australia. More about datum modernisation can be found on GDA Modernisation and Implementation Working Group website.

Geodetic news

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Need help?

For more information contact a member of the Survey Services team on +61 (0)8 9273 7111 or email geodesy@landgate.wa.gov.au.

This page was last updated on: 16 Nov 2020