GDA2020

Implementation status

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.

ICSM has agreed that 30 June 2020 will be the date when ANZLIC member agencies in Australian states and territories will be ready to deliver and receive foundation spatial data on the GDA2020 datum. Please refer to the ANZLIC GDA2020 adoption date announcement. We encourage you to start your own implementation. Most software vendors have now implemented the GDA2020 datum and transformation tools.

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

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 use our Land Data website or contact our Business & Government Solutions Team on +61 (0) 9273 7683 or email BusinessSolutions@landgate.wa.gov.au.

Landgate’s GDA2020 implementation project Stage 2 is progressing well. SmartPlan and the SCDB are on track to maintain WA cadastre in GDA2020 by 14 of June 2020. The NLR-P system will also be updated to allow for survey data to be submitted in both GDA94 and GDA2020.

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 impacts

On 11 October 2017 National Measurement Institute signed off and gazetted the Geocentric Datum of Australia 2020 (GDA2020) as the new Recognised-Value Standard of Measurement of Position. In effect, GDA2020 is now our new datum and GDA94 has been revoked. Here is a link to the Determination.

ANZLIC member agencies in Australian states and territories require changes to their respective regulatory framework documents by June 30th of 2020. This is so we are all 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).

We have already prepared drafting instructions to conduct our own regulatory change (Land Administration Regulations 1998 and Land Information Authority Regulations 2007) to enable GDA2020. Refer to the ICSM report for GDA2020 legislation impacts and recommendations.

GDA2020 technical information

Our team, together with other jurisdictions and Geoscience Australia, has developed GDA2020 [EPSG: 1168]. This datum consists of all Landgate’s survey archive data (50+ years), as well as modern GNSS survey data (including data donated by your organisation).

Such a large single adjustment has never been done before. It was possibly due to the increased computing power, as well as innovative methods of computing and data analysis. GDA2020 is free of many of the biases and distortions associated with GDA94. It aligns better to the global reference frame, in which GNSS operate. For more information about GDA2020 refer to ICSM website.

GDA94 - GDA2020 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 [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 Western Australia. Use the 7-parameter similarity transformation method or NTv2 conformal only grids to transform data outside the extent of conformal + distortion grid. Horizontal datum transformation should not affect orthometric height (AHD71).

For GDA94 to GDA2020 transformation products and tools refer to ICSM website. Many software vendors have already implemented the GDA94 to GDA2020 transformations and Geoscience Australia also provides a web service that transforms selected spatial formats. For more details refer to the Coordinate Transformation section of the GDA2020 Technical Manual and the ICSM Datum Technical Fact Sheet: TECH Fact sheet 1: GDA94 to GDA2020 transformation.

Important note: All transformation methods have a degree of uncertainty and will introduce errors. For example conformal + distortion NTv2 grid provides localised (latitude and longitude based) transformation error in the GSB file.

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 Recognised-Value Standard of Measurement of Position as determined by National Measurement Institute and it is not prescribed in our legislation. In addition, WGS84 is 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). GDA2020 data published as WGS84 should be transformed first to GDA94 (see transformation recommendation above), then to WGS84 using null transformation (EPSG: 1150).

The use of WGS84WM for data exchange should be discouraged as foundation spatial data must be maintained and distributed in the GDA2020. This is to comply with the current legislation 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).

Metadata

GDA2020 differs by only 1.8 m from GDA94, which is why it is extremely important to provide datum name, and if applicable transformation method. Refer to the ANZLIC endorsed national metadata standard AS/NZS ISO 19115-1:2015 and the associated metadata schema ISO/TS 19115-3:2016 for implementation details.

ATRF - Australian Terrestrial Reference Frame

Like GDA94, GDA2020 is fixed to the Australian continent, where coordinates do not change with time. GDA2020 is static reference frame (static datum). However, on January 1st 2020 ICSM has introduced a time dependent reference frame called Australian Terrestrial Reference Frame or 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 technical implementation plan.

Important note: Both ATRF2014 and GDA2020 will be supported. GDA2020 will be available for users who do not need a time-dependent reference frame. ATRF is optional and only for users who do need time dependant reference frame and is not intended to be mandatory. GDA2020 and ATRF are compatible and to 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: 26 Mar 2020