NSW GDA2020 and AGRS Implementation Policy

December 2019

December 2019

NSW GDA2020 and AGRS Implementation Policy

Date: Friday 6 December 2019

Contact details

Digital NSW & Customer Service ICT

Spatial Services

GDA2020 Implementation Program Manager (NSW)

Email: GDA2020@customerservice.nsw.gov.au

NSW GDA2020 and AGRS Implementation Policy | December 2019 1

Table of contents

1. Document control 2

1.1 Document history 2

1.2 Document approval 2

2. Policy context 3

2.1 Authority 3

2.2 Scope 4

3. Policy components 5

3.1 Key accountabilities and responsibilities 5

3.1.1 PMO 5

3.1.2 ICT 5

3.1.3 Office of the Surveyor-General 5

3.2 Communication and consultation 5

3.3 Monitoring and review 5

4. Background 6

4.1 Datum modernisation initiative 6

4.2 Time dependence: Adoption of ATRF 6

4.3 Time-dependence: WGS84 / Web Mercator misalignment problems 7

5. Policy statements 8

6. Further information 9

7. Glossary of terms 10

8. Related policies and documents 14

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1. Document control

1.1 Document history

Version Issue Date Author Reason for Change

0.1 13/08/2019 Marc Strong Joel Haasdyk Draft

0.2-0.9 13/08/2019 – 04/11/2019

Marc Strong Cameron Shorter Joel Haasdyk

Incorporate Feedback, Revise WGS84 policy statements

1.0 12/11/2019 Joel Haasdyk SS feedback/timing include AGRS components

2.0 06/12/2019 Joel Haasdyk SS feedback / Communications feedback.

1.2 Document approval

Name Position Role Date Signature

Joel Haasdyk GDA2020 Program Manager

Approver 6 December 2019

Narelle Underwood

Surveyor-General of NSW

Approver 6 December 2019

Lars Hansen Director, Information Services

Approver 6 December 2019

Tony Hope Manager, Business Technology Services

Reviewer

Shem Semple Manager, Strategy & Architecture

Reviewer

Natasha Steele Manager, Information Management and Security

Reviewer

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2. Policy context

The purpose of this document is to describe how the Department of Customer Service (DCS) Spatial Services will address the management of GDA94, GDA2020 and WGS84 in NSW, as it implements Australia’s datum modernisation program.

The objective is to facilitate the adoption of GDA2020 by current and future NSW geospatial consumers, by ensuring that timelines for introduction and support of the above datums, by DCS Spatial Services, are clear to all users.

This policy also describes a nationally consistent and agreed best practice approach to support the use of WGS84/Web Mercator, acknowledging the potential for misalignment resulting from the NULL GDA94 <> WGS84 and GDA2020 <> WGS84 transformations. (Refer to Section 4.3 for more information.)

2.1 Authority

This policy draws its authority from the Australia and New Zealand Spatial Information Council (ANZLIC) and the NSW Standard for Spatially Enabling Information (SSEI). The SSEI is released by the NSW ICT and Digital Leadership Group (IDLG) in accordance with the NSW Government ICT Strategy.

This standard forms part of the NSW Government Information Management Framework. It also supports several key initiatives at the national, state and agency levels of government. Aligned initiatives and priorities are detailed in the following:

• The Australian and New Zealand Foundation Spatial Data Framework1 • NSW Foundation Spatial Data Framework2 • NSW ICT Strategy3 • NSW Location Intelligence Strategy4

The NSW SSEI Standard defines Coordinates as one of the four core spatial indexes. It identifies the Geocentric Datum of Australia (GDA) as the reference datum for consistent and common referencing of spatial data across NSW. The SSEI currently refers to GDA94 and will shortly be updated to support GDA2020. This reflects changes in the Surveying and Spatial Information (S&SI) Act (2002) and Regulation (2017) which define the prescribed datum for use in NSW.

1 https://www.anzlic.gov.au/resources/foundation-spatial-data-framework 2 https://data.nsw.gov.au/data/dataset/nsw-foundation-spatial-data-framework/resource/010f8c31-770b-42bc-898d-a45897814002 3 https://www.finance.nsw.gov.au/nsw-government-ict-strategy 4 https://www.finance.nsw.gov.au/location-intelligence-strategy

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2.2 Scope

This policy applies to the management and provision of all DCS Spatial Services datasets and services to NSW stakeholders. External agencies, such as other NSW Government Departments or Private Stakeholders, are encouraged to adopt a policy for GDA2020 implementation which is informed by and consistent with this policy.

It is recognised that the Intergovernmental Committee on Surveying and Mapping (ICSM) will continue to expand the definition and capabilities of the Australian Geospatial Reference System (AGRS; https://www.icsm.gov.au/upgrades-australian-geospatial-reference-system). The new time-dependent Australian Terrestrial Reference Frame (ATRF) and the Australian Vertical Working Surface (AVWS) will also be introduced by ICSM and “made available for use from 1 January 2020”.

In general, GDA2020 and AHD71 will remain fit for purpose for most users. Until relevant standards and software provide wide-spread support for ATRF and AVWS, DCS Spatial Services will not advocate or legislate their adoption. However, where significant benefits can be realised, ad hoc support for all AGRS capabilities will be considered.

The policies in this document are formulated to support the immediate adoption of GDA2020 across all stakeholders, and to be consistent with the longer-term adoption of ATRF and AVWS.

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3. Policy components

3.1 Key accountabilities and responsibilities

Each of the following parties has specific assigned responsibilities under this policy.

3.1.1 PMO

Ensure that all new and inflight projects that deliver or maintain spatial datasets beyond January 2020 comply with the GDA2020 implementation policies.

3.1.2 ICT

Ensure that data delivery channels are upgraded to support implementation of the policy.

3.1.3 Office of the Surveyor-General

Undertake internal project audit and provide internal and external advisory services relating to best practice for GDA2020 implementation and addressing the WGS84 problem.

3.2 Communication and consultation

This policy has been developed in collaboration with industry stakeholders in NSW and with other Australian jurisdictions to ensure that a consistent and/or compatible national approach is adopted to support the management of GDA94, GDA2020 and WGS84.

Communication of this policy and related contents will occur through the ‘NSW Datum Modernisation Working Group’ to other government, industry and education representatives, and through the DCS Spatial Services web site.

3.3 Monitoring and review

This policy will be reviewed in July 2020.

Should a national policy on GDA94 / GDA2020 / WGS84 become available, this policy will be reviewed to ensure consistency across Australian jurisdictions.

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4. Background

4.1 Datum modernisation initiative

The Geocentric Datum of Australia 2020 (GDA2020) is Australia’s new National Datum, defined via a National Measurement Determination in October 2017 to replace GDA94. GDA2020 is of higher accuracy than GDA94, aligns more closely with GPS and GNSS positioning services and supports nationally consistent datasets, free of the known distortions of GDA94. GDA2020 coordinates are approximately 1.5 metres to the north east of GDA94 coordinates (in NSW), a change which represents the tectonic motion of the Australian tectonic plate between 1994 and 2020.

GDA2020 is the first product of the modernised Australian Geospatial Reference System (AGRS) which provides the framework for coordinating all spatial information in Australia. These changes are needed to ensure that all users have access to accurate and nationally consistent spatial data and services, to support the economically significant increase in high-accuracy positioning services anticipated over the coming decade. (See AGRS for more details, as well as economic reports: CRSCI, 2008; CRCSI, 2017; FrontierSI, 2019).

ANZLIC has nominated 30 June 2020 as “the date by which all ANZLIC member agencies in Australian states and territories will be ready to deliver and receive foundation spatial data on the GDA2020 datum”. DCS Spatial Services intends to deliver and receive NSW FDSF datasets (e.g. Digital Cadastre, Topography, Addressing, etc.) in both GDA94 and GDA2020, in line with this date.

4.2 Time dependence: Adoption of ATRF

While GDA2020 is a static datum which behaves just like GDA94 (albeit ~1.5m to the NE in NSW), updates to the AGRS will also include the dynamic (or “time-dependent”) Australian Terrestrial Reference Frame (ATRF). ATRF includes the 7cm / year plate motion model needed to properly combine centimetre-level data observed at different epochs, in the light of metre-level movements of the Australian plate.

For many applications, adoption of ATRF and time-dependence is not required for several years into the future and may not require explicit user action. It is expected that many users will gather data directly in GDA2020 (e.g. via a local CORS network) or will require software to bring data together seamlessly at a common epoch.

The international community is aware of the importance of recording, applying and communicating the time stamp(s) associated with data (see e.g. ISO19111). Standards and software are currently under development to address these issues and should allow for as much automation as possible to minimise the need for extensive user education.

Best practice now and in future requires that all spatial metadata record the ‘Observation Epoch’ (time at which the data was observed or measured), and the ‘Coordinate Epoch’ (the time at which coordinates in a dynamic coordinate reference system are referenced).

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4.3 Time-dependence: WGS84 / Web Mercator misalignment problems

It is important to note that WGS84, and the related Web Mercator projection, which are widely applied in web-mapping and web-services, are already time-dependent despite being commonly treated as a static datum/projection.

WGS84 data should always include a timestamp for any data at metre-level accuracy or better, but this metadata is rarely provided. This practice has resulted from:

(1) the origins of WGS84 as the reference system for GPS, which historically provides position information with metre-level (or worse) accuracy (for civilian users), usually intended for near-real time capture and application.

(2) the historic application(s) of web-mapping for low accuracy (i.e. metre-level or worse) spatial data display, where plate tectonic motion can generally be ignored.

(3) the practice of equating WGS84 with a single national datum, resulting in an implicit timestamp being adopted. In practice in Australia, WGS84 has been taken to be equivalent to GDA94, at epoch 1994.0. Note that this implicit epoch is regionally specific, and differs between Australia, Europe, North America, etc.

The failure to account for this issue has resulted in observed misalignments in data when attempting to combine GDA94 and GDA2020 data in WGS84 web-mapping applications.

DCS Spatial Services will provide WGS84 as WGS84@1994.0 (equivalent to GDA94) unless otherwise indicated. It is strongly recommended that users take care when combining different WGS84 datasets without an explicit Coordinate Epoch indicated.

It is recommended that other NSW agencies adopt the above principle to adopt WGS84@1994.0, or at very least a “Truth in Labelling” policy to clearly communicate the Coordinate Epoch associated with WGS84.

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5. Policy statements

For this policy, GDA94 and GDA2020 are taken to mean the Geocentric Datum of Australia 1994 and Geocentric Datum of Australia 2020 respectively, and include where appropriate, data expressed in the related Map Grid of Australia (MGA94 or MGA2020).

1. By 30 June 2020, DCS Spatial Services will provide (and accept) all Foundation Spatial Data in GDA2020.

2. Until 30 June 2023, DCS Spatial Services will also provide (and accept) all Foundation Spatial Data in GDA94.

3. By 1 July 2021, DCS Spatial Services spatial data maintenance environments and workflows will be migrated to work natively in GDA2020.

4. Where transformation of spatial data in NSW is required between GDA94 and GDA2020, the ‘Conformal and Distortion’ NTv2 transformation grid5 is to be used, unless the benefits of adopting another transformation method have been expressly identified.

5. Where data has been transformed, the chosen transformation method is to be clearly communicated in associated metadata.

6. DCS Spatial Services web-services will support data requests for at least the GDA94, GDA2020 and WGS84 Coordinate Reference Systems (CRS), and will return coordinate geometry aligned with the requested CRS.6

7. Where DCS Spatial Services delivers web-services or spatial data in a datum nominated as WGS84, this data will be aligned with GDA94, i.e. expressed in epoch 1994.0.6

8. The Australian Height Datum (AHD71) will continue as the legislated height datum in NSW for the foreseeable future. This is consistent with reported intentions across Australia.

9. DCS Spatial Services expect to support ATRF and AVWS at a future date (yet to be determined) when standards and software to allow the proper treatment of time-dependence in data and transformations are more mature. However, where significant benefits can be realised, ad hoc support for all AGRS capabilities will be considered.

5 GDA94 to GDA2020 NTv2 Conformal and Distortion transformation (EPSG::8447), with accuracy of 0.05 metres. Available as .GSB file from http://www.icsm.gov.au/datum/gda-transformation-products-and-tools/transformation-grids 6 GDA94 data published as WGS84 shall be transformed via null transformation (EPSG::1150) (and vice versa) GDA2020 data published as WGS84 shall be transformed first to GDA94 (per Policy 4), then to WGS84 (EPSG::1150) (and vice versa). This avoids use of the GDA2020 ⇔ WGS84 NULL transformation (EPSG::8450) and aligns WGS84 data with GDA94 (at epoch 1994.0), to avoid potential misalignments when mixing data from different sources. Note: WGS84 is not inherently equivalent to GDA94 in all datasets and applications. Data custodians should review data sources and select an appropriate transformation from WGS84 to GDA94 (or GDA2020) before supplying to DCS Spatial Services. Data consumers should be aware of potential misalignments when using WGS84 and report anomalies. Note: Standards and software are under development to allowing the proper treatment of time-dependence across CRS.

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6. Further information

For questions and further information, please contact:

GDA2020 Implementation Program Manager (NSW) Office of the Surveyor-General Email: GDA2020@customerservice.nsw.gov.au

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7. Glossary of terms

Term Acronym Definition

Australian Height Datum 1971

AHD71 Australian Height Datum 1971 establishes the height reference in Australia, nominally representing height above mean sea level.

The [Australia and New Zealand] Spatial Information Council

ANZLIC The Spatial Information Council (ANZLIC) is a joint initiative of the Australian and New Zealand Governments, and the State and Territory Governments of Australia. ANZLIC is the peak Government body in Australia and New Zealand with the core responsibility for the stewardship of spatial information.

Australian Geospatial Reference System

AGRS The collection of Australian horizontal and vertical reference frames and the model(s) required to transform between them.

Australian Terrestrial Reference Frame

ATRF A regional densification of the International Terrestrial Reference Frame. ATRF is a time-dependent reference frame, defined from several hundred permanent CORS on the Australian mainland and external territories. ATRF is equivalent to GDA2020 at 01/01/2020 and changes over time according to the Australian Plate Motion Model. The extent of ATRF is the same as GDA2020.

Australian Vertical Working Surface

AVWS A new reference surface for height in Australia, free of the bias and distortion known in AHD; A nationally consistent model to transform heights from GNSS ellipsoidal heights to physical heights (i.e. indicating water flow) with sub-decimetre accuracy over large regions.

Coordinate Epoch

The date/time at which coordinates in a dynamic coordinate reference system are referenced (ISO19111) This is usually provided as a decimal year (YYYY.yy).

Coordinate Reference System

CRS A coordinate reference system that is related to an object or objects by a datum. A CRS is typically referenced in Web Service calls by an EPSG code.

Department of Customer Service (NSW)

DCS NSW Government agency responsible for the maintenance and distribution of Foundation Spatial Data Framework data in NSW.

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Term Acronym Definition

Datum

- Datum (more recently called a Reference Frame) is a mathematical model of the earth that defines the origin, scale and orientation of a coordinate system against which features can be represented as coordinates.

Dynamic Datum or more appropriately: “Time-dependent Datum”

- A reference frame in which the defining parameters include time evolution. With a dynamic datum, the reference frame is fixed to the earth as a whole. As the earth’s tectonic plates move (by a few centimetres a year), a feature’s coordinates also change to reflect that movement. Examples include the WGS84 datum used by Global Positioning Systems (GPS), and the International Terrestrial Reference Frame (ITRF).

Datum Ensemble

- A group of multiple realizations of the same terrestrial or vertical reference system that, for approximate spatial referencing purposes, are not significantly different

Epoch A point in time, as applied to time dependent datums, expressed in decimal years. Example 2017-03-25 in the Gregorian calendar is epoch 2017.23. See also Coordinate Epoch and Observation Epoch.

European Petroleum Survey Group Code

EPSG Code

Online database that contains definitions of numerous datums and map projections, along with formulas to translate between them. Each is uniquely identified via an EPSG code. See https://www.epsg-registry.org/ Note that ISO 19127:2019 has been developed to further standardise this information and will in future replace the EPSG defacto standard

Global Positioning System / Global Navigation Satellite Systems

GPS / GNSS

Satellite delivered navigation systems which provide geo-spatial positioning with global coverage, allowing small autonomous receivers to determine position, altitude and time.

NSW Foundation Spatial Data/ Foundation Spatial Data Framework

FSD FDSF

The NSW Foundation Spatial Data Framework (FSDF) provides a common point of reference for the assembly and maintenance of foundation level spatial data held by NSW Government agencies. It contains the best available, most current, authoritative source of foundation spatial data under ten foundation themes.

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Term Acronym Definition

Geocentric Datum of Australia 1994

GDA94 The national Australian mapping datum in force from 1994 to 2017, superseded by GDA2020.

Geocentric Datum of Australia 2020

GDA2020 The current Australian mapping datum. Gazetted by the Commonwealth according to the National

Measurement (Recognized-Value Standard of Measurement of

Position) Determination 2017 (https://www.legislation.gov.au/Details/F2017L01352)

Map projection Coordinate conversion from the earth’s ellipsoidal coordinate system to a plane.

Observation Epoch

The date/time at which the data was observed or measured; the date/time of data acquisition.

Reference Frame

See – Datum

Spatial data Data that identifies a geographic location, usually stored as coordinates and can be mapped.

Static Datum A reference frame in which the defining parameters exclude time evolution. With a static datum, the reference frame is locked to the regional tectonic plate; features on a static datum have coordinates which remain the same over time. For example, both GDA94 and GDA2020 are static datums for Australia.

Web Mercator WGS84 Web Mercator (EPSG::3857) is the defacto standard projection used in web-mapping. (Its official name is “Pseudo Mercator”). WGS84 Web Mercator is projected from the WG84 datum ensemble (EPSG::6326).

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Term Acronym Definition

World Geodetic System

WGS84 WGS is a geocentric mapping datum first developed by the United States Department of Defense [sic] in 1960 (as WGS60). WGS has since evolved with continued improvements to the measurement and modelling of the global system and is currently referred to as WGS84. The ‘WGS84 datum’ is not a single unique reference frame; it has been updated six times to date, with significant changes (up to 0.7m) especially between older realisations. WGS84 is also time-dependent, changing coordinates in Australia at 7 cm per year. Together, these realisations form a datum ensemble, which should be taken to have an accuracy of several metres, and to be appropriate for approximate spatial referencing purposes only.

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8. Related policies and documents

Issuer Reference Document Name

DFSI Version 2.0 May 2018

NSW Standard for Spatially Enabling Information

www.spatial.nsw.gov.au

Spatial Services | Department of Customer Service

Address: Level 14 West McKell Building 2-24 Rawson Place Sydney NSW 2000

Email: GDA2020@customerservice.nsw.gov.au