Transitioning to GDA2020 The new Geocentric Datum of Australia

Roger Fraser

Office of Surveyor-General Victoria

2017 Vicmap Information Sessions

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Communication channels

• Animation �

• Factsheets

• Website: http://www.icsm.gov.au �

Modernising Australia’s Datum

• Register for Victorian e-newsletter:

http://gda2020.vic.gov.au

ICSM communications

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http://www.icsm.gov.au � Modernising Australia’s Datum � Online forum

ICSM communications

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Why GDA2020?

Drivers for a modernised geodetic datum for Australia

• Crustal dynamics and regional deformation

• Significant technological developments in underlying geodetic

infrastructure and user-community positioning devices

• Widespread distortions in GDA94

• GDA94 fails to support increasing accuracy needs of users

• All absolute positioning technologies based upon the

International Terrestrial Reference Frame (ITRF)

• Future mass market access to precise positioning

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Datum modernisation

• An ongoing and essential task for any country seeking to provide

accurate and reliable positioning for the community

Historical datum changes

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GDA2020 specifications and implementation

Two stage approach

Stage 1 – Geocentric Datum of Australia (GDA2020)

• Conventional static datum like GDA94 with rigorous uncertainty

• Just like GDA94 — based on ITRF, fixed at a specific epoch:

- GDA94 = ITRF1992 @ 1994.0

- GDA2020 = ITRF2014 @ 2020.0

• Horizontal shift of approx. 1.6 m NE from GDA94, with slight rotation

• Consistent vertical drop of 0.09 m from GDA94

• Available for adoption from mid February 2017

• Projections: MGA2020 (UTM), VICGRID (conformal conic)

• AUSGeoid2020 will be released with GDA2020

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GDA2020 specifications and implementation

Two stage approach

Stage 2 - Australian Terrestrial Reference Frame (ATRF)

• Initial release commencing January 2020

• Reference frame that caters for a dynamic Earth

• Aligned with ITRF, the reference frame in use by satellite positioning

• Will require supporting standards & the adoption of tools in major software

before widespread adoption is realistic

• Modernisation of AHD will be investigated

Plate-fixed GDA2020 (Stage 1) will be maintained until no longer needed

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GDA94

implementation

GDA2020 specifications and implementation

1994 2000 2017 2020 2023

@ 2000 @ 2017 @ 2020 @ 2023

-0.42m +0.21m -0.21m

@ 1994

GDA94 GDA2020

GNSS

+1.6m

GDA2020

implementation ATRF

implementation

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1mm

GDA94 to GDA2020 shift

1.60m

1.49m

Consistent 0.09m drop in ellipsoid height

1.58m

1.54m

1.52m1.56m1.58m

1.59m

1.57m 1.53m

1.55m

MGA94 MGA2020

MGA94

MGA94

MGA2020

MGA2020

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Next steps

Preparing for transition

1. Data audit

2. Systems audit

3. Educate stakeholders and suppliers

Source and lineage

Metadata

Awareness and

education

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Next steps

Data audit

• Identify critical spatial data

• Ensure critical data is tagged with correct Coordinate Reference System

• Identify what datasets need to be transformed, when they should be

transformed and critical dependencies

• Low accuracy or low resolution datasets may not require transformation

• Beware of WGS84!

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WGS84 – what is it aligned to now?

WGS84 is not what it seems

• WGS is the global reference frame that GPS is based upon.

• What is it aligned to?

WGS84 – original realisation completed in 1987

WGS84 (G730) – aligned with ITRF 1991 @ 1991.0

• Adopted Jan 1994

WGS84 (G873) – aligned with ITRF 1994 @ 1994.0

• Adopted Sep 1996

WGS84 (G1150) – aligned with ITRF 2000 @ 2001.0

• Adopted Jan 2002

WGS84 (G1674) – aligned with ITRF 2008 @ 2005.0

• Adopted in Feb 2012

WGS84 (G1762) – aligned with ITRF 2008 @ 2005.0 (no change)

• Adopted in Oct 2013

WGS84 (G…) – aligned with ITRF ???? @ ????

• Adoption ?

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IGS – what is it aligned to now?

What is post-processed GNSS aligned to?

• Post-processing requires precise orbits of GNSS satellites (from IGS)

• Precise orbit products aligned to different ITRF versions

Source: http://acc.igs.org/igs-frames.html

IGS = International GNSS Service (see http://igs.org)

ITRF 1992 02.01.1994 31.12.1994

ITRF 1993 01.01.1995 29.06.1996

ITRF 1994 30.06.1996 01.12.2001

ITRF 2000 02.12.2001 04.11.2006

ITRF 2005 05.11.2006 16.04.2011

ITRF 2008 17.04.2011 29.01.2017

ITRF 2014 29.01.2017 …

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Next steps

Systems audit

• Field equipment firmware support?

• Identify GIS and data management systems:

- On-the-fly transformation capability?

- Version and potential for upgrades?

• Data in proprietary/text files on shared drives,

database, or Web service (WMS/WMTS)?

• Watch out for custom built applications,

unsupported software/applications, or

legacy apps that ignore spatial metadata

• Is transition dependent on system capability?

• Users encouraged to contact software vendors

to determine GDA2020 support

• For any issues, post to GDA2020 Online Forum

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Next steps

Educate stakeholders and suppliers

• Know your metadata – datum, epoch, lineage, uncertainty

• Understand what datum data is captured in

• Ensure data providers are aware of your requirements,

and when you plan to adopt GDA2020

• Ensure data users are aware of GDA2020 and issues that

may arise

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Data, parameters, software and support

DELWP transition

• DELWP Implementation Plan developed

• System upgrades already commenced

• Dual support progressively available

from 3rd quarter 2017

• SMES (dual coordinates, sketch plans/reports,

Web services)

• GPSnet (dual GDA94/GDA2020 streams)

• Vicmap, Spatial Datamart (dual WMS/WMTS)

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Data, parameters, software and support

Parameters and grid files

• Official transformation parameters are available to convert

between GDA94 and GDA2020 and vice-versa

• 7 transformation parameters

• Plate motion model (Euler parameters)

• Also, 14 transformation parameters

(7 parameters + 7 rates of change) supporting:

• GDA2020 ↔ ITRF2014 and

• GDA2020 ↔ previous ITRFs (e.g. ITRF2008, ITRF2005, …)

Under development

• A 2D transformation grid file in the widely-used NTv2 format

• A 3D transformation grid file – HDF5 proposed (open source)

GDA94 GDA2020MGA94 GDA94 GDA2020Projection Geographic Cartesian Cartesian Geographic Projection

E, N, zone Lat, Long, height X, Y, Z X, Y, Z Lat, Long, height E, N, zone

MGA2020Transformation

by 7 params or grid

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Data, parameters, software and support

Software, tools, documentation and examples

• Online transformation tools and Web services (ICSM Web site)

• Updated transformation software – GDAy

• Surveying equipment firmware to support real-time transformations

• EPSG codes have been registered (GDA2020, MGA2020, Vicgrid2020)

• Adoption of parameters and grid within vendor software (late 2017 onward)

- GIS, Surveying, Engineering, FME

• Open source Python scripts, Excel spreadsheets, NaturalGIS (QGIS) plug-in,

PROJ.4/GDAL/OGR libraries, examples & user guides

• AUSPOS position summary report (GDA94 + GDA2020 + ITRF2014)

• GDA2020 Technical Manual (http://icsm.gov.au/gda/tech.html)

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AHD and AUSGeoid 2020

AHD remains unchanged

Major change from AUSGeoid09

• 9cm change in ellipsoidal heights

across Australia

Additions and improvements

• Improved gravity modelling

• Higher resolution (more data)

• Uncertainty

• Mean Sea Level model offshore

• Better in rugged terrain

Open source application

• To convert GNSS heights to AHD

heightsAUSGeoid2020 will be released for use with GDA2020

AUSGeoid09 will still need to be used with GDA94

Transitioning to GDA2020 The new Geocentric Datum of Australia

Roger Fraser

Office of Surveyor-General Victoria

2017 Vicmap Information Sessions