GDA2020 & ArcGIS

It is now official on the 15th of December 2017 Geoscience Australia and the Intergovernmental Committee on Survey and Mapping (ICSM) launched the new GDA2020 datum.

In support of the new Australian datum, the following tools and resources have also been released by Geoscience Australia and ICSM:

• the ICSM GDA2020 Technical Manual
• additional ICSM datum modernisation Fact Sheets
• GDA94 to GDA2020 Transformation Grids
• Geoscience Australia’s GDA94 to GDA2020 Online Transformation Service
• AUSGeoid2020 to convert GDA2020 ellipsoid heights to the Australian Height Datum.

So what does this mean for the ArcGIS product suite? Well from ArcGIS Pro 2.1 and ArcGIS 10.6 onwards all state, territory and national projections that incorporate the GDA2020 datum are supported.

NOTE: This article refers specifically to ArcGIS 10.6 and ArcGIS Pro 2.1. For later versions of software please install the ArcGIS_Coordinate_Systems_Data_Windows software available from My.Esri to obtain the latest NTv2 files.

Transformations between the datum’s GDA94 and GDA2020 are also supported using both the mathematical seven-parameter similarity transformation or the NTv2.0 transformation grids. ICSM has developed two 2D national transformation grids:

• Conformal: simply a grid version of the seven-parameter similarity transformation: the basic difference between GDA94 and GDA2020 coordinates primarily due to plate tectonic movement (approximately 1.7m NNE over 26 years); and
• Conformal + Distortion: incorporates the conformal seven-parameter similarity transformation plus localised and regional distortion revealed by incorporating coordinates on ground survey control networks across the nation.

These transformation grid files can be downloaded from the ICSM Github site

In ArcGIS products these transformation methods are listed as

• GDA_1994_To_GDA2020_1 : seven-parameter similarity transformation
• GDA_1994_To_GDA2020_NTv2_C : Conformal Grid
• GDA_1994_To_GDA2020_NTv2_CD : Conformal + Distortion Grid

As the software is not delivered with the Grid files only the seven-parameter similarity transformation will appear in ArcGIS until the Grid files are loaded to the product directories:

• ArcGIS Desktop : Program Files (x86)\ArcGIS\Desktop10.5\pedata\ntv2\australia
• ArcGIS Server: Program Files\ArcGIS\Server\pedata\ntv2\australia
• ArcGIS Pro: Program Files\ArcGIS\Pro\Resources\pedata\ntv2\australia

And renamed:

• FROM GDA94_GDA2020_conformal.gsb TO AUS942020_C.gsb
• FROM GDA94_GDA2020_conformal_and_distortion.gsb TO AUS942020_CD.gsb

With this in place it is now possible to use the Project geoprocessing tool to convert from GDA94 to GDA2020.

A final note for ArcMAP & ArcGIS Pro Users, If you are displaying GDA94 data in a GDA2020 map frame then under the Map’s Transformation properties you need to specify the transformation to use before the GDA94 data is projected dynamically to GDA2020.

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