New GDA2020 transformations for WebGIS


May 2021

Esri Australia has been working with Esri and ICSM to ensure that the ArcGIS system can support clients migration from the GDA94 static datum to GDA2020 static datum. The ArcGIS system now fully supports data transformations via 7-parameter similarity transformation, or NTv2.0 transformation Grids.

As a result we are now seeing many clients migrate their authoritative datasets to GDA2020 and requiring all delivered data is in this same static datum. State and national governments are now delivering foundational open datasets in GDA2020 as well

In parallel to this migration we are also seeing more clients taking up WebGIS and delivering data via web services instead of shipping datasets or producing PDF’s. This is enabling a greater uptake web and mobile GIS, providing better informed field operators and getting live data in the hands of people who need it as they need it.

These two waves of change have presented a significant challenge. While transformations existed between WGS84 & GDA94 and GDA94 & GDA2020, there existed no direct path from GDA2020 to WGS84. If you wanted to place GDA2020 data into WebGIS you had to transform you data back through GDA94 to WGS84. Effectively moving the data back to its old location prior to publishing. Many clients asked why????

It has been termed the WGS84 Projection dilemma. So what’s changing?

Well ICSM have been listening and over the past six to eight months have released a new set of transformations. These now enable direct transformations to WebGIS. These are as follows:

EPSGNameType / description
1150GDA94 to WGS84 (1)Null Transformation to WGS84 ensemble.
Approximation at +/- 3m using assumption that GDA94 is
equivalent to low accuracy WGS84 (ensemble)
9688 – NewGDA94 to WGS 84 (2)[Non-Null] 7 parameter transformation:
Equivalent to 8048 plus (null) 8450
9689 – NewGDA94 to WGS 84 (3)[Non-Null] NTv2 Conformal & Distortion:
Equivalent to 8447 plus (null) 8450
8450 – New
to ArcGIS
GDA2020 to WGS 84 (2)Null Transformation to WGS84 ensemble.
Approximation at +/- 3m using assumption that GDA2020 is
equivalent to low accuracy WGS 84 (ensemble)
9690 –  NewWGS 84 to GDA2020 (3)[Non-Null] 7 parameter transformation:
Equivalent to 8048 plus (null) 1150
9691 – NewWGS 84 to GDA2020 (4)[Non-Null] NTv2 Conformal & Distortion:
Equivalent to 8447 plus (null) 1150

So what does this mean to the ArcGIS user?

Well you can now hold the majority of your data in GDA2020 and share it to Web GIS and have GDA94 data transformed to WebGIS and it all aligns.

So if the majority of you data is held in GDA2020 and you want to align GDA94 data then us use:

NameTypeEPSG
GDA2020 to WGS84Null Transformation to WGS84 ensemble8450
GDA94 to WGS84 (2)[Non-Null] 7 parameter transformation:
Equivalent to 8048 plus (null) 8450
9688
GDA94 to WGS84 (3)[Non-Null] NTv2 Conformal & Distortion:
Equivalent to 8447 plus (null) 8450
9689

If you continue to hold most of your data in GDA94 and you want to align GDA2020 data then use:

NameTypeepsg
GDA94 to WGS84Null Transformation to WGS84 ensemble1150
GDA2020 to WGS84 (3)[Non-Null] 7 parameter transformation:
Equivalent to 8048 plus (null) 1150
9690
GDA2020 to WGS84 (4)[Non-Null] NTv2 Conformal & Distortion:
Equivalent to 8447 plus (null) 1150
9691

When will the new transformations be available in the ArcGIS System?

ArcGIS Pro – Version 2.8 – Released May 2021

ArcGIS Enterprise – Version 10.9.1 – Due to be released late Q4 2021

Note: ArcGIS Enterprise 10.9 does NOT have these transformations. Released May 2021

For further information this content was delivered in a webinar with Geoscience Australia, for which the recording can be found at:

Building better alignment: GDA2020 transformations for Web GIS

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