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:
| EPSG | Name | Type / description |
|---|---|---|
| 1150 | GDA94 to WGS84 (1) | Null Transformation to WGS84 ensemble. Approximation at +/- 3m using assumption that GDA94 is equivalent to low accuracy WGS84 (ensemble) |
| 9688 – New | GDA94 to WGS 84 (2) | [Non-Null] 7 parameter transformation: Equivalent to 8048 plus (null) 8450 |
| 9689 – New | GDA94 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 – New | WGS 84 to GDA2020 (3) | [Non-Null] 7 parameter transformation: Equivalent to 8048 plus (null) 1150 |
| 9691 – New | WGS 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:
| Name | Type | EPSG |
|---|---|---|
| GDA2020 to WGS84 | Null Transformation to WGS84 ensemble | 8450 |
| 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:
| Name | Type | epsg |
|---|---|---|
| GDA94 to WGS84 | Null Transformation to WGS84 ensemble | 1150 |
| 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
Esri Australia Technical Blog 