Coordinate Transformations Between GDA94 and GDA2020

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The information in this article applies to:

• LISTECH Neo version 17.11.1.1 and later
• LISCAD SEE version 12.2 and later

Overview

The various jurisdictions in Australia are transitioning to the new national datum GDA2020. The ICSM has provided 3 methods of transforming data between GDA94 and GDA2020.

1. Conformal transformation using a 7 parameter Bursa-Wolf transformation
2. Conformal grid transformation
3. Conformal plus distortions grid transformation

Which transformation should I use?
Transformations (1) and (2) are intended for when the survey was connected to datum via GPS/GNSS (e.g. HxGN SmartNet). The way that the reference stations are coordinated means that they do not include local distortions. Hence, the transformation of related survey data only needs to account for the continental plate movement that has occurred between the different epochs of GDA94 and GDA2020. These two transformations are equivalent (using either one will produce the same result).

Transformation (3) has been provided for surveys that were connected to datum via local ground control marks. Due to the way that the different states and territories computed the GDA94 coordinates of their survey control networks, distortions were introduced. The error varies between jurisdictions and can be up to the decimetre level in magnitude.

Procedure

Transforming from GDA94 to GDA2020 using LISTECH Neo:
In order to apply a transformation in Neo, the Transform module is required.

Using transformation (1):
The 7-parameter transformation is included in the default project templates of Neo. If your project is using one of the predefined ‘GDA94/ MGA Zone XX’ coordinate systems (where XX is the zone number), then the transformation can be applied by the following:

1. Select Manage / Configuration / Set Coordinate System
2. Select the new coordinate system as the matching ‘GDA2020 / MGA Zone XX’ coordinate system
3. Select the ‘GDA94 to GDA2020 / MGA Zone XX’ transformation

If your project is on the Plane coordinate system but uses MGA coordinates, you should use Set Coordinate System command above to first change to the appropriate ‘GDA94/ MGA Zone XX’ coordinate system without applying any transformation.
Note that the pre-configured transformations in Neo are set to only transform the Easting and Northing coordinates because it is assumed that orthometric heights (i.e. elevation above AHD) are used in Neo. If the project uses ellipsoidal heights, then the transformation should be edited via Manage / Configuration / Coordinate Systems / Transformations and the ‘Preserve Orthometric Heights’ option turned off.

Using transformation (2):
There is no real reason to use this transformation. Transformation (1) provides the same result and is easier and faster to use. If desired, transformation (2) can be applied by following the same steps as transformation (3).

Using transformation (3):
Due to the size of the grid files, Neo does not include the grid transformations out of the box.

1. Download the grid file from https://github.com/icsm-au/transformation_grids/blob/master/GDA94_GDA2020_conformal_and_distortion.gsb
2. Create a new transformation using Manage / Configuration / Coordinate Systems / Transformations
3. Give the transformation a Name and Reverse name
4. Set the From coordinate system as the appropriate ‘GDA94/ MGA Zone XX’ coordinate system
5. Set the To coordinate system as the appropriate ‘GDA2020/ MGA Zone XX’ coordinate system
6. Set the Transformation Type as ‘Grid File (NTv2)’
7. Use the Grid File control to open and load the grid file that you downloaded in step 1
8. Accept the changes by pressing OK
9. Following the steps as for transformation (1) above but select the transformation you just created

Transforming from GDA94 to GDA2020 using LISCAD:
In order to apply a transformation in LISCAD, the Transformations module is required.

Using transformation (1):
The 7-parameter transformation is included in the default transformations of LISCAD. If your project is using one of the predefined ‘Map Grid Australia 94 Zone XX’ projections (where XX is the zone number), then the transformation can be applied by the following:

1. Select Task / Transformations / Projections / Transform Projection
2. Select Projection Type as ‘Transverse Mercator’
3. Select the (new) Projection as the matching ‘MGA 2020 Zone XX’
4. Select the matching ‘MGA 94 Zone XX to MGA 2020 Zone XX’ transformation

If your project is on the Plane coordinate system but uses MGA 94 coordinates, you should use the Transform Projection command above to first change from Plane to the appropriate ‘Map Grid Australia 94 Zone XX’ projection without applying any transformation.
Note that you can choose not to transform the elevations by selecting the “Do not transform elevations” check box. You must select that option if your original elevations were orthometric (i.e. AHD) and you wish to retain them after transformation.

Using transformation (2):
There is no real reason to use this transformation. Transformation (1) provides the same result and is easier and faster to use. If desired, transformation (2) can be applied by following the same steps as transformation (3).

Using transformation (3):
Due to the size of the grid files, LISCAD does not include the grid transformations out of the box.

1. Download the grid file from https://github.com/icsm-au/transformation_grids/blob/master/GDA94_GDA2020_conformal_and_distortion.gsb and store it in the “User Folder” language sub-folder.
2. Select Task / Utilities / Configure / Projections / Manage Transformations
3. Select Transformation Type as 'Projection', From Projection as the appropriate 'Map Grid Australia 94 XX' projection and To Projection as the appropriate ‘MGA 2020 Zone XX’ projection
4. Select the ‘New’ button to display the ‘New Transformation Scheme’ dialog
5. Set the From Projection as the appropriate ‘Map Grid Australia 94 XX’ projection
6. et the To Projection as the appropriate ‘MGA 2020 Zone XX’ projection
7. Give the transformation a Name and Reverse name
8. Set the Transformation Type as ‘Grid File’
9. Select Format as ‘Grid File (NTv2)’
10. Use the File Name control to open and load the grid file that you downloaded in step 1
11. Save the new transformation by pressing OK
12. To apply the transformation, follow the steps as for transformation (1) above but select the transformation you just created

 

Further Information

Refer to the ICSM website: http://www.icsm.gov.au/what-we-do/geocentric-datum-australia