Some Frequently Asked Questions (FAQs) by GIS software users considering the migration of data, software and workflows to GDA2020 are outlined below.
Which version of the software do I need?
It is important to check which version of software is required to display, transform, and create data in GDA2020 data. Refer to the software provider's documentation. In all instances, if feasible, it is recommended to upgrade to the latest version. Most GIS software packages now provide support for GDA2020.
A note on NTv2 Grid Files: As recommended in Land Tasmania's GDA2020 Implementation Policy (and Choosing a GDA94 - GDA2020 Transformation) the vast majority of GDA94 – GDA2020 transformations should be performed using the conformal 7-parameter similarity transformation equation. Therefore, the default installation for most software packages and applications will be adequate since most software defaults to the 7-parameter transformation method. If the NTv2 grid files are required, they are usually available as an additional installation package, or the user may be required to download the grid files via the ICSM website and configure the software accordingly. Refer to the particular software documentation for those details.
How do I obtain data in GDA2020?
Land Tasmania will provide data in GDA2020, upon request, via Land Tasmania's data supply methods: OpenData, LIST Spatial Data Delivery, and Raster Data Supplies. Refer also to Land Tasmania Services and Applications Datum Summary
For Open Data and LIST Data Deliveries please contact the LIST Help Desk:
What tools are available for transforming data into GDA2020?
The best option for transforming data between GDA94 and GDA2020 is to use one of the many open-source or proprietary GIS software packages. However, Geoscience Australia provide a free online dataset transformation service, and ICSM provide a free coordinate transformation software package called GDAy, that may be used to validate other transformation tools.
Geoscience Australia (GA) Online Transformation Service
GA's AGRS tools and models page includes an online service for transforming the following datasets from GDA94 to GDA2020:
The following limitations apply to the service as at 1 June 2020:
- ASCII Grid
- The website only transforms data in one direction - from GDA94 to GDA2020
- Only geographic coordinates can be used - data must be in GDA94 latitudes and longitudes (EPSG:4283), the service does not accept MGA94 Easting, Northing and Zone (EPSG:28355)
- The service does not confirm the source data is in GDA94 where that metadata is available. For example, a shapefile that is in GDA2020 (EPSG:7844) may be uploaded and the service will still apply the transformation from GDA94 to GDA2020, hence shifting the data another 1.5 - 1.8 metres approximately. Ensure your data is in GDA94 (EPSG:4283) before using the service.
- The Conformal 7-parameter Similarilty Transformation option caters for a GDA94 3D dataset (EPSG:4939) - that is, the coordinates may include GDA94 ellipsoidal height. The majority of Tasmanian spatial datasets only relate to the 2D case of GDA94 (EPSG:4283).
GDAy 3.0 is available from the ICSM GitHub repository. Click on "clone or download" to download the program. Unzip the contents of the zip file and follow the installation instructions in the README.md text file.
The program allows for transforming coordinates between geographic GDA94 and GDA2020 and projected MGA94 and MGA2020 (any zone) in both directions. The user must configure the source and destinaiton coordinate system under the Tools => Coordinate System menu option.
Either a manually entered coordinates or a text file of coordinates can be transformed and / or reprojected (no file format other than a text file is supported).
The Help is comprehensive and should be referenced for more support.
GDAy Coordinate System Selection menu option
How do I migrate workflows and projects from GDA94 into GDA2020?
- Identify which coordinate reference system(s) your datasets are stored in - "know your data, know your datum"
- Familarise yourself with the transformations tools available in the software you are using.
- Transform your data. Look at the coordinate feference system of all data sources and transform into GDA2020 / MGA2020 where feasible. The best case scenario is to have all your data in the same coordinate reference system.
- Modify GIS software projects / documents so that the data is displayed in GDA2020 and always ensure that the metadata is updated accordingly - see Preparing Metadata to Accompany Spatial Data for further explanation.
- Configure "on-the-fly" transformations. Most GIS software packages will transform data "on-the-fly" into the display coordinate reference system if it is not feasible to transform all datasets into GDA2020. It is essential to understand how to configure the "on-the-fly" transformations in the particular software if this option is used.
How do I supply GDA2020 data to other users and organisations?
Refer to previous FAQ's above for details on how to transform data into GDA2020. Whether managing data within an organisation, or supplying data to others, it is essential to always do the following:
- The Coordinate Reference System (CRS) must be defined in the dataset when it is created / exported. For example, Esri shapefiles must have a .prj file which specifies the dataset's CRS.
- Metadata associated with the CRS of the dataset must be as complete as possible, including relevant information such as the transformation method if the data has been transformed, the accuracy of the data and any limitations in its potential usage.
- In particular, text / CSV or spreadsheet files of coordinates should never be provided to another party without the CRS and relevant information being explicitly stated.
- Refer to Preparing Metadata for Land Tasmania for further information and metadata examples.
How do I transform WGS84 / Web Mercator data into GDA2020?
Before transforming between WGS84 and GDA2020 a user or organisation must understand:
Refer to Web Mapping and WGS84 / Web Mercator page for current details on this topic.
- How "WGS84" has historically been applied in GIS generally and web mapping in particular.
- If using Land Tasmania web services, the current solution being applied by Land Tasmania.