The Geocentric Datum of Australia 1994 (GDA94) is Australia’s official geodetic datum. GDA94 is a static coordinate datum based on the International Terrestrial Reference Frame 1992 (ITRF92), held at the reference epoch of 1 January 1994. The standard map projection associated with GDA94 is the Map Grid of Australia 1994 (MGA94).
Survey Control Network
The accurate realisation of GDA94 is maintained in Victoria through the repeated adjustment of the Victorian survey control mark network of survey observations. This data set is regularly updated with new observations and readjusted to derive new estimates of survey mark coordinates. These refinements to the network enable the derivation of GDA94 coordinates on new survey marks and improved coordinates on existing marks.
Geocentric Datum of Australia 2020 (GDA2020) is a modernised geodetic datum for Australia which will be made available in Victoria over 2017 and 2018. GDA2020 is a conventional static datum based on ITRF2014 at the reference epoch of 1 January 2020. Information on GDA2020 implementation and transformation tools are available for the transition to GDA2020 through the Intergovernmental Committee on Surveying and Mapping (ICSM).
Register for updates and learn more by visiting the GDA2020 website
Visit the GDA2020 forum
You can download the GDA Technical Manual from the ICSM website
GDAit transformation software
The Office of Surveyor-General Victoria (OSGV) makes available software called GDAit for users to transform between AGD66 and GDA94 using geographical coordinates (AGD66 – GDA94) and UTM grid coordinates and zones (AMG66 – MGA94).
The transformation process uses a grid of latitude and longitude shifts. The shifts are a combination of a 7-parameter conformal transformation between AGD66 and GDA94 and the (modelled) distortion in AGD66.
GDAit (release version 2.02 22/11/01) has been updated for national use with grid data stored in the NTv2 format (Canadian Binary Format).
Please note that while every effort has been made to ensure the accuracy and currency of GDAit and the Victorian grid data, the State of Victoria does not accept responsibility for any actions arising from the use of the software or data.
Files included in the download
Install Instructions - how to install the software and grid on your computer, as well as a history LOG showing the changes that have occurred with the GDAit software and grid files during its development.
GDAit v2.02 (32 Bit for Windows 95 / 98 / 2000 / NT / ME) - download and then execute to automatically install GDAit onto your computer. The current grid file will have to be manually imported into GDAit once the GDAitsoftware has been installed.
Note: the latest grid file is downloaded separately from the GDAit software. Please see the link to the ICSM website below regarding the grid file and its download.
A National Transformation Grid File is available from ICSM and replaces all previous versions of the grid files (Victorian, south-east Australia, etc.).
Visit the ICSM website
The complete national coverage from AGD to GDA is 3.2MB. This coverage was generated using the latest algorithms with data from the previous AGD state and territory grid files and AGD and GDA data from the National Geodetic Data Base.
The national file also covers the offshore areas out to the Exclusive Economic Zone (EEZ). The grid is supplied in the NTv2 format and a simple conformal (7-parameter) transformation was used to generate the shifts in these offshore areas.
GDAit User Guide
Download the GDAit User Guide – same as the online help included in the software download.
Download GDAit Software Documentation – explains the GDAit software architecture, including the bi-linear interpolation technique used to interpolate the transformation grid file.
GDAit DLL for software developers
GDAit DLL is the Dynamic Link Library version of GDAit that transforms coordinates between AGD (66/84) and GDA and vice versa. The DLL is freely available for download and use by developers to incorporate into their software (provided appropriate acknowledgement of Land Use Victoria is included).
Download GDAit Dynamic Link Library (ZIP, 25.9 KB) with accompanying documentation describing the functions contained in the DLL and how to call them from C or Visual Basic. For detailed information on the transformation process please refer to the GDAit user guide and software documentation above.
AMGVG conversion software
Download and then execute the program to perform calculations with coordinates. Note this software does not transform coordinate information between AGD and GDA, either geographical or UTM grid coordinates.
To change between AMG and MGA input screens, enter either A or M respectively at Select Option.
When in the MGA mode calculations for Vicgrid are performed relating to Vicgrid94 specifications.
MGA computational manual
Further information on MGA94 is available in the MGA Computational Manual:
- The Map Grid of Australia 1994 Computational Manual (PDF, 217.2 KB)
- The Map Grid of Australia 1994 Computational Manual (DOC, 1.5 MB)
Scale factor calculations
A spreadsheet to assist with computing Point Scale Factor, Height Factor and Grid Convergence calculations is available for download.