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The Geocentric Datum of Australia 1994 (GDA) - Home
INTRODUCTION " The Geocentric Datum of Australia (GDA) is realised by the coordinates of the Australian Fiducial Network (AFN) geodetic stations, referred to the Geocentric Reference System 1980 (GRS80 Ellipsoid) and determined within the International Earth Rotation Service Terrestrial Reference Frame 1992 (ITRF92) at the epoch of 1994.0. To following are standard definitions and should be used without modification: GDA: Geocentric Datum of Australia GDA94: Geographical Coordinates (latitude and longitude) MGA94: Grid Coordinates (Universal Transverse Mercator Projection - easting, northing, zone) " The above definitions are sourced from the Intergovernmental Committee on Surveying and Mapping (ICSM). GDA is the new geocentric geodetic datum adopted by Australia on January 1 2000 and supersedes the Australian Geodetic Datum 1966 (AGD66) used in Victoria. Since its availability all organisations desiring to achieve optimal accuracy and improved data consistency have been migrating their data to GDA. Land Victoria is leading the change to GDA and this is being achieved through the development of information programs and transformation tools. GDA is part of a global coordinate reference frame and is directly compatible with the Global Positioning System (GPS) and for all practical purposes the same as WGS84, which is the datum of GPS. BACKGROUND Excellent background information is available from National Mapping Division - Geoscience Australia and ICSM. ICSM has also produced a GDA Technical Manual. FURTHER INFORMATION Further Information can be found on the GDA, including Ellipsoid parameters, Australian Fiducial Network (AFN) and Australian National Network (ANN) facts. Land Victoria is committed to ensuring the transition to GDA is as smooth as possible. Land Victoria contracted the University of Melbourne to undertake an investigation on moving to the new datum. The following report was produced. A follow up report was then produced, called Based on this work a transformation grid for Melbourne and Environs was developed. The following report details the development of that grid. Since the production of this report, the grid was extended to cover the remainder of the state and integrated with an equivalent NSW grid in 2000. The following report details the development of that grid. In addition a National Transformation Grid File (13.09.2001) has been produced which and replaces all preceding Victorian specific grid files. GDA COORDINATE SYSTEMS There are two types of coordinate systems used with GDA and they are: GDA94 - Geographical Coordinates (latitude and longitude). Geographical Coordinates are also referred to as Geodetic Coordinates. Latitude and longitude are curvilinear coordinates and are a function of the size, shape and location of the reference ellipsoid. Geographical coordinates are also dependant on the definition of the datum and for any given datum, latitude and longitude uniquely define the location of a point on the surface of an ellipsoid. Victorian Example:
MGA94 - Grid Coordinates (UTM - easting, northing, zone). The standard map projection associated with GDA is the Map Grid of Australia, 1994 (MGA94), a transverse mercator projection, which conforms with the internationally accepted Universal Transverse Mercator Grid system. The UTM zone system is used to enable co-ordinate references between zones to be unique. Victorian Example:
For further information on MGA94 please refer to MGA94 - A Simplified Computational Manual TRANSFORMATION OPTIONS Users of spatial data in Victoria will increasingly need to transform coordinates between AGD66 and GDA. There are several different methods that can achieve a transformation of coordinates between datums, all of which produce results with different accuracies. A brief description of some of these methods and the recommended Land Victoria approach is given in Transformation Options. USEFUL TOOLS In an effort to aid the process of converting to GDA, Land Victoria has developed some Useful Tools. These tools include a software program called GDAit which can be downloaded and used on a variety of platforms on your PC, or can simply be executed on the WEB using the GDAit Web utility. GDAit will transform coordinates (geodetic coordinates and grid coordinates) between AGD66 and GDA within the coverage area of National Transformation Grid File, see current Coverage Map. MIGRATING TO GDA The migration of data to GDA from 2000 onwards will bring about change for many users of spatial data. This page provides information about Migrating to GDA. Further information about the Draft Victorian GDA94 Map Information Block Guidance Notes is also available. GDA NEWS Keep up to date with the latest policy information and News on GDA. This document was last reviewed on 23/03/2006.
© 2007 by the State of Victoria
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