A datum is a mathematical surface on which a mapping or coordinate system is based. A geocentric datum by definition then has the centre of the Earth as its origin. The Geocentric Datum is one that best approximates the size and shape of the earth globally, due to the centre of its spheroid coinciding with the Earth's centre.
Work is underway on the implementation of the latest Datum update, to GDA2020.
The Geocentric Datum does not seek to be a good approximation of any part of the Earth in particular. Unlike the former Australian Geodetic Datum (AGD), which was designed as a best representation for the land mass of Australia, the Geocentric Datum is designed primarily to unify global spatial information.
Reasons for the shift to Geocentric Datum
In 1989, the Inter-Governmental Council on Surveying and Mapping (ICSM) recommended Australia adopt a geocentric datum by the year 2000, to be known as the Geocentric Datum of Australia 1994 (GDA94).
Some compelling reasons for this recommendation were:
- Compatibility with the emerging GPS surveys and satellite navigation systems which also use Geocentric coordinates (WGS84) World Geodetic System 1984
- Local, regional, state, national and international compatibility, such as one consistent reference frame for all users
- provides necessary infrastructure to support international agreements
- unification of all the different mapping datum across Australia into one homogenous datum.
On 4th June 1996 the Western Australian Government, in recognition of the ICSM recommendations, approved the adoption of the Geocentric Datum of Australia 1994 for all government agencies.
To facilitate this decision the Western Australian Land Information System (WALIS) Council was given the responsibility for overseeing the smooth introduction of GDA into Western Australia. The then Department of Land Administration (DOLA), now Landgate, was given the responsibility for dealing with all associated technical issues.
Tengraph® and Tengraph® Online
Transformation of the Tengraph database to Geocentric Datum of Australia (GDA) took place in December 2000. Some functionality changes have been made to assist industry in a smooth transition from the AGD grid to the GDA grid.
- the ability to view dual grids (AGD grid or the GDA grid or both) under menu function selections or graticule grid
- standard prints can be generated with the existing AGD grid or the GDA grid or both
- provisions to easily identify ‘print object details’ in AGD or GDA datums. The GDA version displays the GDA logo
- a GDA conversion calculator to convert geographicals or coordinates from AGD to GDA or visa versa.
The department’s GDA Policy
The then Department of Mineral and Petroleum Resources (MPR), now the Department of Mines and Petroleum, supported the ICSM resolution to adopt the GDA and in association with WALIS and the DOLA achieved full implementation within the department in December 2000.
The department fully endorsed the introduction of GDA, considering it a most effective datum for all users of its spatial data whether local, national or international, because of its spatial uniformity.
This was seen as an important factor now that the department’s TENGRAPH database and other geophysical spatial information systems can be accessed via the internet.
Impact on mining and petroleum tenements
The basic principles for GDA implementation and its effect on mining and petroleum tenements can be identified as follows:
- the boundaries of all existing mining leases or licences that are physically defined on the ground by survey or by applicants pegging retain their existing position under GDA. However, the coordinate values of these positions alter by approximately 200 metres (equates to approximately 5” in latitude or longitude )
- existing graticular based mining exploration licences or petroleum permits defined by blocks retain their existing ground position under GDA.
Graticular mining exploration licences
These licences are defined by a graticular block of one minute of latitude by one minute of longitude, with each block having a unique alpha numeric identifier.
The following principles were adopted upon implementation of GDA:
- The boundaries of all existing graticular exploration licences existing on 18 December 2000 did not move.
- Graticular exploration licences lodged on or after 18 December 2000 were required to comply with the new GDA grid with new coordinates.
- The boundaries of applications for graticular exploration licences existing on 18 December 2000 will be granted under the old grid (AGD84) infrastructure.
- Gaps created where GDA exploration licence applications abut existing AGD grid licences can be applied for as prospecting licences or mining leases by any party, however, normal procedures apply including Native Title. These gaps can be applied for by description and on ground marking will not be required.
- Overlaps are created where GDA licences abut existing AGD licences. On the relinquishment of the AGD licence the overlap ground will be incorporated into the new GDA licence if it is still in force.
Section 57(4) Boundaries
Currently there are 12 designated Sec 57(4) areas across the State covering regions of high mining activity which exclude exploration licences. These areas originally conformed with the AGD grid and were declared under Sec 57(4) of the Mining Act.
Upon implementation of GDA these boundaries shifted to conform with the new GDA grid. This means that some existing AGD exploration licences will fall within the new Sec57(4) boundaries. However, any new GDA exploration licences will now abut the new Sec57(4) boundary.
Both onshore and offshore Petroleum Titles are defined on a five minutes of latitude and five minutes of longitude graticular block system, based on the AGD. Each block is numbered and referenced to the 1:1 000 000 map sheet from which it is contained.
The following principles were established:
- All Petroleum Titles lodged after 18 December 2000 are still to be described in the above manner. However all mapping of titles and pipelines will utilise the GDA coordinate system.
- Petroleum Titles are not affected by gaps or overlaps as a result of GDA implementation.
Impact on geological products
The move to GDA impacted the department’s Geological Survey of Western Australia (GSWA) extensively. A wide range of GSWA products were affected, including:
- State, project and series maps
- Airborne geophysical data
- corporate databases
- GIS datasets
- data held in spreadsheets and word documents
- field Acquisition
- remote sensing data
- digital Petroleum maps
- miscellaneous physical holdings.
If you require further detail on GDA's impacts upon GSWA products, please refer to our contacts page.
The following software is available for free download:
- WA Grid file - The Western Australian gridfile (wa_0701.gsb) is a free utility provided by Landgate, to accurately transform geographical coordinates from the Australian Geodetic Datum 1984 (AGD84) to the Geocentric Datum of Australia 1994 (GDA94), and vice versa. The grid file has been computed by Dr Phil Collier at the University of Melbourne, using a data set of 18,492 geodetic points adjusted by Geodetic Data Services, Landgate.
- GDAit NEW Version - GDAit (GDA94 InTerpolation) is software that can be used to transform coordinates from the current Australian Geodetic Datum (ADG66/84) to the new Geocentric Datum of Australia (GDA94). This is an updated version of GDAit released to accompany the WA grid. A user manual can also be downloaded with it.
- Software links - The free software downloads are available at the following links:
The then Department of Mineral and Petroleum Resources (MPR) was firmly committed to the smooth implementation of GDA94 by 18 December 2000. In order to achieve this, a departmental Steering Committee and a Working Group identified all strategic issues for consideration and developed a comprehensive implementation strategy.
Key departmental implementation dates for GDA were:
- 1/1/2000 - some maps and plans provided in GDA format
- March 2000 - The GDA conversion formulae (WA Grid file) made available to MPR for Database Transformations
- 18/12/2000 - The MPR Tengraph Database converted using the WA Grid File to GDA.
A detailed Implementation Plan for GDA Conversion was compiled.
This document discusses in depth, issues and procedures for conversion of the department’s digital data and products from AGD84 to GDA94.
Legislative amendments to the State Mining and Petroleum Acts were enacted to accommodate the introduction of GDA.
State Acts affected included:
- Mining Act 1978
- Petroleum Act 1967
- Petroleum (Submerged Land) Act 1982
- Mines Safety and Inspection Act 1994.
Acts Amendment Act
An Acts Amendment Act was proclaimed to amend all State Acts by removing any specific reference to datum and replacing it with a reference ‘as prescribed’. The ‘prescribed datum’ inserted into the Mining Regulations enables easier amendment should a new datum be proclaimed in the future.
Mining Act 1978 (WA)
As a result of a shift to the new GDA grid for new exploration licences on 18 December 2000 the Mining Act 1978 (WA) was amended to preserve the rights of existing exploration licence holders to ensure:
- Existing granted exploration licences and pending applications retain the same ground in accordance with the existing AGD
- Graticular blocks surrendered from exploration licences granted prior to GDA implementation be identified and defined in accordance with their original datum (AGD)
- Exploration licences lodged after GDA implementation are required to conform with the new GDA grid.
GDA sites of interest
There are various websites related to the Geocentric Datum of Australia.
These sites will assist in furthering your knowledge on some of the more technical aspects of GDA; provide a comprehensive background; and explain the benefits of the move. They also provide links to other GDA related sites.
Technical manuals and papers
For those who wish to further investigate the technicalities of the GDA, the following links may be of interest:
ICSM GDA Technical Manual
Inter-governmental committee on Survey and Mapping.
An updated explanation of the Geocentric Datum of Australia and its effects upon future mapping
Technical Paper by Dr Will Featherstone of Curtin University.
Other technical papers can be found on ICSM's GDA website
Frequently asked questions
You may have some specific GDA questions relating to background information or technical details. ICSM has a very good GDA FAQ section that may be of assistance.
If, however, your question relates specifically to the department, please go to our key contacts list on this page to locate the most appropriate person to assist in answering your question.
A CD ROM entitled Going Geocentric is now available.
It contains a promotional video, brochures, a technical manual and information factsheets for Australia and New Zealand. Grid transformations for available jurisdictions and also transformation and software development tools are also located on the CD-ROM.
If you would like a free copy of the Going Geocentric CD-ROM, please email your contact details to AUSLIG GDA Promotions Officer
The following GDA brochures are available for downloading from the ICSM website.
Get In Step With the Geocentric Datum - Discussing the Business Issues
Know Where You Stand with GDA
Both brochures can be viewed using your current browser or can be viewed in PDF format, by downloading Adobe Acrobat Reader.
A non-technical introductory video ‘GOING GEOCENTRIC - Understanding Australia's new coordinates’ was produced and is available for distribution. The video is designed to be used as an introduction to GDA. If you would like a free copy either:
Call 1800 800 173 or email AUSLIG.