Geocentric Datum of Australia

Why a Geocentric Datum?
What prompted this need for a shift to a Geocentric Datum?
In 1989, the Inter-Governmental Council on Surveying and Mapping (ICSM) recommended that 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 ie, 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 in the year 2000 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 the Department of Land Information) in turn was given the responsibility for dealing with all technical issues associated with GDA94.

For a detailed background and overview of the introduction of GDA in Western Australia please access Mr Robert Holloway’s (WALIS GDA Consultant) paper entitled 'The Introduction of the Geocentric Datum into Western Australia'.

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Transformation of the Tengraph database to Geocentric Datum of Australia (GDA) took place on December 18th 2000. Some functionality changes have been made to assist industry in a smooth transition from the AGD grid to the GDA grid.
These included:
 

• The ability to view dual grids (AGD grid or the GDA grid or both) under menu function selections /graticule grid 
  
•  Standard prints can be generated with the existing AGD grid or the GDA grid or both 
  
•  Provisions have been made to easily identify ‘Print Object Details’ in AGD or GDA datums. The GDA version displays the GDA logo and
  
• A GDA Conversion Calculator is available to convert geographicals or coordinates from AGD to GDA or visa versa, (under File menu).

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The then Department of Mineral and Resources (MPR) (now the Department of Mines and Petroleum (DMP)) supported the Inter-governmental Committee on Surveying and Mapping (ICSM) resolution to adopt the GDA and in association with WALIS and the then Department of Land Administration (DOLA) achieved full implementation within the Department on 18th December 2000.

DMP fully endorsed the introduction of GDA considering it a most effective datum for all users of it’s spatial data whether local, national or international, because of it’s spatial uniformity.

This was seen as an important factor now that DMP's TENGRAPH database and other geophysical spatial information systems can be accessed via the World Wide Web.

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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/Licences that are physically defined on the ground by survey or by applicants pegging retain their existing position under GDA. (ie their ground position does not alter). 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

Graticular Mining Exploration Licences are defined by a Graticular Block of 1minute of Latitude x 1minute 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 18th December 2000 did not move
• Graticular Exploration Licences lodged on or after 18th December 2000 were required to comply with the new GDA Grid (with New GDA coordinates)
• The boundaries of applications for Graticular Exploration Licences existing on 18th 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
  

Sec 57(4) Boundaries

Currently there exist 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.

Petroleum Titles

Petroleum Titles (both Onshore and Offshore) are defined on a 5 minute of latitude and 5 minute 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 contained.
The following principles were established:

• All Petroleum Titles lodged after 18th 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
  

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The move to GDA impacted the Geological Survey Division (GSD) extensively. GSD have a wide range of products affected. These included:

• Manuscripts
• State, Project, and Series Maps
• Airborne Geophysical
• Corporate Databases
• GIS Datasets
• Data held in spreadsheets and word documents
• Field Acquisition
• Geophysics (shot point location and seismic reflection data)
• Remote sensing data
• Digital Petroleum maps
• Miscellaneous physical holdings

If you require further detail on GDA's impacts upon you as a user of GSD products, please refer to our GDA contact for the Geological Survey Division

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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:
  http://www.landgate.wa.gov.au/corporate.nsf/web/WA+Grid+File
  http://www.icsm.gov.au/gda/gdatm/index.html

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MPR was firmly committed to the smooth implementation of GDA94 by December 18, 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.

Implementation Plan

Key MPR  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 MPR Implementation Plan for GDA Conversion was compiled.

This document discusses in depth, issues and procedures for conversion of MPR digital data and products from AGD84 to GDA94.

The DMP Divisions affected by GDA are:

• Geological Survey Division
• Mineral Titles Division
• Mining Operations Division 
• Petroleum and Royalties Division

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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 December 18, 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 datum (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
  

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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 to GDA. They also provide links to other GDA related sites.

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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

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You may have some specific questions on GDA relating to background information or questions of a more technical nature. ICSM has a very good GDA FAQ section that may be of assistance.

If however your question relates specifically to DMP, please go to our key contacts list on this page to locate the most appropriate person to assist in answering your question.

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GDA Brochures, Video and CD Rom

Going Geocentric CD-ROM
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 e-mail your contact details to AUSLIG GDA Promotions Officer

GDA Brochures Available On Line
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.

GDA Video
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.

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