GDA Adjustment for Department of Main Roads (Central District)

Explanation of GDA (Geocentric Datum of Australia)

"The Geocentric Datum of Australia (GDA) is the new Australian coordinate system, replacing the Australian Geodetic Datum (AGD). GDA is part of a global coordinate reference frame and is directly compatible with the Global Positioning System (GPS). It is the culmination of more than a decade of anticipation and work by the Intergovernmental Committee on Surveying and Mapping (ICSM) and its predecessor, the National Mapping Council (NMC). When the NMC adopted the AGD84 coordinate set in 1984, it "recognised the need for Australia to eventually adopt a geocentric datum." This was further recognised in 1988 when ICSM "recommended the adoption of an appropriate geocentric datum by 1 January 2000"."

The promotional brochure distributed by the ICSM, Know Where You Stand With GDA, cites the following benefits associated with the implementation of the GDA:

* provide direct compatibility with GPS measurements and mapping, or Geographic Information Systems (GIS) which are based on the geocentric datum.
* minimise the need for casual users to understand datum transformations
* allow more efficient use of organisations spatial data resources by reducing the need for duplication and unnecessary translations
* help promote wider use of spatial data through one user-friendly data environment
* reduce the risk of confusion as GPS, GIS and navigation systems become more widely used in business and recreational activities

SCOPE:

The project involves the readjustment of Main Roads GPS Bench Marks (Central District) onto the recently introduced GDA94 Geodetic Datum. All marks have now been registered with the Department of Natural Resources and Mines and form part of the SCDB (Survey Cadastral DataBase).

Click here to view the many control stations and networks were incorporated into the one overall network.

DSS' Methodology

Dynamic Satellite Surveys have conducted GPS control surveys for the Department of Main Roads, Central District since 1993. Since that time, approximately sixty-seven separate control networks have been observed, providing the DMR with an infrastructure of coordinated Bench Marks along the State Controlled Road Network.

Up until now, all adjustments have been carried out on a project by project basis, with adjacent survey areas interlinked where applicable. The results have been reduced to AGD / AMG84, relative to the Survey Control Database (SCDB) coordinate datum, sourced from the Department of Natural Resources and Mines.

Adopting a cooperative developmental approach, DSS worked with DMR to develop and implement the Integrated Survey Grid (ISG). The ISG coordinate sets are derived directly from the AMG coordinates, and provide the Department with a convenient and practical datum suitable for all stages of the survey process.

The wealth of survey information generated over the years through the GPS control surveys undertaken, has been held in-house, by the DMR Survey section. With the implementation of the GDA, on a national basis, the opportunity was identified to transform all the existing individual survey networks onto the new GDA datum. In addition the formal registration of all the Bench Marks would allow them to be incorporated into the Queensland Survey Control Database (SCDB).

Conclusions

The completed GDA conversion of all the Main Roads Bench Marks, in Central District, has provided the Department with a uniform control network, compliant with the new national geodetic datum. The valuable public resource has been realised by their inclusion in the Survey Control Database (SCDB).

Dynamic Satellite Surveys will continue to use the GDA datum on all Main Roads jobs and are also implementing the new datum in other work areas.