No…sorry to disappoint you, but we are not talking fashion here, but the reference system we use to locate places on the Earth! We refer to these as geodetic coordinates—and a big change to the system will be coming soon. Councils, Constructing Authorities and Engineers regularly request us to supply As-Constructed survey data (and some design survey data) in GDA (Geocentric Datum of Australia) coordinates. Because the survey data is uniformly orientated and coordinated to fit with all of the other data sets, it can merge seamlessly into existing GIS (Geographic Information Systems) databases.
To be more accurate
GDA94 has been the operating datum across Australia since 2000. It is based on Australia’s position on the earth as at 1 January 1994. Coordinates have been fixed (relevant to Australia) during this time, but have also been adjusted as more accurate measurements are taken. The Queensland Department of Natural Resources and Mines supplies the coordinates for Permanent Survey Marks we use as the basis for some of our surveys. However, with the proliferation of orbiting satellites and better technology, it is time to progress to a more accurate datum.
Australia is on the move
Yes, it might surprise some that the whole of the country is moving! Australia’s tectonic plate is drifting in a north-easterly direction at a rate of 7 centimetres a year. That means that the "fixed coordinates” from 1994 are now approximately 1.8 metres out of position when compared to world coordinates. It is now possible to get real-time, sub-30mm accurate coordinates from orbiting satellites. Interestingly, this technology will even soon be readily available on smartphones and other devices. To keep up with this technology and the availability of accurate coordinate data, Australia will adopt GDA2020 as the datum for its coordinate system on the 1 January 2017. This datum will also be fixed, and will be based on calculated coordinates for Australia’s position in 2020.
Implications
So, how will this affect us? Users of survey data will need to be careful when working between the different coordinate systems. From 2017, new data will be in GDA2020 coordinates, and these will not mesh with any existing data on GDA94.
How many metres in a kilometre?
That is a trick question—the answer it seems is not so simple as saying 1000 metres! In Bundaberg, one kilometre measured on the earth’s surface is 999.6 metres using GDA coordinates.Many would not be aware that scale factors come into play when a curved surface (the earth) is projected onto a flat surface (i.e. a map). This scale factor changes depending on location but a general scale factor for Bundaberg is 0.9996. So one kilometre measured along the ground becomes is really 999.6 metres using GDA coordinates. This is important for Engineers and designers to keep in mind when they request data in "GDA” coordinates. Yes, constructing a kilometre-long bridge with a 40-centimetre gap in it would not be a ‘good look’!
Just something to think about!!!
Connecting our surveys to GDA datum is demanding and time-consuming, an expense that is part of our survey costs. Ultimately, however, it is beneficial overall as the data is stored and used within GIS databases to improve the long-term efficiency for surveying, engineering and construction industries.
In practice
We are presently using GDA coordinates to map the gas pipeline being constructed from Price Street to the Bundaberg Port. Prior to the pipeline being buried, we are locating the welds joining the 13-metre lengths of pipe. This data will then be provided to the owner of the pipeline, who will be able to be merged it into their GIS and enable them to overlay property boundaries, roads and other attributes. Having reliable positional information will streamline future maintenance or repairs to the pipeline.