Australia on the move? Geodetic surveyors dispel GDA2020 confusion

By on 16 August, 2016


Australia is indeed on the move, with the Pacific tectonic plate moving in a northeasterly direction by about 7cm each year. However, this change is nothing new unlike the mainstream media shave been suggesting as of late. reported recently that “Australia’s on the move, and it’s starting to cause problems for science, farmers — and self-driving cars.” The Huffington Post ran a story titled “Australia Is 1.5 Metres Away From Where You Think It Is.” Forbes ran an even more dramatic story titled “Australia Will Suddenly Jump 5.9 Feet North On New Year’s Day.” Granted, only so many characters can be used in news title to explain this complex matter and news sites have an obligation of attracting readers’ attention with exciting titles.

However, these titles are misleading and discredit the excellent work of Australia’s experts from Geoscience Australia and the Intergovernmental Panel on Surveying and Mapping (ICSM) that are behind the move to GDA2020. In fact, the only reason all of this is coming to the world’s attention is the fact that Australia is one of the first countries in the world to make the ambitious move towards a dynamic datum. The move will have the valuable role of supporting future positioning needs for applications like driverless vehicles and centimetre-accurate personal navigation.

To untangle the conflicting messages Spatial Source spoke to Richard Stanaway, a geodetic surveyor who has consulted to governments on datum issues and is the director of precision surveying software company Quickclose.

“From a datum integrity perspective, the media suggesting that GDA94 is 1.5 m in error is wrong,” Stanaway claims. “GDA94 is a snapshot of the global ITRF frame at the 1st January 1994.”

Indeed, this difference has always been understood and quantified by monitoring stations across Australia, including the Australian Fiducial Network. Australia’s current datum GDA94, like most other national datums the world over, adopts an epoch to define the datum and is expected to differ over time from the ITRF datum used by satellite navigation systems like GPS.

“The relative accuracy of GDA94 across the continent has actually been in the order of a few cm for the Australian Fiducial Network) since 1994,” explains Stanaway. “Recent adjustments have tightened that down to 2-3 cm.”

Therefore in practice, the coordinates across Australia are actually accurate to 2-3cm continent wide.

Where the difference arises is in the use of GNSS systems like GPS, which are based on the space-fixed ITRF datum, rather than earth-fixed datums like the existing GDA94. Since the Earth’s crust is moving relative to this datum this creates anomalies when using satellite positioning, and this is generally the case the world over. It just so happens that the divide is larger in Australia than in most other countries and Geoscience Australia and ICSM are looking to address this in order to support future technologies.

ABC News therefore had the right idea in reporting that “Driverless cars need Australia’s latitude and longitude coordinates to be corrected.” They also spoke to the right sources by interviewing Dan Jaksa from Geoscience Australia who has been a prominent figure of late in the move towards GDA2020 (Jaksa’s article “Moving Australia into the future” in the December/January issue of Position magazine explained the need to change in full).

“While there is some work to be done by organisations to make the change to GDA2020,” Jaksa said. “…the cost of not doing this outweighs the cost of doing it.”

The cost of not doing this outweighs the cost of doing it.”

“At the moment [smart devices] have to adjust everything because the information you have doesn’t line up with the [physical] position.”

The solution proposed by ICSM and its Permanent Committee on Geodesy (PCG) is to create a datum that continuously keeps updated, known as a dynamic datum. The frequently quoted 7cm that the continental plate is moving is also an oversimplification, as the movement on one side of the continent is fractionally different on the other. To compute the differences, the Raijin supercomputer at Australia’s National Computing Infrastructure (NCI) will be used to update the datum on a daily basis. These coordinates will then be fed into the systems that use satellite positioning to ensure coordinates are aligned to known coordinates.

Ideally, the change will be an automated process, but for those that work with location data such as surveyors and GIS professionals, there will be an increased need to understand the dynamic datum and the data derived from it.

For ordinary members of the public, there is no expected change as things like property boundaries will continue to rely on relative coordinates. Managing director of aerial surveying firm AEROmetrex Mark Deuter explained that the new datum would have “no perceptible effect on people’s everyday lives.”

“However there are now global positioning systems that we need to align with,” he said.

“What is being implemented is a revision of the Australian coordinate systems to match the new position of Australia to the global mapping systems.”

When it comes to organisations who work with spatial data, however, Richard Stanaway is one of many who expects to see costly teething problems.

“Moving to GDA2020 will require some effort and cost,” he says. “There will also be inevitable confusion.”

“Moving to GDA2020 will require some effort and cost. There will also be inevitable confusion.”

“Ultimately the spatial industry would need to start developing their workflows to handle real-world dynamic datums, for example with 4D geodetic transformations and deformation models.”

“Having GDA2020 and GDA94 [running simultaneously] will add to confusion with the industry and precise users, because in practice GDA and MGA are widely used to describe coordinates.”

Earlier in the year, ICSM held a questionnaire aimed at assessing the general knowledge of the move to a dynamic datum. The recently released results included a 67% majority of respondents who did not envisage significant issues implementing GDA2020. This was despite 25% of respondents not being familiar with the fundamental difference between the two types of datums.

To address this, Stanaway believes ICSM, GA, state geodetic agencies and CORS operators will need to ensure that all current users of GDA94 who use GNSS CORS to access GDA94 have patches in place to ensure a smooth transition to GDA2020.

Still confused? Refer to Daniel Jaksa’s article “Moving Australia into the future” in the December/January issue of Position magazine.


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