Australia’s on the move: Getting ready for GDA2020

The reference system that Australian location information is based on is changing.

PSMA Australia is formulating its GDA2020 transition plan.

We’re all reliant on satellite positioning.

Australians rely on satellite positioning systems daily – to use a smartphone for navigation, order a ride-share service, fly a drone or survey a land parcel, for example. Most smartphones and handheld devices have a positional accuracy of about ten metres, which is good enough for finding the nearest ATM or sharing your location on social media.

Commercial activities and emergency management, including surveying and dispatching an emergency vehicle, on the other hand, require a much higher degree of positional accuracy. Emerging technologies, such as autonomous vehicles and drone delivery services, will also require a high degree of certainty about position. A two-metre difference could mean disaster for an autonomous vehicle, and it could see a parcel delivered to the wrong location in a high-density area.

Satellite positioning systems calculate a device’s location using three coordinates relative to the centre of the Earth, which is fixed. It’s an Earth-centred, Earth-fixed reference system. However, Australian location data is based on an Earth-centred, plate-fixed reference system.

Earth Fixed Datum

Image: Intergovernmental Committee on Surveying and Mapping

We’re drifters.

The Earth's crust is made up of tectonic plates that constantly move – sometimes called continental drift – and Australia sits on one of the fastest moving. It’s moving north-north-east at a rate of about seven centimetres per year.

Australian location features, including addresses, roads and property boundaries, are mapped relative to Australia's tectonic plate, not the fixed centre of the earth, so the constant movement of the plate means a divergence occurs between GPS coordinates that are Earth-fixed and Australian location data that is plate-fixed. By 2020, the divergence will be up to 1.8 metres.

Australia's tectonic plate moves north-north-east at a rate of seven centimetres per year.

Image: Intergovernmental Committee on Surveying and Mapping

For many users of location services and applications, the 1.8 metre shift isn’t important. However, accounting for the shift is essential in high precision applications and for some emerging technologies. It will also benefit consumers as handheld device technology advances and satellite constellations improve.

Let’s get technical.

The standard that defines the Earth-centred, plate-fixed reference system for Australian location data is being modernised to account for the shifting continent. The Geocentric Datum of Australia 2020 (GDA2020) is new and replaces the Geocentric Datum of Australia 1994 (GDA94). Its implementation is being overseen by the Intergovernmental Committee on Surveying and Mapping (ICSM).

Incidentally, the standard that defines the Earth-centred, Earth-fixed satellite positioning reference system is the World Geodetic System 1984.

Key dates

There’s no official date yet proposed for adopting GDA2020, although the ICSM working group commenced implementation in 2018.

PSMA Australia is formulating its GDA2020 transition plan now.

Implications and impacts

The transition to GDA2020 will affect anyone in the spatial industry responsible for taking ground measurements, surveying, mapping, managing and delivering spatial information, and those managing and delivering geographic information systems.

In the broader community, the transition to GDA2020 will largely go unnoticed, however, everyone will benefit from access to up-to-date location data when using their handheld devices and navigation systems.

As PSMA transitions to GDA2020, it’s important that our customers, partners and end users know the datum on which our products are based. The transition will see spatial features in most of our data products shift north-north-east by 1.5 to 1.8 metres. Below is an example of how the transition will impact Geoscape® building footprints.

The impact of GDA2020 on Geoscape.

Image: PSMA Australia. Basemap: Open Streep Map

How we’re responding to the change.

We’re consulting with our partners, customers and end users to understand how best to support them in the transition to GDA2020. Following that, we’ll communicate a transition plan that fits with their needs. If you wish to input to the transition plan, please get in touch.

 

For more information on the GDA modernisation, refer to the Intergovernmental Committee on Surveying and Mapping.

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