JONATHON POWERS

The NSW Department of Lands is rolling out a $6 million electronic survey infrastructure. When completed, the entire state will be covered by a network of continuously operating reference stations that receive signals from navigation satellites.
 
The project will increase the absolute accuracy of the survey control network.
 
Currently, the survey control network is a state-wide complex of trig stations and permanent survey marks that have known latitude, longitude and heights. This provides the basis for all mapping and surveying in the state.
 
Over the past 50 years, more than 220,000 of these points have been established. Many were placed for mapping purposes, or during rural surveys. As a result, more than 60 per cent have a known latitude, longitude or height – to various levels of uncertainty – based on the Geocentric Datum of Australia.
 
Most of these established marks are in the developed areas of the state.
 
Information about all the marks and their metadata, including accuracy, are available online through the Survey Control Information Management System.The proposed network would deliver significant improvements in both the accuracy and versatility of this infrastructure.
 
Under the new plans, 6000 trig stations will be decommissioned. A further 500 will be preserved and upgraded with accurate co-ordinates to ensure traceability of survey data, and for their heritage value.
 
Lands will also upgrade several key electronic distance measurement test lines, which are used by surveyors to comply with changing technology standards and capabilities.
 
Where feasible, existing trig sites located on crown reserves will be used for the new reference stations. However, unlike trig stations, they do not need to be located on hilltops. All that is required is a 360 degree view to the sky for uninterrupted access to satellite signals, and convenient power and data communication line services. This means that where practical, the department can use its existing regional offices to locate reference stations in regional areas.
 
No additional legislative changes will be required. Existing regulations allow the use of GNSS technology for surveys. Surveyors are also required to provide co-ordinates for any unco-ordinated marks close to their survey. This will improve coverage and the density of values across the state.
 
The new network will be known as NSWNet. It began in 2003 as seven sites in the Sydney metropolitan area, known as Sydnet. It was extended with additional sites at Nowra, Newcastle, Goulburn and Bathurst. It is now being expanded to the state’s north coast.
 
Lands is aiming to have the new data centre operating early next year. It will progressively establish at least 50 new stations that will be strategically located across the state, about 125 kilometres apart.
 
This year’s goal is to have management software operational for the first 25 sites, and for the remaining sites by the end of 2012.
 
The equipment at the six existing sites will be upgraded this year. The trig stations to be retained and preserved will be identified by mid-2012.
All survey information delivery systems for the infrastructure network will be integrated by the end of 2014.
 
The project includes the upgrade of data servers and management software. This will ensure that up to 100 stations in the network can be remotely managed and that users will have access to satellite positioning data services through the internet.
 
In the initial project rollout, all sites will be capable of receiving signals from both the GPS and Glonass constellations. The next generation of equipment, which will most likely be acquired from 2015, should be capable of receiving many constellations.
 
The European Galileo system will be operational by then. So will the Japanese QZSS system and the Chinese Compass. It is unclear whether the Indian IRNSS will be ready and if so, whether it will be available in NSW in that timeframe.
 
Regardless of the signal received, all sites will send to the data centre servers in real time. These servers are currently located at the Australian Technology Park in Redfern, Sydney.
 
At the data centre, the data stream is decoded and stored for users to request and download later. It is also provided to the NTRIPCaster (Network Transmission of RTCM data via Internet Protocol broadcaster) format. It provides error data in real time via the internet or mobile internet services, similar to the way that internet radio works.
 
This data is suitable for RTK. The accuracy depends on distance from individual stations and is set by the equipment supplier. It is typically less than 35 kilometres. There are no plans at this stage to broadcast GNSS corrections via dedicated radio frequency.
 
NSWNet will be developed in co-operation with the federal Auscope project. Ten of the 50 new stations will be built to upgraded specifications to meet the requirements of geospatial science and research. Although they will be built by the Commonwealth, the department will assume responsibility for their operation and maintenance.
 
The scientific objective of Auscope is to generate a millimetre-accurate virtual model of the Australian continent in order to understand and measure geophysical changes and patterns.
 
Output from these ten stations will be used both for NSWNet, and for the Auspos service provided by Geoscience Australia. Currently, the Auspos correction is derived from the Australian Regional GPS Network. Under the new dispensation, these – and stations in other states that run under similar arrangements with state authorities – will contribute to Auspos position solutions.
 
Products and service-level agreements are being developed between the Commonwealth and participating jurisdictions.
 
One implication of the project is that people creating and using digital maps and plans can use the same co-ordinated survey system. It will mean that spatial information stored in plans, aerial images, emergency dispatch systems, land titles, utility service plans, and a whole range of other spatial data can be more accurately matched up, joined or integrated.
 
NSWNet is being developed as a commercial-grade service. LPI plans to release product details, including service standards and availability, as part of its customer consultation process.
 
Other benefits will flow from the network’s accuracy. It will enable heights to be more efficiently obtained for existing survey marks, and deliver more accurate cadastral and topographic data.
 
Accurate heights for survey infrastructure benchmarks are important when dealing with complex strata and stratum developments, or mining. They are also important in resource management such as water and flood mitigation studies, sea level monitoring and climate change.
 
NSWNet will be an integral part of the positioning landscape in the state for the next generation of surveyors. It will be used for machine guidance in the agriculture, construction and mining industries. It will take less time for utilities to complete asset surveys, and for local government to undertake engineering, surveying and mapping activities.
 
It will mean improved productivity for private surveyors and for government departments and agencies carrying out transport planning and construction projects.
 

Jonathon Powers is an engineering writer living in Sydney.

Issue 40; April – May 2009