CORS Networks

 

This image from think spatial depicts the existing CORS around Australia. This thesis aimed examined a subset of these networks, which are listed below.

CORS Networks

CORS networks are advantageous over single baseline GPS for many reasons. Such advantages include:

  1. Elimination of base station issues (Reduced cost for hardware, security, set up time)

  2. Elimination of radio issues

  3. Common co-ordinate system used by all parties

  4. Reduced insurance costs

  5. Increased working range (mobile coverage becomes the biggest limitation)

Some CORS networks in existence already are described below. It is acknowledged that this does not cover every network in Australia, however, the aim is to examine a handful of significant networks.


CORSnet-NSW

CORSnet-NSW is a government network currently consisting of 47 sites. It is run by the Land and Property Management Authority and is expected to expand to 70 sites by 2012. The final network is likely to be close to 100 stations (Pers. Comm., White, 2010). CORSnet-NSW produces “A continuous stream of GNSS data in RTCM format from a CORS broadcast to registered users via wireless internet” (Product and Service Definition). It allows realtime data at one second epochs or, 1Hz (LPMA, 2010a).


CORSnet NSW. Source (LPMA, 2010b)

CORSnet-NSW does not target specific user groups, but aims to provide the base positioning infrastructure. This allows for innovative applications to be developed by 3rd parties.

Currently, CORSnet-NSW allows for GPS and GLONASS satellites to be tracked, while the accuracy of the position is about 10mm ± 1 ppm for a 30 second observation period. The user equipment determines the accuracy achieved, however, it is expected that accuracies will be 2 cm for RTK and sub metre for DGPS.

CORSnet-NSW uses international data standards such as RTCM and RINEX. Additionally, data is provided in CMR+ format due to its popularity in agriculture. The services CORSnet-NSW provides are Network RTK, RTK DGPS and RINEX data.

CORSnet-NSW do not offer a pay-as-you-go service due to difficulty in administration. These products are currently under review and new products will be released soon.

Users have access to validation networks in Bass Hill and Newcastle. This is not a calibration service, but allows users to compare their results with that of CORSnet-NSW. Validation networks in other areas are available on request.

CORSnet-NSW intends to undergo a program of renewal, with each receiver having a lifespan of 5 - 7 years. It is the intention of CORSnet-NSW to maintain their network to the highest level and observe as many satellite signals as possible, thus providing their users with the choice of which satellite signals they use.


SmartNet Aus

SmartNet Aus is a joint initiative of Leica Geosystems and C.R. Kennedy. Their aim is to provide RTK and data services throughout Australia.


The current CORS in use by SmartNet Aus. Source: SmartNet Aus (2010).

These networks provide centimetre level real time corrections for applications such as surveying, construction, mining, machine guidance and precision agriculture. Across Australia, SmartNet Aus are using 128 stations. Currently, only two areas can provide a network solution; South Australia and South East Queensland. These areas use a variant of the MAC in their Spider software. The remaining stations provide single base positioning.

SmartNet Aus do not own their CORS infrastructure, but collect data sets and generate real time products based on the data streamed. The infrastructure belongs to government or private owners. Private owners are typically those that would use the service, for example, surveyors, precision agriculture users, etc. By contributing data to SmartNet Aus, CORS infrastructure owners receive a portion of each subscription which uses data from their CORS.

SmartNet Aus uses all standard data formats from RTCM 2.3 to 3.1. The system is perfectly backwards compatible and uses iMAX for legacy equipment. SmartNet Aus uses NTRIP as described earlier.

Available services include:
- single frequency and GPS constellation only
- multiple frequency and multiple constellations
- Annual or hourly RTK/DGPS
- monthly internet connectivity
- RINEX download
- Coordinate computation service.

All data is logged and archived. Any corrections computed are logged and stored for six months.

SmartNet Aus are committed to making use of the new satellite signals once they are properly established and have the potential to benefit users. It is worth noting that to make use of these new signals, SmartNet Aus is reliant on the infrastructure owners’ willingness to purchase a new, compatible receiver.

The web interface allows users to view which stations are online and available. Station quality summaries are available along with real time coordinate analysis.


SmartNet Aus Web Interface. Source: SmartNet Aus (2010).

Other features include Network Online Visualisation Accuracy (NOVA) Maps and Station Quality Summaries. These are displayed below in Figure 6.


Various online features offered by SmartNet Aus (2010).

The main interest of SmartNet Aus is to provide data corrections. While SmartNet Aus can sell direct to users (standard pricing options in Appendix 2), it is their preference to instead use Value Added Resellers. These VARs are free to set their own price and receive a commission for each subscription sold. The working goal is to have one set of infrastructure, but allow multiple VARs to service each client base. VARs can include competitors.


TopNET


A demonstration of a CORS user in the TopNET network. Source: Docherty (Pers. Comm., 2010).

TopNET is a joint venture between Topcon and Position Partners, distributors for Topcon equipment in Australia. TopNET mainly operates in Queensland from Brisbane to Mackay, but also has 4 stations in Victoria servicing greater Melbourne and one station in Rydalmere, NSW.

TopNET’s main clients include construction and GIS companies.

TopNET is able to provide RINEX data, RTK and DGNSS data. This service is open to all equipment brands. The data format will vary to suit the choice of receiver. Formats include RTCM 2.3, RTCM 3.0 and CMR+. Data can be provided at the very fast rate of up to 20 Hz. Each data file is logged, supporting the case for legal traceability.

This network has a benefit over competitors in that it has the ability to track satellites from GPS, GLONASS and GALILEO. At present, Galileo is not an active satellite navigation system.

For marketability, TopNET is available with various licences, depending on the application and length of time desired.

Currently, TopNET only provides a single baseline solution from their CORS stations.


Checkpoint


CORS around the world in use by Checkpoint. Source: Checkpoint (2010).

Checkpoint is an independent Network CORS service provider run under the business name South Australian CORS. Its goals include (Elliot, 2009):

- To provide a generic Network RTK solution
- To develop a network of CORS across Australia
- To provide an intelligent CORS management system
- To provide users with access to CORS corrections from the developing networks across Australia
- To build a CORS network where the user is the focal point of subscription and development.

Formats

Checkpoint is open to any brand of GNSS receiver that can accept standard industry formats.

Checkpoint promotes an in-house developed method for Network RTK corrections; Networked Reference Station (NRS). This correctional method can involve 5 CORS and gives weights to their impact on the position solution. NRS allows for positions to be obtained over very long distances to sub metre accuracies.

Along with NRS, Checkpoint can also provide MAC and i-MAC.

The Master Auxiliary Concept is promoted by Checkpoint as it:
- is the only internationally standardised Network RTK Method
- gives the rover control to calculate distance dependent error corrections
- is the most advanced method using more (RTCM 3.1) network information
- provides consistent results

The independent Master Auxiliary Concept:
- is the best individualised Network RTK method
- was developed for older receivers that do not support MAC (Checkpoint, 2010)

User Interface

Checkpoint is designed to be completely run via the internet. The user account is set up through a web browser and the interface allows the user to purchase a subscription, as shown in Figure 9. This online management systems gives users, Value Adding Resellers (VARs) and CORS owners access to individual levels of reporting, administration, accounting and data access.


Subscription purchase options. Note that these are standard options; subscriptions and pricing can be individually tailored. Source: Checkpoint (2010).

Checkpoint have a variety of VARs in Australia and around the world. These VARs are useful in giving specialist attention to niche industries and usually sell subscriptions with the purchase of GNSS equipment. Internationally, Checkpoint is working with VARs in India and in Singapore.


Value Adding Resellers in Australia. Source: Checkpoint (2010).

A list of CORS are also available to view. Figure 11 shows some of the online station information available to the user, including a map showing the station’s location, station info (such as status, latitude, longitude, elevation and mask angle), photographs of the station and the site log.


CORS station information available. Source: Checkpoint (2010).

Infrastructure

Checkpoint own several stations in South Australia, however, their goal is not to own the most infrastructure. Instead they encourage investment in CORS infrastructure by rewarding data sharing. Infrastructure owners who contribute to Checkpoint receive a portion of each subscription cost involved in the positioning of a particular user. This is illustrated below in Figure 12.  It should be noted that more than three stations could be involved in a solution and this would alter the subscription distribution to CORS investors.


Checkpoint Subscription Distribution Model. Source: (Elliot, 2009).

Future use of Satellite Signals

Checkpoint is very much committed to updating its positioning infrastructure. Investors in CORS infrastructure are obliged to retain a portion of the infrastructure’s income to allow for the purchase of a new receiver every seven years.

Vicmap Position - GPSnet


The GPSnet CORS Network. Source: GPSnet (2010).

GPSnet is a government run CORS network which spans across the entire state of Victoria. GPSnet is described as a multi-modal network, in that it can provide sub metre accuracy for mapping and asset management down to centimetre level accuracy for surveying, agriculture, etc.

GPSnet offers DGPS and RTK in both single baseline and network solutions. These are available in real time and also for post processing.

GPSnet supports multiple data formats including the standards such as RTCM 2.3 to 3.1 and RINEX and also CMR, CMR+ and CMRx.

The cost to use GPSnet varies according to industry and in most cases VARs are used to bundle the subscription with equipment.

At this time, GPSnet is currently tracking GPS and GLONASS satellites. In the future when more satellite constellations are operational, GPSnet will make use of the new signals.


AuScope Geospatial

AuScope Geospatial is an initiative of Geoscience Australia in collaboration with the Australian National University, University of Tasmania, Curtin University and all of the State and Territory Governments. It is planned for this program to be implemented by 2011. AuScope Geospatial is concerned with the deformation of the Australian continent and aims to upgrade the ground infrastructure through:

  1. Increasing the density of the network of GNSS CORS

  2. Establishment of an array of radio telescopes for Very Long Baseline Interferometry

  3. Enhancement of the satellite laser ranging (SLR) capability at Mt Stromlo, in the Australian Capital Territory, to allow more efficient ranging to high-orbiting satellites

  4. Establishment of a National geodetic gravity monitoring program.

This GNSS CORS network will eventually provide the foundation on which a new National Datum will be built (Johnston et al, 2008).

The AuScope CORS network allow access to the fundamental national geospatial reference frame and will be able to support standard high accuracy GNSS positioning applications (Rizos, 2008).

 

The AuScope Geospatial Project. Source: Johnston et al (2008).

AuScope logged GNSS RINEX data is freely available from a file transfer protocol.