What is CORS Infrastructure?
Global Navigation Satellite System, or GNSS Technology, has completely changed the field of surveying. GNSS comprises a network of satellite constellations that transmit position, navigation, and time (PNT) information and is used throughout the world for determining the precise position or geographic location of persons and objects.
However, the inherent inaccuracies of GPS signals have been a major cause of concern for GNSS applications, resulting in their constrained usage in survey applications.
The Survey of India’s Continuously Operating Reference System (CORS) is an important geodetic infrastructure that tends to address these issues by enabling more accurate and real-time data collection for positioning, navigation, and mapping.
What is CORS and How Does it Work?
Put simply, the CORS infrastructure is a network of GNSS receivers that are “continually operating” and provide real-time, high-accuracy position, velocity, and timing data.
Advancing the RTK Technique
It comprises an RTK (Real Time Kinematic) base station system that disseminates updates, typically over an internet connection. The RTK method commonly involves using a single fixed base station to wirelessly transmit corrective data to multiple moving receivers or rovers. However, traditional RTK has the challenge of limited reference-to-rover range, which means rovers must be within a short range from the station to work.
The Continually Operating Reference Stations (CORS) network solves this challenge, whereby a network of stations is established 60-70 km apart. These CORS stations are located at known, stable locations across the country.
CORS Network Functioning
The GPS/GNSS signals transmitted from satellites in orbit around the earth are received by the CORS receivers in these stations and used to calculate the precise location of the receiver. The CORS receivers then transmit this location data to a central server where it is processed and made available to users in real-time. Users can access the data using a variety of methods such as web portals or APIs.
But how does the CORS Infrastructure help ensure more accurate GNSS measurements?
For this, the CORS Network uses a technique called differential positioning. It involves comparing the signals received at two or more receivers and using the differences in the signals to calculate the precise location of the receivers. The CORS Network uses a network of reference stations that are used to calculate corrections to the GPS/GNSS signals received at the CORS stations. These corrections are then applied to the GPS/GNSS data to improve the accuracy of the position calculations.
The sites are independently owned and operated by various agencies, who each share their data with NGS
While the CORS Network is managed by the Survey of India, it is a multi-purpose, multi-agency cooperative project that brings together various public, private, and academic institutions. It is also available for use by government agencies, private companies, and the general public.
Components of the CORS Network
Summarizing the above-mentioned process of CORS network functioning, we can conclude that the infrastructure is made up of the following components:
The CORS stations are the primary components of the CORS Network. These stations are equipped with GPS/GNSS receivers and are located at known, stable locations across the country. The CORS stations continuously receive GPS/GNSS signals from a constellation of satellites in orbit around the earth and transmit this data to a central server.
The reference stations are located at known, stable locations across the country and are used to calculate corrections to the GPS/GNSS signals that are received at the CORS stations. These corrections are then applied to the GPS/GNSS data to improve the accuracy of the position calculations.
The control centers are responsible for the management and operation of the CORS Network. The control centers receive the data from the CORS stations and process it to produce accurate, real-time position data. The control centers also provide user support and maintain the hardware and software used in the CORS Network.
Data Communication Network
The data communication network is used to transmit data between the CORS stations, reference stations, and control centers. The data communication network uses a variety of technologies such as satellite, cellular, and internet-based communication to transmit the data.
Benefits of the CORS Network Over Classical RTK
The CORS network was established by the Survey of India to meet the needs of various geospatial and scientific communities. Today, the CORS network infrastructure is capable of providing Real-Time Positioning Service through RTK/NRTK with an accuracy of +/- 3 cm, as well as hosting a variety of different positioning services for applications in surveying, building, and precision agriculture.
At the same time, the CORS network is also enabling shared positioning platforms with defined precision for surveying, mapping, and monitoring massive infrastructure projects – irrigation, railroads, canals, dams, smart cities, drainage planning, and state boundary management, to name a few.
Here are some of the major benefits of the CORS geo-positioning infrastructure over the shortcomings of the traditional RTK approach.
Improved Positional Accuracy
The CORS Network infrastructure helps drastically reduce the distance-dependent component that is an issue with the classical RTK method, for more homogenous positioning at different distances from the stations.
Even while operating at great distances and in challenging weather conditions, the CORS network infrastructure increases the reliability of ambiguous fixed RTK rover positions by many times. CORS network guarantees almost 100% uptime around-the-clock via permanent stations, stable communication links, and redundant server design.
The CORS geopositioning infrastructure offers a standard, seamless framework for the entire nation, available 24 hours a day, 7 days a week, and 365 days a year. The CORS network contains over 2000 stations, contributed by different organizations, and the network continues to expand.
Network station motions are continuously tracked, ensuring that they accurately define the reference datum and, hence, are more stable.
The CORS Network technology has the capacity to handle greater workloads without affecting performance, supporting GPS, GLONASS, and even futuristic systems like COMPASS and GALILEO.
Several users and applications, including traditional RTK & DGPS, networked services – nRTK & nDGPS, as well as innovative applications, can be supported concurrently by the centralized real-time network of CORS.
The potent CORS network software system incorporates information from older base stations and offers standardized RTCM (standards developed by Radio Technical Commission for Maritime Services – RCTM) rectification data in a variety of formats and rates. CORS also supports a variety of communication protocols, including TCP/IP (NTRIP), radio (UHF and VHF), and cellular (supporting GMS/GPRS, CDMA, and HSPA).
The Road Ahead
The National Geospatial Policy 2022 clearly highlights the continuing role of the Survey of India in maintaining the CORS infrastructure. The Survey of India has also been actively engaging with various stakeholders, including the Geospatial industry, to further encourage the adoption of CORS infrastructure services in the country.
The CORS Network is set to aid in the creation and updating of revenue maps, which is one of the biggest issues the nation is currently facing, as well as the building of substantial infrastructure projects.
Together with other GNSS networks like GPS, Galileo, and GLONASS, the NAVIC network will also be added to the system as an enhancement soon. With the NAVIC system developing at such a pace, strengthened by the CORS Network, India is on its way to becoming more independent and reducing reliance on foreign satellite systems in the future.
Clearly, the CORS network infrastructure is a game-changer for geo-positioning in India, thanks to its fault tolerance, time and cost savings, accuracy, and reliability.