Introduction
The CORS users may utilize the CORS real-time services by applying for a subscription.
Global Navigation Satellite Systems (GNSS) has revolutionized our ability to access location information. In nutshell it measures its distances from a bunch of satellites hovering over the earth in predefined orbits, through radio signals and estimates its own position on earth. However these system has its own share of error budget due to Orbit errors, Satellite Clock error, Receiver noise, Ionospheric and Tropospheric delays, Satellite Geometry over receiver and multipath etc, which causes dilution in its precision up to 10 -11 meters. To overcome this accuracy limit, various Surveying techniques such as DGNSS, Static GPS/GNSS surveying, RTK, SBAS, GBAS, and PPP are being used by Geospatial community. Each of these method works own principal of taking GNSS measurement.
In most of GNSS applications where precise positioning is required, users usually pair their GNSS instruments with other GNSS instruments, simultaneously observing one or more known position, termed as reference station, and with help of these reference stations estimated corrections to be applied over point of interest or rover position are obtained through Static GNSS Survey or Real Time-Kinematic (RTK) Survey methods. To facilitate users by not requiring to set up their own reference station each time they wish to undertake GNSS measurement, and provide country wide consistent reference frame. Survey of India has established a network of Continuously Operating Reference Stations (CORS), which not only capable of providing Real Time Positioning Service through RTK/NRTK with an accuracy of + / - 3cm, but also host an array of different positioning services targeted to cater requirements for different segments of Geospatial and scientific Community. These networked CORS stations (or GNSS receivers) are permanent installations and continuously stream satellite observations to a central server. The entire setup of Reference Stations and Central Server is known as Continuous Operating Reference Station (CORS) Network. The central server running specialized software performs calculations to further refine the rover position by sending Network Real-Time Kinematic (NRTK) corrections to the rover. The distance between a GNSS rover and the corresponding base station is no longer an issue. Users can subscribe to CORS network on monthly or yearly basis to receive NRTK corrections with their rover instead of having to set up their own base station. The CORS network is available 24 hours per day, 7 days a week and 365 days a year. However, it depends on the communication Service Provider and satellite availability. Data streaming of RTCM 2.4, RTCM 3.2 is supported in real-time and users can also retrieve stored GNSS data from the central server via the internet for post-processing. Users can also submit static survey GNSS data for online processing.
