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O U T L O O K and sending data. The data from the base stations is continuously being sent to and received from a Master Control Centre (MCC) over mobile networks or the internet. i. Base station network The "Virtual Reference Station" principle is based on having a network of GNSS reference stations continuously connected via data communication link to a control centre. A computer at the control centre continuously gathers the information from all receivers, and creates a living database of Regional Area Corrections. These are used to create a Virtual Reference Station, situated only a few meters away from the location of rover together with the raw data, which would have come from rover. The rover interprets and uses the data just as if it has come from real reference station. The resulting performance improvement of RTK is dramatic. With "Virtual Reference Station Concept", it is possible to perform highly improved RTK positioning within the entire station network. The expected horizontal position accuracy is 1 – 2 dm when distances between actual reference stations are within 300km and 1 - 2 cm when distances between actual reference stations are approximately 50-70 km. Please note that the optimum distance between the reference stations depends on the geographic location of the network, i.e. areas with higher ionospheric activity (TEC) might require a denser network. Fortunately, India comes under moderate ionospheric activity. With the availability of better GNSS satellite configuration and more signals, the determination of precise positioning has become more robust. Advantages of the Real Time Network RTK System i. No user base station is necessary as is required in the DGPS setup. The user needs only half the equipment to produce RT work (or, conversely, one can double productivity). Additionally, there is no lost time setting up and breaking down the base station equipment and radio. 2 2 G I S R E S O U R C E S | M A R C H 2 0 2 1 ii. No start and end points are necessary as is required in the ETS setup. So no time is lost in providing start and end control points. iii. Half the manpower is required as compared to the DGPS system and one fourth the manpower as compared to the ETS system. iv. There is considerable reduction in cost and time in the execution of the project. v. The first order ppm (part per million) error is eliminated (or drastically reduced) because ionospheric, tropospheric and orbital errors are interpolated to the site of the rover. This enables centimetre level positioning at extended ranges over 10 kilometres from a reference station. vi. The network can be aligned with the National Reference Frame with high accuracy. The users will then be collecting positional data that will fit together seamlessly across the Real Time Network coverage. This is important to all users of geospatial data, such as GIS professionals who by using good RT practices may deal with such regional issues as emergency management and security issues. vii. Different formats and accuracies are readily available. GIS data, environmental resource data, mapping grade data, etc. can be collected with 30 to 60 centimetre accuracy while surveyors and engineers can access the network with upto 2 centimetre level accuracy. RTCM, CMR+ and other binary formats can be user selected. viii. The RTN can be quality checked and monitored in relation to the National Reference Frame using utilities such as OPUS from NGS and TEQC from UNAVCO. As the name suggests, a real time network would require a network of base stations continuously receiving Design of the Real Time Network RTK System One element that is most readily associated with planning and design of a Real Time Network RTK is the base station spacing and geometry. As with any network of sensors or emitters; to cover as broad an area with as evenly and with as few nodes as possible, an array of stations in a pattern forming equilateral triangles is best. While an RTN is not simply "solving triangles" as is mistakenly assumed by looking at a map of an RTN, a pattern of equilateral triangles does also provide an optimal geometry for certain types of network modelling and for post-processing services and users. Spacing is a fundamental cost variable. There are many factors governing optimal spacing (per your RTN goals for performance/risks). Even the most well planned theoretical spacing will be subject to site-specific considerations. The regular equilateral triangle pattern will in reality be unlikely to achieve. Finding suitable sites near your desired locations can be challenging. It is not always a direct trade-off between compromised site conditions and optimal geometry as there are many options to mitigate for less than optimal site conditions (see construction) as well as some flexibility in geometry (perhaps through slightly closer spacing). ii. Suitable base station site The quality of data that is sent and received from the site Availability of real-time communications Availability of reliable power Secure site availability A brief summary of site conditions that may directly influence options for spacing:

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