Updated March 2, 2023
Introduction to RTK
RTK which stands for Real-Time Kinematic is originated in the mid of the 1990s and is a differential GNSS technique that provides great positioning performances around the location of its base station. This is one of the techniques which is used to increase the accuracy of GPS (Global Positioning Systems) with the help of a fixed and stable base station that can send the corrections to the moving receiver in a wireless manner.
What is RTK?
Real-Time Kinematic is a carrier-based ranging the technique that can provide ranges and positions with a good accuracy that order of more precise compared with code-based positioning techniques. It is a satellite-based positioning or navigation based system which is derived from Global Navigation Satelite Systems (GNSS) such as GPS, Galileo, GLONASS, NavIC, BeiDou. RTK is used for those sorts of applications where we require centimeter-level accuracy in the range of 1cm + 1ppm and since this is more accurate it is a bit complex as well. The main architectural components of RTK are the base station, Rover users who can be one or many, and a communication channel through which base the station can communicate the user in real-time.
With reference to GPS, these RTK systems are commonly referenced as carrier-phase enhancements or CPGPS and this has found its applications in land Survey, unmanned aerial vehicle navigation, and hydrographic survey.
The general concept is that the distance between the satellite receiver and the satellite can be estimated by the time that is taken for the satellite signal to be received at the receiver. Since the satellite signal takes time to reach the receiver and the receiver must align to the pseudorandom sequence that is part of the signal received with the system internally generated pseudorandom binary sequence. In this way, the two sequences can be eventually aligned to obtained better accuracy and precision. RTK follows this general concept but uses carrier waves as its signal ignoring the information contained within. A fixed base station and a rover to reduce the rover position error are the part of it and the fixed base station is supposed to pass the data to the rover.
The range to a satellite is calculated by multiplication of the carrier wavelength and the number of whole cycles between rover and satellite and addition of the phase difference. In the above calculation solving the number of whole cycles is not trivial and hence the calculation can have an error as there is can shift in phase by one or more cycles. This is called an integer ambiguity search problem and solving this problem will provide better accuracy and precision. This error can be greatly reduced by many sophisticated statistical methods and resulting in better precision.
It is observed that RTK uses a single base station which is a fixed base station and multiple numbers of mobile units and there are multiple ways with which the correction signal can be passed to the different mobile stations. UHF band the radio modem is one of the one such typical ways by using which we can achieve low cost and real-time signal transmission.
Why we need RTK?
RTK is one of the most critical features of the surveyors. In the world of drones to survey the land, RTK has been the boon to obtain precession in surveying. Many civil architectures use this particular RTK in getting their design to accuracy and construct the structure. If you look into designs with UAV technology using RTK and without RTK then you will understand the level of precession that can be obtained by using RTK
In real-time kinematic RTK, the carrier phase observables or the required corrections are broadcasted from the referenced base station to the mobile. Thus making it possible to calculate the required positions at the precession of centimeter-level in the real-time and respectively warn the operator when a re-initialization is required.
Another major application of RTK is in the filed of Hydrographic survey or marine surveying position on the globes surface and depth of the sea is determined. In hydrographic surveying, numerous technologies have been introduced but the usage of RTK has its own prominence. Surveyors started using GPS in surveying simpler as well as complex profiles. But in hydrographic survey reading the important parameter are the tidal reading, depth, and positioning. RTK is the most significant method with which we can get the depth and position simultaneously for the hydrographic readings.
Another area where RTK is vastly used is unmanned aerial vehicle navigation where the UAV systems equipped with Global navigation satellite system GNSS and RTK a low cost and high precision alternative many other sensors and here the accuracy of GNSS based the receiver is improved by sending the correction signals by the fixed base station. These RTK systems will enable them to locate the precise location of UAV systems with the precession of a few centimeters.
Importance of RTK
There are many advantages of using RTK systems in various fields of surveying using GNSS. Few of them are listed below
- These are commodity-based systems hence their cost and maintenance is quite cheaper compared to other commercial sensors which will serve the same purposes
- RTK networks have extended circumference of area RTK usage containing the network of reference stations. The operation reliability and the accuracy of the survey depends on the density, hardware, and capability of referenced base station networks
- CORS which is Continuously operating reference station is again a network of RTK base stations that are used to transfer the corrections usually over the internet. And since more base stations the accuracy in correction is
- The precession levels provided by RTK is to the level of few centimeters which is remarkable
- RTK has made possible to face many challenges faced by the surveyors in their surveying quite effectively with
- RTK has found its application in many areas and some prominent areas include the land surveying, UAV navigation, and Hydrographic Surveying where the depth and position of marine bodies are calculated quite efficiently
Conclusion
Although there are few limitations of RTK, these are most apt to sue in the fields of surveying. This article has listed a few major areas of RTK usage but there are other areas as well such as auto-drive and autopilot based systems, Machine controls systems, precision farming, etc
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