Precise point coordinates in real time
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Questions and answers
The receiver must support transmission of raw observations via the RTCM protocol and have internet access. Most professional GNSS receivers offer this capability. If you use a personal device (a watch, tracker, or car navigation system), it is unlikely to record the phase of the received signal or to track signals on two frequencies, which would make it impossible to run the PPP algorithm. Only some Android smartphones can be connected to the service, but due to, among other things, the simple antenna design, the accuracies obtained will be far from centimetre-level. You can also contact us to confirm your device’s compatibility with our service.
Every GNSS receiver tracks the basic navigation signals in the form of pseudorandom bits transmitted by each satellite. These allow the distance to the satellite to be reconstructed — these are known as code observations, or pseudoranges, and their accuracy reaches a few decimetres or metres. More advanced receivers additionally track the signal’s phase, that is, the variation in the “instantaneous displacement” of the electromagnetic wave over time. The precision of such a measurement is 2 mm, and this is the key to achieving high accuracies in precise techniques such as PPP or RTK/RTN. Phase observations are not tracked by simple personal devices such as watches, car navigation systems, or most smartphones.
If your device is equipped with a so-called survey-grade antenna or better (in simple terms — an antenna larger than a matchbox), there is a fair chance you will take full advantage of the PIGEON service. After a dozen or so minutes of solution “calibration” (known as initialisation), the position accuracy will be better than 2 dm, while its repeatability should be at the level of single centimetres. The longer the receiver remains stationary, the better the accuracy and repeatability. If you move (on foot or in a vehicle), the accuracy should be better than 0.5 m, but this depends on the surroundings. It will decrease as sky obstruction increases (e.g. between buildings) — in extreme cases, re-initialisation will be necessary.
Your device should have constant internet access in order to send observations and receive coordinates in real time. If you do not have internet access, you can save the observations in the device’s memory and submit them to other free tools, e.g. the CSRS-PPP service.
Make sure your device can transmit code and phase observations (pseudorange and carrier phase) via the RTCM protocol. Every hardware manufacturer has different solutions, so we encourage you to consult the user manual. Once you register with the service and pay for your account, you will receive individual login credentials and an IP address to which the RTCM stream should be sent. We will assist registered users in correctly configuring the connection.
The RTK technique requires measurements to be carried out near other reference stations (e.g. within the coverage of the ASG-EUPOS network or other commercial providers), which determine local corrections to satellite observations. After a few seconds, a coordinate accuracy of 3 cm horizontally and 5 cm vertically is achieved, regardless of the weather, but with good sky visibility. Outside the coverage of the reference station network, the RTK technique cannot be used. The PPP technique can be performed anywhere in the world with just a single receiver. By using internet or satellite corrections, the PPP technique reliably reconstructs the errors in satellite measurements arising from satellite orbit modelling and signal propagation. As a result, it is possible to achieve better coordinate accuracy and repeatability than with RTK. The drawback is the long convergence time (a dozen or so minutes), which is why the PPP technique works excellently for continuous and/or static measurements, such as in displacement monitoring, and in open areas, where an initialisation, once obtained, can be maintained throughout the entire measurement period.
While most phase receivers have the RTK algorithm implemented (it is relatively simple to realise), at present only a few devices have a built-in PPP algorithm, and these are top-of-the-price-range devices or ones that work exclusively with commercial services. If your receiver has a built-in PPP algorithm, you probably bought it as a knowledgeable GNSS user and would not be asking this question. Otherwise, you can assume that your receiver does not have PPP functionality and, unfortunately, it cannot be “added” afterwards. Instead, you can use the PGON service, which will carry out the calculations that replace those performed by the receiver’s software.
