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In the last decade, a number of correction services for global navigation satellite systems (GNSS) precise positioning have been developed, mainly for offshore applications, based on a precise point positioning (PPP) real-time processing. These allow receiving corrections without the need for an internet connection or reference benchmarks around the survey area. In the paper, we tested the Atlas correction service implemented in a Stonex S900A machine (Monza, Italy), with the purpose to verify its performances under optimal operational conditions and in the practical case of a land survey on several benchmarks along the Adriatic coast. The data analysis focused on: accuracy with respect to the reference frame, repeatability of the coordinates considering short and long acquisition periods, time to initialize the survey, and reliability of the formal errors provided by the instrument. The system confirmed the declared performances in most cases and is shown to be a viable alternative to other GNSS techniques also for land surveys where no obstacles affect the sky visibility.

Until a few years ago, a precise survey was only possible using global positioning system (GPS) and Global'naja Navigacionnaja Sputnikovaja Sistema (GLONASS) constellations, but the result was not guaranteed under conditions of poor sky visibility, as in urban canyons. Currently, the number of Global Navigation Satellite System (GNSS) satellites in orbit has strongly increased thanks to the great evolution of the Galileo and the Beidou constellations. In this paper, we investigate the impact of using different constellations and their combinations, in static positioning with the classical differencing approach. For this purpose, two distinct baselines of different lengths (10 and 60 km) were processed using commercial software over a period of one year (2018.24-2019.24). Data were acquired by permanent stations belonging to the European Permanent Network (EPN) network providing 24-h observing sessions. Two datasets were tested, one consisting of 24-h Receiver Independent Exchange Format (RINEX) files and the other considering only 2-h sessions of data acquisition. In both cases, a one-year-long time span has been considered. The baselines were processed considering each of the four GNSS constellations and a series of combinations, for a total of eight solutions. Results have been evaluated looking at the accuracy and repeatability of the coordinates, together with the main constellation parameters. During the analyzed period the number of contemporary visible satellites of the BeiDou constellation was still too poor over the considered area, and therefore this constellation did not provide comparable precisions in respect to the others. Positioning precision provided by the Galileo constellation has shown to be very close to those given by GPS or GLONASS, with a significant difference only on the height component, especially in the case of processing 2-h data. As for 24-h observing sessions, the use of multiconstellation observables actually leads to small improvements in precision with respect to the use of GPS data only, mainly appreciable considering the vertical component. The GPS-Galileo combination gives quite the same performances of the GPS-GLONASS one, but it can potentially take advantage of the integrity message provided by the European constellation.