## Materials and Methods
### Tested Satellite Receivers  
Four GNSS receivers were used: Stonex S7-G; Stonex S5; Thales MobileMapper Pro; Quanum GPS Logger V2 (U-Blox NEO-6M). The satellite receiver Stonex S7-G (named S7) is able to receive L1 (1575.42 MHz) and L2 (1227.60 MHz) signals from GPS, GLONASS, BeiDou and SBAS (e.g., EGNOS) satellites; it has 120 channels, a maximum position update rate of 5 Hz (5 positions s\({}^{-1}\)), a size of \(234\times 99\times 56\) mm and a weight (without battery) less than 900 g, and it is also powered by a battery of 11.1 V and 2500 mA. The internal antenna has a choke ring which can suppress multipath satellite signals. This receiver is equipped with a Cortex-A8-AM33X processor with a frequency of 1 GHz, internal memory of 8 GB, external memory of 8 GB on SD board and RAM of 512 MB, as well as working with a Windows Mobile 6.5 Professional operating system. The receiver S7-G is also equipped with a slot for a SIM card and a GSM/GPRS/EDGE modem, which allows a quick and effective Internet connection, in order to obtain differential correction data in real time from the network of RTK ground stations (CORS). This receiver is equipped with Wi-Fi and Bluetooth connections, as well as a high brightness colour TFT display Blanview \(480\times 640\) VGA, allowing an interface with the measured or previously logged data, by providing the user with excellent visibility of the field work. This instrument is also equipped with a camera with a resolution of 5 MPixel and autofocus. The horizontal (2D, longitude and latitude)  
Figure 1: Representation of the testing field and UNIPA Global Navigation Satellite System (GNSS) Continuously Operating Reference Stations (CORS) station (coordinates are given in Gauss-Boaga Coordinate System). accuracy specified by the manufacturer is 5 mm + 1 ppm rms (root mean square, i.e., 63-68% of measurements) in static (stand-alone) mode, 0.6 m rms by using SBAS satellites, 0.4 m rms in differential mode (only code), 20 mm + 1 ppm in RTK mode with internal antenna, 10 mm + 1 ppm in RTK mode with external antenna. The satellite receiver Stonex S5 (named S5) is able to receive only L1 signal from GPS, GLONASS, BeiDou, QZSS and SBAS satellites; it has 372 channels, a maximum position update rate of 20 Hz (20 positions s\({}^{-1}\)), a size of \(119\times 86\times 32\) mm and a weight (without battery) of 290 g, and it is powered by a battery of 3.7 V and 3700 mA. This receiver is able to receive differential correction signals through Bluetooth and Wi-Fi connections, in order to reduce the positioning error, and is equipped with an AM355X processor, having a memory of 4 GB and RAM of 512 MB and working with a Linux operating system. The horizontal accuracy specified by the manufacturer is 1.2 m rms in static mode, 0.6 rms by using SBAS satellites, 0.5 m CEP (Circular Error Probable, i.e., 50% of measurements) in differential mode (only code), less than 0.5 m + 1 ppm by using post-processed differential correction data and 0.3-0.6 m by using differential correction data from CORS. The low-cost hand-held satellite receiver Thales MobileMapper Pro (named TMMP) allows the determination of the geodetic coordinates of a point and transfer of them to Geografic Information System (GIS) software; it has 12 channels, a position update rate of 1 Hz (1 position s\({}^{-1}\)), a size of \(16.5\times 7.4\times 3.05\) cm and a weight (with batteries) of 227 g, and is powered by two AA batteries. This receiver is equipped with a multipath-resistant internal antenna. An SD board can be inserted into this receiver in order to log a high amount of data. By means of this receiver, it is possible to perform the differential correction only in post-processing. This instrument is able to receive only an L1 signal from GPS and SBAS satellites.