# Feasibility of Using Low-Cost Dual-Frequency GNSS Receivers for Land Surveying
## 4 Conclusions  
The performance of the low-cost dual-frequency u-blox ZED-F9P receiver, connected to the low-cost ANN-MB-00-00 patch antenna, was evaluated. The current price of the hardware is lower than 250 EUR. C/N\({}_{0}\) ratios in such a configuration resulted on average 7 dB Hz lower than those obtained by using geodetic-grade hardware. Still, the low-cost receiver performed well for elevation angles higher than 10\({}^{\circ}\). Low C/N\({}_{0}\) ratios for low  
Figure 11: Positioning error for height (with respect to reference coordinates) of control points measured in two series by using: (**a**) WROC station as reference station; (**b**) NRTK SmartNet; (**c**) u-blox receiver as a base station. Figure 10: Positioning error (with respect to reference coordinates) of control points measured in two series by using: (**a**) WROC station as reference station; (**b**) Network Real-Time Kinematic (NRTK) SmartNet; (**c**) u-blox receiver as a base station. elevation satellites were attributed to the simplified antenna construction, rather than the receiver itself. The C/N\({}_{0}\) differences between GNSS and frequencies were due to varying signal transmission energy. Therefore, multi-GNSS signals acquisition with a low-cost receiver is feasible and has accepted characteristics, but it is worse than that achievable by using a geodetic-grade receiver. In a static relative positioning under open sky conditions, almost 80% of fixed ambiguities were achieved with a 26 km long baseline. For the 50 km long baseline, the average ambiguity fixing rate did not exceed 60%, as the atmospheric error sources prevented ambiguity fixing. The fixing scores were c.a. 10% to 30% lower than those achievable by using a geodetic-grade receiver with baselines of similar lengths [31]. Nevertheless, a centimeter-level accuracy could be achieved in the relative positioning. The positioning accuracy increased with the increasing session length but it decreased with the increasing baseline length. For sessions longer than 1 h, a significant improvement was not observed, neither in the ambiguity fixing rate nor in the horizontal and vertical positioning accuracy. Longer sessions are justified for the absolute positioning using the PPP technique, in which the horizontal and vertical accuracy of few centimeters was achieved after 2.5 h of measurements. In a more challenging surveying environment, i.e., an urban area, an hour-long static relative positioning allowed for achieving a horizontal (2D) and vertical accuracy of 20 and 15 mm, respectively. However, the estimated uncertainties at a 95% confidence level were an order of magnitude smaller. Contrary to baseline solutions, in the absolute positioning, the differences between estimated and known coordinates of control points were much lower than the estimated uncertainties. Differences between the estimated and true coordinates were within the \(\pm\)10 cm range. Horizontal and vertical RMSE resulted in 62 and 56 mm, respectively. A distinct disagreement between accuracy and uncertainty was justified by stochastic models, which varied in the software and are not optimized for measurements performed by a low-cost receiver. Therefore, a limited confidence in the estimated positioning error, i.e., a posteriori standard deviation, is suggested. In the RTK mode, a positioning precision exceeding that provided by the manufacturer, i.e., 1 cm + 1 ppm, was achieved. For a baseline shorter than 0.5 km and geodetic-grade base station, the horizontal error reached 33 mm (RMSE was 20 mm) and the vertical component (Up) was overestimated by 52 mm on average, with the highest error of 73 mm (RMSE was 53 mm). The measurements performed by using two low-cost receivers, of which one as a mobile receiver and the other as a base station, led to further degradation of the positioning precision. Still, the positioning accuracy was high, i.e., the RMSE was 60 and 26 mm for the horizontal and vertical components, respectively.