# Evaluation of Low-Cost GNSS Receiver under Demanding Conditions in RTK Network Mode
## 1 Introduction
This receiver, offering wide usability, has become the subject of research in the field of e.g., positioning accuracy. [PERSON] et al. [23] tested the ZED-F9P receiver for positioning accuracy using different methods. In static mode, they obtained RMSE (root mean square error) values of 11, 17 and 15 mm for north, east and up components, respectively, based on differences from reference data. In contrast, in RTK mode, they found that the manufacturer's parameters were not met and were 20 mm and 53 mm (both RMSE) for horizontal and vertical components, respectively, for a baseline shorter than 0.5 km. In addition, it was noted that the main source of height error was the use of low-cost antennas. Further tests for this receiver were performed by [PERSON] et al. [24], who used low-cost antennas from various manufacturers to determine position using the static method. Their results allowed them to conclude that low-cost instruments give a coordinate accuracy of a few millimeters, but their precision is four times worse than that of geodetic receivers (based on adjustment of the established geodetic network). A detailed study on the influence of a patch antenna was carried out by [PERSON] et al. [25] by comparing it with geodetic-grade antennas, with and without consideration of antenna-relative calibrations. A critical component of the low-cost receivers is the patch antenna, due to the noticeable degradation in positioning accuracy. For this reason, they have been tested using high-precision geodetic antennas. Thus, [PERSON] et al. [26] verified the accuracy of single-frequency u-blox receivers. The results obtained were comparable to geodetic receivers--not exceeding 0.005 m (2\(\sigma\)) in all components (for a baseline shorter than 0.5 km) and 0.02 m (for up to 18 km long baseline). Even better results were obtained by [PERSON] et al. [27], obtaining RMSEs below 2 mm and about 5 mm for the horizontal (Hz) and vertical (V) components, respectively, based on 1 h static observations. Moreover, they estimated the accuracy of the real-time solution as 4 mm (Hz) and 8 mm (V) RMSE. A similar RTK mode study was performed by [PERSON] et al. [28], comparing the ZED-F9P results with a professional geodetic receiver. They obtained a 3D position standard deviation value of 7 mm, which they considered excellent for low-cost GNSS equipment compared to a value of 13 mm obtained with a high-end receiver. It is worth noting that the tests mentioned above were usually conducted under favorable field conditions, i.e., with a large number of available satellites and an open horizon. However, terrain obstacles are a significant handicap in many practical cases, so it seems reasonable to perform tests under such conditions. The tests carried out in this thesis take into account different terrain situations, ranging from an open-sky environment, through a horizon obscured from different directions, to the case of an urban canyon. Furthermore, in testing the accuracy of the devices, it is crucial to provide reliable reference values. Most comparisons utilize results obtained with different GNSS receivers, equipped with various antennas (patch and geodetic), using other positioning methods. In this paper, satellite observations are compared with total station measurements, which provide higher accuracy and are less dependent on random factors such as satellite availability or multipath effect. The motivation for undertaking the research was to verify the accuracy of a low-cost dual-frequency GNSS receiver operating in RTK mode in relation to high-precision observations. An essential element of our work was to create diverse field conditions in which low-cost receivers can be used, such as during vehicle positioning. Furthermore, we conducted tests by introducing a mid-cost solution, expecting worse results for low-cost receivers. A high-precision geodetic antenna was combined with a low-cost receiver.