## 3 Discussion
### Application for Positioning Accuracy
Considering the network solutions, the best standard deviation of the residuals was obtained on average by applying the VRS (\(\approx\)5.1 mm), then the FKP (\(\approx\)6.7 mm), and the Near (\(\approx\)7.4 mm). Also, an evaluation of the accuracy of different GNSS geodetic receivers was made, with accuracy used for mapping and guidance of agricultural machines in precision farming [124]. _Quantum GPS Logger V2_, _Thales MobileMapper Pro_, _Stonex S5_, and _Stonex S7-G_ were used in this application. Several tests were carried out, including the evaluation of the distance of some points with respect to the NRTK trajectory; the use of differential correction data and an external antenna, demonstrating that the use of an external antenna always improves positioning accuracy; and the satellite receiver, which showed the worst positioning accuracy; the low-cost receiver surprisingly showed a low positioning error (\(\approx\)0.5 m), used in precision farming. The evaluation of the coordinates from a GNSS survey (static mode, PPP, or Network Real Time Kinematic) has been investigated in numerous technical and scientific papers. Many of these have been carried out to relate Network Real Time Kinematic (NRTK), PPP, and static modes solutions, assuming the previous in the literature as the true or most reasonable result. In the article [125], the above-mentioned GNSS surveying methods were compared in pairs, using some benchmark points, to check the congruence of their solutions. The static and NRTK solutions refer to a local GNSS CORS network's investigation. The NRTK positioning was obtained by different methods (NEA, FKP, and VRS), and the PPP solution was expected by using two different open-source softwares (CSRS-PPP version 2 and RTKLIB version 2.4.2 p13). To test the solutions, a statistical approach was used to check whether the distribution frequencies of the coordinate residuals belong to the normal distribution for all examined pairs. In this case study, the hypothesis of a normal distribution was confirmed, in particular for the NRTK vs. static pair, which seems to achieve the greatest congruence, while pairs involving the PPP approach obtained better congruence with the CSRS than using the RTKLIB (Figure 9). Figure 9: On the left panel, Sicily network benchmarks, IGM95 network benchmarks, UNIPA GNSS CORSs, and local benchmarks are represented with white squares, white triangles, black triangles, and white circles, respectively. Superimposed a 20 km buffer from the GNSS CORS. Reference system: UTM-WGS84 33N (ETRF2000-RDN2008)-EPSG6708. Lower right panel: an example of a spider graph, pre- and post-removal of the outliers (dashed and continuous lines, respectively), for different PPP and NRTK vs. static solutions, with tested pairs reported on the upper right scheme. Adapted from [125]. Finally, Ref. [126], the positional accuracies of some cadastral marks were analysed and compared with official maps produced by Google Earth Maps, local cartography, and the cadastral government department (Figure 10). The results showed centimetric accuracy obtained by the GNSS NRTK survey, both in the planimetric and altimetric components.