## 3 Discussion
### Application for Positioning Accuracy  
Mobile Mapping System (MMS) [118; 119] presents an additional area of research; then, these points were positioned in NRTK mode. MMS acquisitions were experimented with, enabling the retrieval of terrain morphology, building conditions, footpaths, and street pathways. The initial phase involved surveying numerous benchmark control points in NRTK mode once these were established across the site using static GNSS mode. During the survey, the Leica CS-10 receiver obtained real-time corrections from the GNSS CORS network. The subsequent phase involved an EGNOS-mode survey of the tree species. Figure 6: On the left panel: a CSK Single-Look Complex image of the dam-reservoir system. Superimposed the positions of the GNSS receivers (red points). On the right panels: PS-InSAR and GNSS estimations (red dots in the upper right panel and black dots in the lower right panel) of the horizontal total displacements orthogonal to the dam temporal. Superimposed in both right panels, to facilitate the phenomenon comprehension, are a sinusoidal interpolation curve and a confidence band twice the standard deviation between interpolated and in situ values. Adapted from [113]. Similar to the NRTK survey, numerous benchmarks were initially established in static mode using GPS. These measurements were conducted using a PDA GeoXH Trimble equipped with an optional Zephyr external antenna. In the final phase, the survey was executed using Topcon's IP-S2 MMS. The Spatial Factory software supplied the point cloud gathered by the laser scanner during the survey campaign, the vehicle's plotted trajectory, and spherical images from a 360\({}^{\circ}\) camera. For more details, please refer to paper [120]. A new approach was developed to optimise the sampling area across an old-growth forest using geomatics techniques such as GNSS, UAV-borne laser scanning, and radial surveying. This enabled the estimation of structural attributes with tolerable error [121]. The plot size was estimated by visualising the semivariogram of a canopy height model (CHM) by UAV laser scanning. The tree heights estimated by UAV laser scanning resulted in a strong correlation with the heights of the trees measured in situ. However, the positioning of several trees required the use of both GNSS and total station geomatics surveys. Due to the tree heights hindering the GNSS signal transmission, only the GLONASS satellite constellation (which showed the highest dilution of precision during the survey) was used to fix the solution, while the GPS satellite constellation was used to augment position accuracy (PDOP-5\(-\)10) (Figure 7). As a final highlight of the _UNIPA GNSS CORS_ network applications, one aspect is analysed that plays a very interesting role in the accuracy of the network achieved during surveys. In the paper [122], the advantage of using the multi-GNSS PPP technique in static mode was analysed. Specifically, the main aim of the study was to determine the contribution of the new Galileo satellite system when it is used in addition to those already well-established, such as Navistar GPS and GLONASS. For this purpose, the open-source RTKLib software (version 2.4.2 p13) was used; the dataset available in this work was augmented with satellite precise orbits and clocks from _Collete Localization Satellites_ (CLS) analysis centres for the International GNSS Service (IGS) and _Centre National d'Etudes Spatiales_ (CNES). Specifically, the well-known models _Iono-free_ (ionospheric errors) and _GOT-4.7_ (tidal effects) were used. Two different tropospheric models were also tested: _Estimate Zeenith Teospheric Delay_ (ZTD) and _Saastamoinen_ models. Two datasets of 31 and 10 days from a GNSS CORS station located in Palermo and from a benchmark neighbouring the CORS were used and then managed by open-source software for geomatics applications.