## 4 Case Studies
### Castellana Caves
Several different resolution scans were produced at each survey station, and the overall amount of data was processed through dedicated software. In order to obtain frontal scans of the discontinuity sets, seven out of the 12 scans within the _Grave_ were taken with the laser inclined 90\({}^{\circ}\) with respect to the vertical axis, by means of the \"Tilt Mounting\" tool. The resulting point cloud was of high definition, also thanks to presence in the cave of boardwalks and ramps for the tourist visits, that made it possible to locate the scanner at many points. In this way, all the scans were produced at distance not greater than 30-40 m from the rock walls. Further, the opening of the _Grave_ allowed natural lighting inside the cave, thus obtaining good chromatic  
Figure 10: Real numerical model of the point cloud. The blue vertical line provides the height of the cavern. pictures. At this regard, the survey was carried out during early morning and late afternoon, to avoid the direct arrival of sun rays during the acquisition phase of the photographs. Overall, the survey required two working days: on the first day, the 10 cylinder targets were surveyed by GPS and total station, and the surface scans outside the cave were performed (16 scans over eight scan-positions), for a total time of 6 h; on the second day, 26 scans within the cavern were carried out in 8 h, also surveying by total station the 15 flat targets. The elaboration process, consisting of linking and roto-translating the different point clouds, and in optimization by cleaning the dataset, produced the high-detail solid surface (mesh) to represent the geometry of the _Grave_ (Figure 11). The geological-structural analysis of the _Grave_ was performed by direct measurement of the discontinuity sets in the point cloud through specific software (RiscanPro, Cyclone, Cyclone 3 DR, Cloud Compare) able to analyze its attributes, with particular regard to the values (described by three spatial coordinates) of the normals associated to each point within the cloud. The semi-automatic procedure started from identification of sectors showing similar orientation, through analysis of the normals. The same procedure described in the Santa Caterina cliff case study was then followed, assigning a new attribute to the point cloud, computed by associating the attitude (dip/dip direction) to the value of the normal at each point. In this semi-automatic method, the phases of identification, computation, and conversion of the normals in geological datum is preceded by a process of manual selection (control and validation) of the elements to be modelled. This represents a very important point, allowing the operator through his/her expertise to fully control the output. The planes identified were portrayed in stereographic projections, by ranking the data in sets of discontinuities. The great majority of the attitudes are high dipping; for this reason, variations in discontinuity polarity, due to the possibility to encounter undulated planes, were considered. Three main sets of discontinuities, plus the bedding, were identified from the 113 discontinuity measurements (Table 3). The graphic representation of the main discontinuity planes identified directly from the point cloud is shown in Figure 12. The most frequent and developed sets of tectonic origin (namely, K1 and K2) are well identified by the statistical analysis carried out on the point cloud, as shown by the histogram presented in Figure 13.  
Figure 11: RGB point cloud of the Grave. To the right, height of the bust dedicated to Prof. [PERSON] (discoverer of the cave system in 1938) provides an indication of scale. Data obtained through the above described semi-automatic procedure were checked through traditional survey, by operating two scanlines along the vertical walls of the _Grave_,  
Figure 12: Representation of the main discontinuity planes identified directly from the point cloud:  
(a) all sets; (b) bedding; (c) K1; (d) K2.