## 5 Discussion  
The two case studies presented in this paper regard a very common situation in long stretches of the Italian coastlines (high cliffs interested by rockfalls and slope failures, threatening tourist sites below) and in wide areas of the country where underground voids are present, of both natural ( karst caves) or artificial (man-made cavities) origin. Rock failures and sinkholes are definitely among the most significant geological hazards in a fragile territory as Italy. Very often, studying sites affected by these processes has several difficulties related to logistics (overhanging walls, danger from detachment of rocks, etc.) that make it more complicated to carry out a thorough analysis, aimed at defining the kinematics of possible slope movements, at performing the most proper stability analysis, and at designing the related stabilization works. The traditional approaches to assess the quality of rock masses, as the main available geomechanical classification, proposed since many decades in the international literature [109, 110, 111, 112, 113, 114, 115, 116, 117], still appear to be important but present many problems when applied in logistically difficult situations. The fieldwork campaign, necessary for implementation of these classifications, is expensive and time-consuming, and typically does not allow to entirely cover the area under study. Further, it requires somewhat repetitive actions, often resulting in the possibility of having incorrect data. To effectively reach the goal to evaluate the stability conditions in these situations through detailed analyses, based upon a sound amount of reliable data, the use of remote techniques may play a crucial role in the identification of the discontinuity sets characterizing the rock mass, but need to be carefully planned and always integrated by the necessary geo-structural and geomechanical checks on site [12, 118]. We described implementation and integration of techniques used for the above aims, and applied them to study two sites where terrestrial laser scanner and unmanned aerial vehicles were used individually or in combination to build a cloud point from which to develop a semi-automatic extraction of discontinuity data to use for stability analyses. At Santa Caterina cliff, a combination of the two techniques was necessary to ensure a complete coverage of the area under study, at the same time obtaining high quality photographs of the cliff. In the case of Castellana, a variety of scan  
Figure 15: Stereoplot showing the comparison among the data from geo-structural analysis from point cloud and direct acquisition from standard geomechanical survey. positions to occupy (thanks to the tourist pathways), and good light coming from the outside through the natural opening, permitted to use TLS only. Through implementation of the two techniques, further integrated by other experience from the literature, and from many years of direct expertise from the authors, we were able to identify the main advantages of these approaches, but also some drawbacks that are worthy of further investigation in the future. As regards the LST technique, a very positive feature is represented by the high accuracy of the survey (in our case <5 mm, by using Riegl [2400]), together with the relative velocity in elaboration of the point cloud. On the other hand, drawbacks are the chromatic outcome of photographs, due to the technique used (spherical panchromatic pictures), and the common difficulty in moving around the object to be surveyed, due to site logistics. This latter problem might potentially result in \"loosing\" some discontinuity sets, depending upon the relative geometries among their attitudes and location of the scan positions. The two drawbacks above can be solved by using UAV techniques: orthophotos are in this case of good chromatic quality, and there is no problem in moving around the object, which allows to survey the discontinuity plans always with a frontal view.