## 1 Introduction  
Rock masses are typically anisotropic, due to presence of a variety of discontinuities of both primary (bedding planes) and secondary (joints, faults) origin. They present therefore significant variations in the geotechnical and mechanical properties, also in reference to their time-dependent behavior. At this goal, the design in different fields of engineering projects generally considers the use of geotechnical models to characterize a site [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13]. In such models, the rock types are subdivided into units that can be considered homogenous based upon their lithology and technical properties. In this way a 2- or 3-D schematic representation is obtained, aimed at providing a basis for forecasting the behavior of the involved materials, but also at understanding the likely interactions between the ground and the engineering works. In the case of carbonate rock masses, the complexity becomes still higher, due to peculiarity of carbonate rocks, and to the effects of karst processes [14; 15; 16; 17; 18]. Networks consisting of karst conduits and passages are able to significantly change the behavior of the rock mass; as a matter of fact,they are typically the discontinuity sets of greater size and frequency, at the same time showing high pervasiveness throughout the rock mass. This results also in controlling the water flow, which occurs in particular during the most significant rainstorm events. From all these considerations, it appears that karst features strongly complicate any analysis dealing with fractured and karstified carbonate rock masses. Nevertheless, this complication is generally not considered at all in the classical geo-mechanical approaches [19], that are implemented disregarding these important aspects. Karst is known as a particularly difficult to examine environment, so that planning and designing engineering works should be performed with extreme care, including as much as possible the knowledge of the surficial and subterranean karst features, also obtained through direct speleological research and exploration [20; 21; 22; 23]. It therefore appears that, whatever the setting and the lithologies involved, the issue of discontinuity analysis within rock masses is crucial for a correct evaluation of the rock stability, as well as for choosing the most suitable stabilization measures. Standard traditional methods for the geo-mechanical characterization of rock masses are typically time-consuming, with the measurements being confined to some sectors in the rock face, due to difficulties in accessibility [24; 25; 26; 27]. Such limitations result in providing only punctual information about the geo-mechanical setting of the rock mass. The main relevant problem for analysis of rock slopes is therefore logistics, and the possibility to directly approach the rock face: since instability processes mostly affect near vertical to vertical slopes, the only opportunity for operators is making a scanline at the base of the cliff, thus strongly limiting the assessment of the overall rock face. Changes in the properties along the rock face, at different heights, are typically estimated through rough, qualitative approaches. As an alternative, availability by rock-climber geologists allows to fill some gaps, representing however a very difficult, expensive, and time-consuming phase of the survey, in any case able to cover only a few vertical lines. Stereo-photogrammetric techniques are nowadays frequently being used to measure the orientations of discontinuities [28; 29; 30]. Adoption of the basic principles of photogrammetry can in fact result extremely useful in rock mechanics and in the evaluation of rock stability as well. The first attempts in this direction, however, were quite frustrating due to the long time required to precisely outline the discontinuities, and the slowness in their elaboration [31; 32; 33; 34; 35; 36].