## Methods  
### Surveying Methods  
#### 2.1.1 Terrestrial Laser Scanning  
Terrestrial Laser Scanning (TLS) can be considered as a technology suitable for non-contact measurement of spatial coordinates, 3D modeling, and visualization of complex underground structures ([18] and others). During the last years, terrestrial laser scanning has been widely used for the detailed survey of cave spaces and the study of cave morphology ([19; 20; 21; 22; 23; 24; 25; 26; 27; 28] and others). The high speed of scanning, accuracy, higher productivity versus common geodetic methods (such as selective measurement of individual points by total stations), significant shortening of fieldwork, and automatic data processing into digital models make this technology almost irreplaceable in rapid speleological mapping. Another important advantage is the use of own source of a laser beam, which ensures hassle-free surveying in poorly illuminated, or even not illuminated underground spaces [29]. Additionally, simpler methods exploiting laser distance measurers were used for capturing cave ceiling morphology [30], but the level of detail recorded does not reach the capabilities of TLS. A compact all-in-one full panoramic pulse terrestrial laser scanner Leica ScanStation C10 was used for the survey, based on the points of the original survey net (Figure 4). The scanner is equipped with a scanning system based on the Time-of-Flight system (ToF), measuring the given distance based on the transit time of the emitted signal. TLS systems emit intense monochromatic, coherent, and high-directional radiation [31]. Since the laser scanner used in this work is a long-range laser scanner with the mean error in position 6 mm and mean error of distance measurement 4 mm, we used it as the main instrument for mapping and subsequent 3D modeling of the Ochtina Aragonite Cave. During the presented survey, suitable survey stations were chosen after the terrain reconnaissance, while points of the geodetic control monument in the concrete tourist path were used as initial surveying points. In order to eliminate measurement errors related to the centering of an instrument over fixed survey points, we decided to use the method of dependent centering (the surveying target for scanner orientation is inserted directly into the centering plate instead of the laser scanner and vice  
Figure 4: Leica ScanStation C10 during the survey and its technical specification. versa). The highly reflective 6\" High Definition Surveying (HDS) targets supplied by the manufacturer were used for registration of scans in the given space. This is the most common registration approach. The coordinates of the centers can be estimated from a number of phase returns covering the surface of the target--target centroiding [32]. Cavities, ponds, tourist path, as well as aragonite decoration, were scanned with high resolution and detail. Overall, more than 121 million points using 54 survey stations placed over survey control points monumented in the concrete tourist path were measured during the laser scanning. The horizontal and vertical resolution on the scanned surface of \(20\times 20\) mm was achieved (Figure 5). The survey was realized in the binding national coordinate system using 10 survey stations located near the cave entrance and in the connecting tunnel. The spatial coordinates of morphological structures were determined in the Slovak national coordinate system and vertical datum by the principle of direct georeferencing [33]. For the initial processing and editing of the scanned data, a professional 3D point cloud processing software Leica Cyclone version 7.3 (Leica Geosystems AG, Heerbrugg, Switzerland, 2011) was used.