## 2 Materials and Methods
### Equipment Used
Because the dam was not included in the first flight, being a key element in the simulation, the extracted data were still used to create the Digital Terrain Model. The processing of the data resulting from the second flight was conducted in relation to the first and is exemplified in the following. The most important thing when starting any topographical work is the reconnaissance of the terrain. This was performed in the case of the measurements in this paper, carefully choosing the areas where the six control points were mounted, as they would later be useful for the georeferencing of the resulting orthophoto plane. Three reference points  
Figure 3: Mounting of the targets on the ground. Figure 2: The UAS equipment used for retrieving information (our own source). were installed on the left bank of the Somes River and the other three on the right bank. The areas of the control points were carefully chosen, aiming to choose an open area to ensure the easy visibility of the targets from the drone. The points were materialized by targets printed on a resistant material in the grass and dirt areas (Figure 3) and by spray (in a color that was as obvious as possible) in the shape of an \"L\" in the concrete areas. The markings in a parking lot, in the area where the corner that had to be visible from the drone was marked with an arrow, were also used as reference points. The control point itself was taken either as the center of the square, in the case of targets printed on material or plastic, or in the center of the \"L\"-shaped marking. In practice, it is recommended that these reference marks are not located at a distance greater than 200 m, as this can considerably affect the accuracy of the work. After choosing the mounting areas of the landmarks and their materialization, they determined their coordinates with the help of GNSS equipment. To achieve this step, the static measurement method was used. We started with the first point, which was near the drone's takeoff and landing area. In general, in practice, the most often used static measurement method is the one that offers the highest accuracy. In general, the only impediment this method presents is the need to park in areas as open as possible, offering an unobstructed view of the sky. In the case of the static method, the GNSS equipment was installed in a fixed station, with the observation period being 60 min for each point. After determining the coordinates of the six control points using the static mode, the actual flight was started. The first step in making the flight was approval from the Romanian Civil Aeronautical Authority (AACR). For the aerial images to be of the highest possible quality, the weather conditions were monitored both the evening before and the morning of the flight because too aggressive wind and precipitation can affect the actual flight. The take-off and landing area was chosen in an open area, without trees and vegetation to be able to monitor the drone from the immediate vicinity of the take-off point, which is the same as the landing point. As can be seen in Figure 4, the first flight had a duration of about 14 min over an area of about 20 ha (198,809 m\({}^{2}\)), at 120 m height. Since the greatest clarity was chosen in the construction of the cloud of points, the execution time of the process was a long one, more precisely approximately 60 h. This is due to the number of pixels that this level of clarity produces. Since there were many constructions and excessive vegetation in the area chosen for the study, a so-called cleaning was necessary to have a DEM as clean as possible to create the level curves (Figure 5). Figure 4: Processing of the data obtained using photogrammetric methods. Immediately after this texture was obtained, the software allowed the generation of the inclined model (Figure 6). With the help of the previously generated structures, the DEM (Digital Elevation Model) was drawn. The georeferencing system used was Pulkovo 1942 (58)/Stereo 70.