## 3 Results and Discussion  
During the expedition, all groups of objects were studied. **Photogrammetry of Large Object**: As a result of the mountainous terrain and subtropical vegetation, UAVs were used in order to obtain accurate plans of the settlements and to study the design of large temple complexes and fortresses. This required us to develop photogrammetry methods for this purpose. The photogrammetry of such objects is divided into two tasks:  
* receiving an orthophotomap of an object;
* obtaining a detailed 3D model. The orthophotomap of the Markul settlement was obtained by our expedition in 2019, which made it possible to map the territory and to create a digital elevation model (DEM) (Figure 4) [12]. The method for obtaining an orthophotomap of an archaeological object is very similar that of a usual geodetic survey using a UAV, which involves shooting at a 90\({}^{\circ}\) angle to the horizon [13]. We found that shooting is the most effective when:  
* the flight height of the drone is approximately 15 m;
* the overlap of adjacent frames is 60-80%;
* the camera is tilted 90\({}^{\circ}\) to the horizon. This photogrammetry method was tested over the remains of the Godlik fortress (Lazarevsky district of Sochi, Figure 2, No.1). The drone used was a DJI Mavic Mini with a 12 Mpx camera. The flight height was 25 m due to the tall trees and buildings in the area of the fortress. The camera was set for automatic shooting at an interval of 2 s, and the trajectory and flight speed were selected to provide the necessary overlap of frames and create, if possible, a perpendicular grid of images. The tilt angle of the camera was set to 90\({}^{\circ}\) to the horizon (Figure 5). Figure 4: Digital elevation model (DEM) of the Markul settlement. 1—excavations on the southwest-ern slope; 2—south Alakhash-Abaa tower; 3—temple; 4—a fragment of the wall; 5—northern tower. Figure 5: The position of the cameras when shooting the Godlik fortress from the UAV. Processing the shots showed that:  
* in vertical shooting, upright details, such as walls, etc., are not partially or fully shot, and the texture is heavily distorted or smeared on the final picture;
* even in the absence of vegetation (shooting was carried out in February 2021), shooting vertically down through the crown of trees and bushes does not allow the surface of the earth, the fragments of walls, or fortress towers to be captured. In this scenario, it is nearly impossible to automatically determine the relevant points, which leads to the situation in which a series of pictures with trees are not recognized and deleted. When there are readable objects (the remains of a fortress wall, buildings, roads, open spaces with grass) and tree crowns, the pictures are easily recognized. As a result, the fortress was only readable in areas that were free from vegetation in the processed orthophotomap, which made it impossible to build an entire plan of the fortification (Figure 6). Moreover, its contours were better estimated in the DEM (Figure 7). On the basis of the analysis, it was decided to attempt tilted aerial photography to avoid the distortion of vertical details and to capture the earth's surface under the crowns of trees. In order to avoid distortions, the shooting angle was adjusted to 60\({}^{\circ}\). This technique was tested in the study of Pitiunt fortress (Pitsunda, Republic of Abkhazia, (Figure 2, No. 2) [14]. The fortress is located on a flat terrain and occupies an area of 150 \(\times\) 230 m. The southern and western parts of the fortress wall and the inner territory of the fortress were free from dense vegetation, while the northern and eastern parts were heavily overgrown and in some places are in a swamp. The shooting interval was selected as 2 s, the flight altitude was 25 m due to the cypress trees inside the fortress, and the flight speed was selected to ensure a frame overlap of 60-80%.