## 2 Materials and Methods
### UAV-Based Photogrammetry: Capabilities and Limitations  
In recent years, a significant increase has been observed across various industries in the use of measurement techniques based on photogrammetry--a scientific and technical discipline that reconstructs real-world dimensions, shapes, and spatial relationships of objects through the analysis of image sequences captured from multiple viewpoints. Particularly notable is the rapid development of close-range photogrammetry using UAV, equipped with specialized cameras that minimize optical distortions, such as chromatic aberration (Figure 2). This trend is clearly reflected in the mining sector as well. A comprehensive literature review by [PERSON] and [PERSON] (2018) analyzed 113 scientific publications over the past 12 years, documenting the systematic increase in UAV applications across key mining activities. These include mine surveying and inventory (application in surveying mines), design and monitoring of drilling and blasting operations, mine safety and risk management, ground subsidence monitoring, rock slope stability analysis and monitoring, detection of underground coal fires, and erosion detection. An optimal--though not exclusive--solution for blasting design is the use of aerial photogrammetry. This technique, by virtue of its mobile measurement platform, inherently eliminates issues related to limited perspective or access typical of ground-based scanning. Figure 3 illustrates an example flight path planned for UAV scanning of a selected production bench. Figure 1: Example visualization of a point cloud acquired using a 3D laser scanner. Key rules to keep in mind before flying a bench [58] are as follows:  
* At least two-thirds of the photos should be taken with the camera pointing straight down (nadir images). * Capture images along flight paths with 70-80% overlap. * Effective results have been reported at flight altitudes of 75 ft (23 m), 150 ft (46 m), and 250 ft (76 m). * Always overshoot the mapping area by at least 20 ft (6 m) to avoid stitching or reconstruction issues at the edges. * Fly the UAV forward with the camera tilted \(5^{\circ}\) forward; when beginning the next pass, rotate the UAV instead of flying backward. Figure 3: Example flight trajectory designed for the UAV. Figure 2: UAV conducting a flight over a designated section of the excavation site. As previously mentioned, the use of stationary terrestrial laser scanners for single or series-based surveys may present operational limitations due to structural and functional constraints of the device. These limitations often result in extended measurement durations, increasing the risk of incomplete geometric data acquisition, which in turn can compromise the accuracy of blast design. UAV deployment significantly mitigates problems related to instrument positioning and scanning geometry, thereby improving overall operational efficiency. Photogrammetric techniques based on UAV imagery are typically more functional and offer potentially higher spatial resolution. However, UAV-based measurements also come with certain technical and regulatory limitations. These include high sensitivity to weather conditions (e.g., wind, rain, and fog), limited operational time due to battery capacity, the requirement to maintain stable data transmission with the ground control station, and--under most regulations--the necessity of maintaining visual line of sight (VLOS). Additionally, photogrammetric data quality can be affected by lighting conditions and surface characteristics--low contrast, homogeneous textures, or reflective surfaces may degrade the final 3D model, requiring supplementary ground-based measurements for validation. It should be noted that stationary terrestrial laser scanning does not require formal operator licensing. In contrast, UAV operations in public airspace are legally regulated. Operators must obtain UAV pilot certification, which includes theoretical and practical training followed by an official examination.