# A Quantitative Evaluation of UAV Flight Parameters for SfM-Based 3D Reconstruction of Buildings
## 2 Literature Review  
### Acquisition of Building Shape Information  
Building geometry information is used as core data throughout the entire building lifecycle management process, including structural stability checks, material deterioration assessments, identification of exterior damage and defects, and maintenance plan development [14]. In particular, damage frequently occurs due to long-term use, environmental changes, and material deterioration, and accurate shape information is essential for effective management [11]. Traditional surveying methods include high-altitude work, photography, and aerial photography. These methods have issues such as difficulty in accessing high-rise exterior walls, safety concerns in operating equipment, and reduced economic efficiency due to long working hours [15].  
Various 3D surveying and restoration technologies can be applied to collect building shape information. These include 3D scanning, photogrammetry, and 360-degree camera photography, each with its own advantages and limitations. First, 3D scanning is a technology that uses sensors such as laser scanners (LiDAR) or structured light to acquire high-precision, high-density point cloud data [16]. It is widely used in cultural heritage restoration, industrial plant measurement, and precise architectural structure measurement [17]. This method ensures high precision but requires expensive equipment, installation, and operation personnel, and faces measurement constraints in accessing high-rise exteriors [18]. Photogrammetry is a technology that analyzes multiple overlapping photographs to restore 3D information [19]. It uses general cameras, resulting in low equipment costs and flexibility for various scales and shapes of objects. Photogrammetry has already been applied in pilot studies for small-scale buildings or civil engineering structures, and it is able to easily obtain images even in locations difficult to access using UAVs [20; 21]. However, when applied to large-scale structures, issues such as securing shooting points and blind spots arise, and image quality management is crucial for obtaining high-precision and high-density point clouds. Additionally, a well-planned shooting path is necessary to cover complex shapes. In this context, 360-degree cameras can record the entire surrounding environment in a single shot, making them useful for virtual tours and real estate presentations [22]. However, due to resolution limitations, they often lack sufficient detail and struggle to reproduce high-precision 3D data, making them unsuitable for precise structural analysis or defect detection [23].  
An approach that simultaneously achieves measurement accuracy, efficiency, and minimization of blind spots by comparing and integrating these individual methodologies is necessary for rapid and precise modeling of building exteriors. Considering the significant cost and access limitations of 3D scanning for frequent, large-scale assessments and the precision drawbacks of 360-degree cameras for detailed analysis, photogrammetry emerges as a promising candidate. Therefore, when photogrammetry, which offers cost-effectiveness and ease of use, is combined with UAV-based image acquisition, significantly improved accessibility and data collection capabilities compared to existing methods can be expected.