Author(s): Liang Zhang and Mei Hua

Abstract: Unmanned Aerial Vehicle (UAV)-based photogrammetry has emerged as a transformative technology in the field of geomatics, providing an efficient alternative to traditional surveying methods for topographic and structural mapping. This study evaluates the accuracy and operational performance of UAV-based surveying under varying flight altitudes, ground control configurations, and georeferencing schemes, including Real-Time Kinematic (RTK), Post-Processed Kinematic (PPK), and Precise Point Positioning with Ambiguity Resolution (PPP-AR). Experiments were conducted across diverse terrain and structural conditions, using a 20 MP UAV-mounted RGB sensor equipped with RTK/PPK-enabled GNSS systems. High-precision Ground Control Points (GCPs) and independent Check Points (CPs) were established using differential GPS to assess horizontal (RMSE XY) and vertical (RMSE Z) positional accuracy. Results indicated that flight altitude significantly influenced vertical accuracy, with the lowest RMSE values observed at 60-90 m above ground level. Direct georeferencing schemes, particularly RTK and PPP-AR, achieved sub-decimeter vertical and centimeter-level horizontal accuracy, outperforming traditional GCP-only approaches. Moreover, incorporating oblique imagery substantially improved façade reconstruction, edge sharpness, and reprojection error for structural surfaces. Statistical analyses, including regression and permutation ANOVA, validated the significance of altitude and georeferencing configuration on error metrics, achieving R² ? 1.0 when correlating UAV-RTK data with terrestrial LiDAR benchmarks. The findings demonstrate that optimized UAV configurations—combining RTK or PPP-AR positioning, cross-flight geometry, and adequate GCP placement—can deliver mapping precision equivalent to conventional surveying systems while enhancing operational efficiency and safety. Practical recommendations emphasize the adoption of 75-80% image overlap, 60-90 m flight altitudes, and at least eight strategically distributed GCPs for mixed-terrain surveys. The study concludes that UAV-based surveying, when applied under optimized conditions, provides a cost-effective, high-accuracy, and scalable solution for modern topographic, structural, and engineering applications.

Pages: 36-40 | Views: 27 | Downloads: 13

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