Automated UAV path-planning for high-quality photogrammetric 3D bridge reconstruction

The bridge models reconstructed from unmanned aerial vehicle (UAV) images via photogrammetry are often reported to have quality issues (e.g., high noise, insufficient resolution and precision loss) and thus restrict their application in bridge inspection. To address this problem, this paper proposes a novel Building Information Model (BIM)-based 3D path planning method for improving the quality of photogrammetric bridge models by optimising the UAV flight plan. This method firstly uses a simple BIM model as input and considers inspection and photogrammetry requirements to generate effective UAV viewpoints. Then it adjusts inaccessible UAV viewpoints that are in occupied space or cannot meet the flight safety rules. Finally, a feasible flight trajectory is generated through all valid viewpoints. To evaluate the performance of the proposed method, two prototypes were developed to automate the path planning and on-site image acquisition, respectively, and were tested on a real girder bridge. The results showed that, compared with the common UAV flight plan used in current practice, the proposed method could: (1) generate a more precise bridge model with fewer noise points and higher visual quality to support damage detection; and (2) significantly improve the efficiency of photogrammetric 3D bridge reconstruction with reduced human interventions in image collection and processing.