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Optimal UAV Image Overlap for Photogrammetric 3D Reconstruction of Bridges

Unmanned Aerial Vehicles (UAVs) and photogrammetry have been widely used to reconstruct a photo-realistic 3D model of physical bridges for documentation of cultural bridges or remote bridge inspection. However, the optimal image overlap for photogrammetric bridge reconstruction that can trade off the model quality and overall mission time has not yet been studied. In this paper, a comparative experiment was conducted on a real girder bridge with three typical overlap configurations being implemented to capture corresponding UAV image sets, based on which bridge models were reconstructed using a commercial photogrammetry software package. Time consumption and the quality of reconstructed bridge models of these three experimental cases were compared and analysed. The results showed that the configuration of 66.7% forward overlap and 50% side overlap is the optimal overlap configuration for the reconstruction of a variety of bridge components, which can result in the minimum number of images while saving the overall mission time for image acquisition and processing. The overlap recommendation may also be applicable to the 3D reconstruction of other types of bridges and buildings with similar structural components.