Novel Sfm-Dlt Method For Metro Tunnel 3d Reconstruction And Visualization

Metro tunnels play a crucial role in urban transportation. However, with growing tunnel operation periods, defects, and large deformations appearing, these are influencing tunnel structural performance and threatening public safety. Three-dimensional (3D) tunnel reconstruction is an effective way to highlight tunnel conditions and provide a basis for engineering management and maintenance. However, the current methods of tunnel 3D reconstruction do not sufficiently combine the qualitative and quantitative characteristics of tunnel states. In this study, a novel method for metro tunnel 3D reconstruction based on structure from motion (SfM) and direct linear transformation (DLT) is proposed. The dimensionless 3D reconstruction point cloud acquired through the SfM method showcases the qualitative characteristics (such as leakage and pipelines) of the tunnel state. The close-range photogrammetry DLT method provides scale information missing from the SfM method and quantitative characteristics (such as profile deformation) of the tunnel state. The SfM-DLT method was tested in a Shanghai metro tunnel, and proved to be feasible and promising for future tunnel inspections.