3D tunnel reconstruction and visualization through multi-smartphone photogrammetry

Tunnel documentation and inspection are crucial for ensuring public safety. To provide a useful tool in 3D tunnel reconstruction for engineers, we propose a novel multi-smartphone measurement (MSM) system for reconstructing and visualizing 3D tunnel models. This innovative system boasts user-friendly operation, streamlined data capture, and cost-effectiveness as its defining attributes. The system consists of eight smartphones, a controller, a backpack, and software. Different shooting strategies with various overlaps along the longitudinal and circumferential directions are investigated in a pedestrian tunnel. A uniform overlap rate along the circumferential direction can be achieved in the MSM system. By comparing the results with total station measurements, the evaluation of the system's performance is carried out and assessed from point density and point distance error. The results show that the average absolute point distance errors of the system are less than 0.3 cm under a high overlap and that an overlap along both circumferential and longitudinal directions close to or higher than 50% is recommended for 3D tunnel reconstruction. With the features of easy handling, efficient recording, and low pricing, the MSM system has the potential to provide a useful tool for tunnel visualization and documentation.