Low-cost support visualization of bridge structures using smartphone LiDAR and head mounted Augmented Reality (AR)
Authors: Uzor Stephen , Sotoudeh Saeed , Tosti Fabio 
Published: March 2024

Continual monitoring of civil structures (e.g., bridges) is essential to maintenance and ensuring safety and integrity. Non-destructive techniques, for instance, laser scanning, acoustics, and Ground Penetrating Radar (GPR) have been used in the past to study both the external and internal physical dimensions of objects and structures [1]. Light Detection and Ranging (LiDAR) technology has also been used in infrastructure monitoring to capture structural 3D information and to detect displacements in surfaces with millimeter accuracy [2]. Some other technologies, such as the Ground-Based Interferometric Radar (GBIR), suffer from precise target detection when monitoring objects and require installation of dedicated reflectors. Scanning structures using these existing state-of-the-art technologies can be expensive and time-consuming. Recently, visualization technologies such as Augmented Reality (AR) have been utilized with GBIR to solve target location uncertainties by making the radar&#8217;s beam of radiation interact with the investigated structure [3].This work proposes the use of head-mounted Augmented Reality (AR) to visualize and support the monitoring of bridge structures. First, to overcome limitations of the HoloLens depth sensing technology, we used smartphone-based LiDAR (Apple iPhone 14 Pro) to capture and export a 3D model of the shape of the structure of interest. We then imported this model into the HoloLens application so that it could be overlaid and adjusted to match the physical bridge structure. Second, a digital component model was aligned with the position and orientation of the antenna. The beam of radiation is estimated in the visualization application using the method described in our previous work [3]; then, it is displayed as a frustrum determined by an equation according to this method. Since this method does not rely on real-time LiDAR or depth mapping, we are able to visualize the projected beam of radiation beyond the usual range limitations of up to 7 meters. Furthermore, this method can be used effectively in outdoor locations, which can be challenging for infrared-based depth mapping technology.The system can provide a relatively low-cost structural monitoring and assessment solution, which can allow researchers and surveyors to accurately visualize survey areas of interest and inform the decision-making process regarding maintenance of crucial civil structures.&#160;Acknowledgments: Sincere thanks to the following for their support: Lord Faringdon Charitable Trust, The Schroder Foundation, Cazenove Charitable Trust, Ernest Cook Trust, Sir Henry Keswick, Ian Bond, P. F. Charitable Trust, Prospect Investment Management Limited, The Adrian Swire Charitable Trust, The John Swire 1989 Charitable Trust, The Sackler Trust, The Tanlaw Foundation, and The Wyfold Charitable Trust.&#160;References[1] Alani A. et al., Non-destructive assessment of a historic masonry arch bridge using ground penetrating radar and 3D laser scanner. IMEKO International Conference on Metrology for Archaeology and Cultural Heritage Lecce, Italy, October 23-25, 2017.[2] Lee, J et al., Long-term displacement measurement of bridges using a LiDAR system. Struct Control Health Monit. 2019; 26:e2428.[3] Sotoudeh, S. et al. "A study into the integration of AR-based data collection and multi-dimensional signal processing methods for GB-SAR target detection." Second International Conference on Geographic Information and Remote Sensing Technology (GIRST 2023). Vol. 12797. SPIE, 2023.