Accurate Mapping of Subterranean Structures with Mobile Phones

Accurate mapping of subterranean structures, particularly tunnels, is vital for infrastructure maintenance, safety inspections, and urban planning. Traditional methods such as total stations, LiDAR (Light Detection and Ranging), and Ground-Penetrating Radar (GPR) offer high precision but come with significant financial, logistical, and technical constraints. This paper presents a novel, cost-effective approach to underground structure mapping using the Emlid RX RTK (Real-Time Kinematic) GNSS (Global Navigation Satellite System) rover and the PIX4Dcatch mobile application, leveraging the capabilities of modern smartphones. By integrating GNSS RTK signals, photogrammetry algorithms, and the PIX4D AutoTag technology, the proposed method offers an accessible solution for accurate mapping in areas with limited GNSS signal availability. We demonstrate the feasibility of this method in real-world scenarios, highlighting its potential for enhancing productivity, scalability, and accuracy. This study also addresses the challenges of underground environments, such as poor lighting and sensor navigation, and suggests best practices for mobile phone-based mapping. Our results aim to provide a practical, affordable alternative to traditional tunnel mapping techniques, making them more accessible to users with limited photogrammetric knowledge.