Mobile Mapping Systems for Road Tunnel Inspection: Influence of Acquisition Speed and Control Point Configuration on Geometric Reliability

Mobile Mapping Systems (MMS) are increasingly adopted for transport infrastructure inspection, where reliable characterization of global and local geometry is essential. This is critical in GNSS-denied environments such as road tunnels, where trajectory estimation relies on inertial navigation and drift degrades geometric accuracy. This study investigates the influence of acquisition speed and ground control point (GCP) configuration on trajectory accuracy and geometric consistency in a 2.3 km road tunnel. MMS data were acquired at 15, 30, and 50 km/h and processed under progressively denser, uniformly distributed GCP configurations, from unconstrained to fully constrained solutions. Post-processed forward–backward smoothed GNSS/INS trajectories were validated against a topographic control network, and cross-sectional geometry against terrestrial laser scanning (TLS). Without external constraints, planimetric errors at independent check points reached 16.5 m and global deformation reached 0.46% at low speed. Ground control markedly reduced trajectory errors, depending on both control density and acquisition speed. In contrast, locally registered cross-sections showed millimeter-level consistency with TLS in all configurations: median discrepancies of 4–5 mm, with 75–82% of values below 10 mm. Local cross-sectional shape is therefore preserved despite substantial global drift, supporting MMS for shape-based tunnel inspection, while adequate ground control remains necessary for absolute georeferencing.