A digital-twin LiDAR simulator for performance assessment of railway ballast geometry inspections

High-speed railways are increasingly preferred for medium-distance travel, thanks to their efficiency and convenience. However, the growing frequency of services accelerates infrastructure wear, raising inspection and maintenance demands. To address this, autonomous inspection solutions based on LiDAR (Light Detection and Ranging) systems and onboard cameras have recently been proposed, but their testing and deployment remain challenging due to regulatory constraints and the difficulty of accessing representative railway environments. This work presents a LiDAR digital twin that realistically replicates sensor behaviour in real railway track environments. The simulator incorporates CAD (Computer-Aided Design) models of the track vehicle and sensor installation, enabling the assessment of installation-related limitations and sensor field-of-view occlusions. Two commercial sensors, the Livox Avia and Livox HAP, were metrologically calibrated using experimental data acquired on a real railway track. Good agreement between simulated and experimental data was observed, with deviations of only ≃ 2 points/cm 2 in point density and centimetre-level differences in reconstructed ballast geometry. The digital twin was subsequently used to assess the suitability of this technology for ballast geometry measurement at different travel speeds, showing centimetre-order errors for both sensors at speeds of up to 120 km/h.