Below-Deck Personnel Inertial Positioning System: For enclosed, signal-shielded ship compartments, it combines inertial navigation and gait algorithms for continuous tracking. It supports track replay, geofence alerts, personnel and access statistics, and BIM visualization. The 200 g wearable or portable terminal provides 2–3 m accuracy, 1-second updates, IP68 protection, multimode communications and offline data recovery. Cable-free deployment supports routine monitoring and emergency rescue.