Camera-based measurement for close-distance relative vessel positioning

This paper presents a technique for quickly and accurately measuring the position and heading of a vessel for relative vessel positioning at close distances to a target. To this end, we propose a measurement system that consists of camera units and landmarks. This system calculates the position and heading based on the distance and angle between the camera units on the vessel's side and landmarks on the target's side. Cameras with a high frame rate, wide sensing range, and excellent angular resolution are employed as sensors for measuring the position and heading, rather than GPS, radar, or lasers. A pattern-matching method based on the intensity gradient is developed in order to provide the proposed system with a fast response time. Correction methods for the distance measured by the camera unit and installation errors are also proposed to improve the accuracy of the measurement. We evaluated the accuracy of the proposed system using several positional relations between the camera units and landmarks. We demonstrate that the proposed system can accurately measure the position and heading of a vessel, despite the vessel's roll and pitch motion as a result of waves.