Partly COLREGs-compliant collision avoidance for ASVs using encounter-specific velocity obstacles

A velocity obstacle (VO) based collision avoidance method for autonomous surface vessels operating in restricted and unstructured environments with traffic is considered. We propose a novel VO for enforcing maneuvering compliance with rules 13-15 and 17 in the International Regulations for Preventing Collisions at Sea (COLREGs), where the vessel-to-vessel encounter is first classified w.r.t. the COLREGs, then an encounter-specific domain is assigned to the opposing vessel, and finally a VO for that domain is formulated. The maneuvers of the opposing vessel throughout the encounter is considered when evaluating which side is appropriate to pass the vessel on. This increases robustness to non-compliant behaviour by the opposing vessel. The domain size is determined based on a measure for the available space to maneuver, which ensures an appropriate separation of the vessels in both confined spaces and open waters. Furthermore, collision avoidance with static obstacles from electronic charts is included, where a convex set that is free of static obstacles is constructed to simplify complex geometries, and the boundary of the set is enforced by VOs. The performance of the proposed collision avoidance method is demonstrated through numerical simulation, where it show compliance with COLREGs rules 13-15 and 17. Furthermore, the novel VO shows improved COLREGs compliance compared to another popular COLREGs-specific VO. Copyright (C) 2022 The Authors.