  The agents within a multi-agent system (MAS) operating in marine environments
often need to utilize task payloads and avoid collisions in coordination,
necessitating adherence to a set of relative-pose constraints, which may
include field-of-view, line-of-sight, collision-avoidance, and range
constraints. A nominal controller designed for reference tracking may not
guarantee the marine MAS stays safe w.r.t. these constraints. To modify the
nominal input as one that enforces safety, we introduce a framework to
systematically encode the relative-pose constraints as nonsmooth control
barrier functions (NCBFs) and combine them as a single NCBF using Boolean
composition, which enables a simplified verification process compared to using
the NCBFs individually. While other relative-pose constraint functions have
explicit derivatives, the challenging line-of-sight constraint is encoded with
the minimum distance function between the line-of-sight set and other agents,
whose derivative is not explicit. Hence, existing safe control design methods
that consider composite NCBFs cannot be applied. To address this challenge, we
propose a novel quadratic program formulation based on the dual of the minimum
distance problem and develop a new theory to ensure the resulting control input
guarantees constraint satisfaction. Lastly, we validate the effectiveness of
our proposed framework on a simulated large-scale marine MAS and a real-world
marine MAS comprising one Unmanned Surface Vehicle and two Unmanned Underwater
Vehicles.
