Path and Intersections: Characterization of Quasi-metrics in Directed Okamura-Seymour Instances

We study the following distance realization problem. Given a quasi-metric D on a set T of terminals, does there exist a directed Okamura-Seymour graph that realizes D as the (directed) shortest-path distance metric on T? We show that, if we are further given the circular ordering of terminals lying on the boundary, then Monge property is a sufficient and necessary condition. This generalizes previous results for undirected Okamura-Seymour instances.