The multiple location of transfer points

In this paper, we investigate the location of several transfer points to serve as collector points for customers who need the services of a facility. For example, demand for emergency services by patients is generated at a set of demand points that need the services of a central facility ( such as a hospital). Patients are transferred to a helicopter pad ( transfer point) at normal speed, and from there they are transferred to the facility at increased speed. The general model involves the location of multiple transfer points and one facility. Locating one transfer point when the set of demand points and the location of the facility are known was investigated in a previous paper by the authors. In this paper, we apply the results of that paper to solve the problem when the location of the facility is known. Both minisum and minimax versions of the models are investigated both in the plane and on the network.