A harvester, comprising: a header configured to gather harvested material into the harvester; a conveyance subsystem configured to convey the harvested material from the harvester to a receiving vehicle during a harvesting operation; a controllable subsystem; a vehicle position detection system configured to detect a characteristic of a position of the harvester relative to a position of the receiving vehicle and to determine whether the receiving vehicle is out of range of the material conveyance subsystem so the material conveyance subsystem is not conveying the harvested material to the receiving vessel of the receiving vehicle; wherein the vehicle position detection system configured to determine whether the receiving vehicle is in a compromised position relative to the harvester, in which conveyance of the harvested material to the receiving vessel is compromised, based on the characteristic of the position of the harvester relative to the position of the receiving vehicle and, if the characteristic of the position of the harvester relative to the position of the receiving vehicle indicates that the receiving vehicle is out of range of the material conveyance subsystem, then to determine that the receiving vehicle is in the compromised position; a control system configured to generate a control signal to control the controllable subsystem of the harvester if the vehicle position detection system detects that the receiving vehicle is in the compromised position; characterized in that the vehicle position detection system is configured to determine whether the receiving vehicle is likely to be out of range of the material conveyance subsystem within a time threshold; and if so, to determine that the receiving vehicle is in the compromised position. a header configured to gather harvested material into the harvester; a conveyance subsystem configured to convey the harvested material from the harvester to a receiving vehicle during a harvesting operation; a controllable subsystem; a vehicle position detection system configured to detect a characteristic of a position of the harvester relative to a position of the receiving vehicle and to determine whether the receiving vehicle is out of range of the material conveyance subsystem so the material conveyance subsystem is not conveying the harvested material to the receiving vessel of the receiving vehicle; wherein the vehicle position detection system configured to determine whether the receiving vehicle is in a compromised position relative to the harvester, in which conveyance of the harvested material to the receiving vessel is compromised, based on the characteristic of the position of the harvester relative to the position of the receiving vehicle and, if the characteristic of the position of the harvester relative to the position of the receiving vehicle indicates that the receiving vehicle is out of range of the material conveyance subsystem, then to determine that the receiving vehicle is in the compromised position; a control system configured to generate a control signal to control the controllable subsystem of the harvester if the vehicle position detection system detects that the receiving vehicle is in the compromised position; characterized in that the vehicle position detection system is configured to determine whether the receiving vehicle is likely to be out of range of the material conveyance subsystem within a time threshold; and if so, to determine that the receiving vehicle is in the compromised position.