Controlling the position of an agricultural implement coupled to an agricultural vehicle based upon three-dimensional topography data

A system for controlling the position of an agricultural implement coupled to an agricultural vehicle comprises a control unit connected to a field topography database containing three-dimensional data of the topography of a field, a location signal generation arrangement providing location data of the position of the vehicle and/or the implement in the field, an implement position sensor arranged to sense the position of the implement with respect to the ground and to a positioning arrangement configured to move the implement in response to position control signals from the control unit. The control unit is operable to provide the control signals based upon a combination of actual position data received from the implement position sensor and expected required position change data that are derived from elevation data recalled from the field topography database based upon the location data.