Agricultural harvester with closed loop ground tracking control

A method and apparatus for controlling an agricultural harvester having a cut crop receiving header coupled to a hydraulic cylinder. The header applies a force against the ground that is adjusted by applying pressure to the cylinder. Proportional raise and lower valves control the pressure in the cylinder. A pressure signal representing cylinder pressure is received. The difference between the measured pressure and the setpoint is used to compute input signals, which are transmitted to the valves. Cylinder pressure is maintained substantially at a setpoint, the setpoint being adjustable in response to varying terrain. The setpoint is set to a first value in falling terrain and a second value in rising terrain. At the top of a hill, the setpoint is reduced below the first value until ground contact is regained, and the pressure is recharged above the second value. Alternatively, header height may be measured and the valves controlled to maintain header position substantially constant relative to the ground or the harvester frame. Header lateral tilt is controlled while controlling either cylinder pressure or header height. A resume function returns the header from a raised position to a cutting position at the beginning of a new row.