An agricultural vehicle comprises a left frame and a right frame. A left wheel is rotatable with respect to the left frame and a right wheel is rotatable with respect to the right frame. A first leg extends upward from the left frame and a second leg extends upward from the right frame to connect the legs to the beam. A data processor estimates a reference point on or below the vehicle and an angular orientation or attitude of the beam relative to the reference point based on positions of location-determining receivers associated with the beam. An upper carriage is laterally movable along the beam. A lower carriage is suspended from the upper carriage by a plurality of vertical supports, such that a target lateral position of the upper carriage establishes an actual lateral position of the lower carriage.
