Line marking apparatus, system and method

A line marking apparatus, for use in a system that includes a source of a narrow beam of radiation which extends substantially horizontally along or parallel to a line to be marked, includes a wheeled chassis and a line marking head for dispensing line marking material. The marking head is supported on the chassis for lateral movement relative thereto, which movement is controlled by a controller that includes a detector which is movable with the marking head and is positioned and directed to detect such a beam of radiation, the marking head being movable together with the detector in response to a detected beam. Lateral movement of the marking head is thereby controlled such that the head and the detector substantially follow the line to be marked irrespective of whether the chassis deviates from the line direction.