Abstract: An automatic ground marking apparatus including a carriage (1) responsive to carriage control signals for traversing the ground (5), the carriage having a controllable steering and drive system, a controllable marking system and a position determining system (6) arranged to determine the position of the carriage. The ground marking apparatus further includes a processor (8) responsive to the position determining system and operatively executing a software product for generating the carriage control signals to cause the carriage (1) to mark out a predetermined sign (14) on the ground. The position determining system (6) suitably employs a laser beam (4) and reflective tracking prism (2), and the predetermined sign may be defined by data points stored in a file (9) accessed by the processor (8) (FIG. 1).