A GPS-based control system for positioning a nozzle projection onto a predetermined roadway mark path includes a vehicle having an attached paint carriage which is laterally movable with respect to the vehicle, a first GPS antenna, a first GPS receiver responsive to the first GPS antenna, a first signal processor for determining the geographical location of the first GPS antenna, a linear motion and position sensor, a GPS location processor for determining the absolute GPS location of the paint carriage, a coordinate transform processor for transforming the absolute GPS location of the paint carriage into a location in a coordinate system other than GPS, a comparator for comparing the location of the paint carriage in the other coordinate system to a desired roadway mark path according to the other coordinate system, and a control system for positioning the nozzle projection onto the roadway mark path.