A system for printing an image on a surface includes a robot, a printhead having a reference line printing mechanism, and a reference line sensor. The robot has at least one arm. The printhead is mounted to the arm and is movable by the arm over a surface along a rastering path while printing a new image slice on the surface. The reference line printing mechanism is configured to print a reference line on the surface when printing the new image slice. The reference line sensor is configured to sense the reference line of an existing image slice and transmit a signal to the robot causing the arm to adjust the printhead in a manner such that a side edge of the new image slice is aligned with the side edge of the existing image slice.