Vehicle guidance-maintaining horizontal laser

A laser guidance sub-assembly for a land vehicle having an upright axis comprising;

• a diode device for emitting a vertical line of laser light,
• a beam director for directing the vertical line of light in a horizontal beam and rotating the horizontal beam about a beam director axis to move the horizontal beam between circumferentially spaced locating stations,
• said assembly characterized by an alignment mechanism for maintaining the vertical line of light in parallel alignment with gravity to compensate for misalignment of said upright axis of the vehicle from vertical to maintain the vertical line of laser light aligned with gravity as said vehicle moves over an uneven plot.

A method of guiding a carriage having an upright axis over a plot comprising the steps of;

• emitting a vertical line of laser light defining a beam extending in the generally horizontal direction and generally radially from an upright axis,
• rotating the horizontal beam about the upright axis to move the horizontal beam between circumferentially spaced locating stations, and reflecting the horizontal beam in a reflected beam back from locating stations, detecting the reflected beam from the locating stations, locating the carriage from the reflected beam, and guiding the carriage over the plot in response to continuous locating of the carriage,
• said method characterized by moving the vertical line of light relative to the upright axis to compensate for misalignment of the upright axis from vertical in response to movement of the carriage over non-horizontal terrain.