The invention described herein uses the periodicity of the relative height of the surface of a crop or soil surface that is measured over a large area to control the position of a farm vehicle as it passes between rows of crops. The range and angle of return wave energy that are caused by a scanning...http://www.google.fr/patents/US5509486?utm_source=gb-gplus-shareBrevet US5509486 - Method of steering an agricultural vehicle
