1. A method for identifying an edge of a crop, the method comprising: emitting a transmitted radiation pattern of structured light within a defined spatial zone toward a top and a bottom of the crop from a mobile vehicle, the transmitted radiation pattern comprising multiple generally linear beams spaced apart from one another, collecting one or more images of the defined spatial zone; detecting a presence of crop edge between a harvested portion and unharvested portion of a field based on an observed illumination radiation pattern on the crop edge formed by at least a portion of the transmitted radiation pattern, the observed illumination radiation pattern associated with an upper interface and a lower interface; the upper interface defining a boundary between a top of the unharvested crop and the spatial area thereabove, the lower interface defining a boundary between a bottom of the unharvested crop and the ground or between the harvested crop and the ground; and identifying image coordinate data, in the collected image, associated with the detected crop edge for guidance of the vehicle, where in a structured light mode the image coordinate data generally locates the crop edge in at least two dimensions and where in a range finding mode the image coordinate data limits the defined spatial zone for subsequent selective gathering of refined three dimensional data for the crop edge.