Now, with DGPS, farmers can get those nice straight lines all the way across the field. Before the introduction of GPS and differential receivers in agriculture, farmers used a variety of methods to ensure they were driving the straight and narrow. Sometimes, for more conventional spraying using boom sprayers, farmers use bits of foam placed as markers, but that has problems, too, because sometimes the foam nozzle clogs. With DGPS systems on their equipment, farmers now use a row of lights on a dashboard display to aid in navigation. Using GPS and differential signals, the lightbar indicates if the farmer is off track.
Farmers can even spray at night when there's less wind.
Now you don't even need to see the field. You just follow the navigation lights.