Judging The Mud Below By The Sky Above

How does a bulldozer operator know exactly how deep to dig or how high to pile? One way is to calibrate where the blade is by using a laser beam shining at a known height. Ohio State University's Center for Mapping turned to the U.S. government's constellation of Global Positioning System (GPS) satellites for some heavenly precision. George C. Dedes, a center researcher, says a receiver mounted on a pole attached to the bulldozer's blade calculates where it is by comparing readings from several satellites. That determines the blade's position within a few centimeters.

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