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哈夫曼经典之作，学习gps很好的参考书； Global Positioning System (GPS), originally Navstar GPS,[1][2] is a space-based radionavigation system owned by the United States government and operated by the United States Air Force. It is a global navigation satellite system that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites.[3]