哈夫曼經典之作，學習gps很好的參考書； 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]