GPS (Global Positioning System) is an outdoor localization system that measures time of flight of a radio signal from a number of satellites in earth orbit.

GPS (Global Positioning System) is an outdoor localization system that measures time of flight of a radio signal from a number of satellites in earth orbit. Each satellite sends a very precisely time-stamped signal that also includes its current location in earth orbit. By comparing the time difference in when signals from multiple satellites arrive with the time stamp and location, the position of the receiver can be worked out using triangulation. As GPS necessitates a line of sight to the satellites (although it works through clouds and rain), it is not suitable for indoor localization. It is usually accurate to about 10-15m. Using Differential GPS, which also takes into account signals from earth-based ground stations, accuracy can be improved to about 10cm.

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