Living Reference Work Entry

Encyclopedia of Geodesy

pp 1-4

Date: Latest Version

GPS, Reference Systems

  • Geoffrey BlewittAffiliated withNevada Bureau of Mines and Geology/Seismological Laboratory, University of Nevada Email author 


GPS. Global Positioning System, the US-operated Global Navigation Satellite System (GNSS) that can be used to determine a user’s position, in terms of latitude, longitude, and height coordinates, anywhere on the globe with a clear view of the sky.

Reference system. A conventionally adopted system that specifies precisely the meaning of a user’s position.

Essential Concepts

GPS consists of three segments: (1) the space segment of typically 30 satellites that transmit microwave ranging signals and signals containing information on satellite positions and satellite atomic clock time; (2) the control segment of globally distributed stations that monitor, control, and upload data to the space segment; and (3) the user segment consisting of anybody with a GPS receiver who uses the space segment to find their position (Hofmann-Wellenhof et al., 2008).

Geodetic coordinates, such as those obtained by GPS measurements, are generally defined with respect to some reference system that com ...

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