Beidou system Global Navigation Satellite System Fundamentals Organizations related to GNSS United Nations International Committee on Global Navigation Satellite Systems (ICG) Institute of Navigation (ION) GNSS Meetings The International GNSS Service (IGS) International Global Navigation Satellite Systems Society Inc (IGNSS) International Earth Rotation and Reference Systems Service (IERS) International GNSS Service (IGS) US National Executive Committee for Space-Based Positioning, Navigation, and Timing US National Geodetic Survey Orbits for the Global Positioning System satellites in the Global Navigation Satellite System UNAVCO GNSS Modernization Asia-Pacific Economic Cooperation (APEC) GNSS Implementation Team Supportive or illustrative sites GPS and GLONASS Simulation (Java applet) Simulation and graphical depiction of the motion of space vehicles, including DOP computation. GPS, GNSS, Geodesy and Navigation Concepts in depth American inventions Aircraft instruments Avionics Geodesy Maritime communication Navigation