https://www.gpsrchive.com/Shared/Satellites/GPS%20vs%20GLONASS%20vs%20Galileo.html GPS vs GLONASS vs Galileo System Overview Constellation Geometry Earth Geometry GPS Geometry GLONASS Geometry Galileo Geometry Geometry Comparison GPS vs GLONASS GPS vs Galileo Galileo vs GLONASS Position Calculation Satellite Selection Satellite Visibility System Overview * GPS + Operated by the United States Air Force. + Global coverage available since April 1995. + Space segment includes 32 satellites arranged into 6 orbital planes, each with a minimum of 4 satellites. + Satellties Orbit the Earth at an inclination of 55deg and an altitude of 12,550 miles (20,200 km). + Each satellite circles the Earth once every 11 hours and 58 minutes. + Transmits signals for civillian use over L1 (1575.42 MHz) and L5 (1176.45 MHz) bands. + Provides a positional accuracy of 11.4 - 25.5 feet (3.5 - 7.8 meters). * GLONASS + Operated by the Russian Aerospace Defence Forces. + Global coverage available since November 2011. + Space segment includes 24 satellites arranged into 3 orbital planes, each with 8 evenly spaced satellites. + Satellites orbit the Earth at an inclination of 64.8deg and an altitude of 11,868 miles (19,100 km). + Each satellites circles the Earth once every 11 hours and 15 minutes. + Transmits signals for civillian use over L1 (1602 MHz) band only. + Provides a positional accuracy of 16.4 - 32.8 feet (5 - 10 meters). * Galileo + Operated by the European GNSS Agency (GSA). + Global coverage available since 2019. + Space segment will include 30 satellites arranged into 3 orbital planes, each with 8 active and 2 spare satellites. + Satellites orbit the Earth at an inclination of 56deg and an altitude of 14,429 miles (23,222 km). + Each satellites circles the Earth once every 14 hours and 7 minutes. + Transmits signals for civillian use over E1 (1575.42 MHz) and E5a (1176.45 MHz) bands. + Provides a positional accuracy of 6.5 - 9.8 feet (2 - 3 meters). Constellation Geometry * Earth Geometry [Earth] [Earth] [Earth] [Earth] A view of the The Earths The Equator is The Inclination Earth rotational axis perpendicular angle for as seen from intersects its to the each GNSS above surface at the rotational axis constellation the continent North and South and is of Africa poles equidistant from measured from the poles the Equator * GPS Geometery [GPS] [GPS] [GPS] [GPS] Each orbital Constellation Satellites do Satellites circle plane geometry not pass the Earth is indexed cross section over the area in one of six with an displaying inside the orbital planes Inclination orbital plane remaining 35deg angle of 55deg intersections of latitude [World] [World] GPS satellite orbit paths GPS inclination angle orbit limits * GLONASS Geometery [GLO] [GLO] [GLO] [GLO] Each orbital Constellation Satellites do Satellites circle plane geometry not pass the Earth is indexed with cross section over the area in one of three an displaying inside the orbital planes Inclination orbital plane remaining 25.2deg angle of 64.8deg intersections of latitude [World] [World] GLONASS satellite orbit paths GLONASS inclination angle orbit limits * Galileo Geometry [GAL] [GAL] [GAL] [GAL] Each orbital Constellation Satellites do Satellites circle plane geometry not pass the Earth is indexed cross section over the area in one of three with an displaying inside the orbital planes Inclination orbital plane remaining 34deg angle of 56deg intersections of latitude [World] [World] Galileo satellite orbit paths Galileo inclination angle orbit limits Geometry Comparison * GPS vs GLONASS [GPS] [World] [World] GPS vs GLONASS Inclination angle orbit Satellite orbit limits paths * GPS vs Galileo [GPS] [World] [World] GPS vs Galileo Inclination angle orbit Satellite orbit limits paths * Galileo vs GLONASS [GAL] [World] [World] Galileo vs Inclination angle orbit Satellite orbit GLONASS limits paths Position Calculation * Consumer grade GPSr require a minimum of four satellite signals before they can calculate their position using trilateration. * One satellite is always reserved by the GPSr for the exclusive purpose of synchronizing all signals to a single atomic clock. * Knowing the distance to three satellites enables the GPSr to determine two potential solutions (and then guess the correct one). * An absolute location can be confidently calculated only when four (or more) distance values are available. * See this Garmin GPS Guide for beginners for additional information. [Position] [Position] [Position] The receiver is located Adding a third signal The true location is somewhere further isolates revealed only after a along the intersection of the solution to one of two fourth signal is applied to two signals. possibilites. the calculation. Satellite Selection * The GPSr will use the satellites in the best position for calculating your current location. [Satellite] * Zenith: Satellites located overhead (70deg - 90deg elevation) are best suited for vertical position calculations (GPS Elevation). * Inclination: Satellites visible midway in the sky (20deg - 70deg elevation) provide the best accuracy when calculating latitude and longitude. * Horizon: Satellites near the horizon (0deg - 20deg elevation) are more sensitive to geographic and atmospheric obstructions and consequently less relaible. Satellite Visiblity * Using a Satellite Visibility Prediction Service twe can determine which satellites will be visible for any given location, date and time. + Trimble GNSS Planning + STARFIRE (John Deere) * In the following example, we wanted to check GPS, GLONASS and Galileo satellite visibility from multiple latitudes in the northern hemisphere. * Results were plotted over a 24 hour period for N 5deg, N 25deg, N 45deg, N 65deg, and N 85deg latitude, all along E 25deg longitude. * While the number of visible satellites for each constellation fluctuated slightly, the sum of available satellites at each latitude did not vary significantly. * GPS seemed to provide the best satellite availability, while GLONASS and Galileo maintained slightly lower and similar visibility levels. * None of the charts indicated an insufficient number of total available satellites during the 24 hour test period. * Choosing GPS + GLONASS or GPS + Galileo appeared to always yield a similar number of available satellites. * The charts also revealed how the position of the satellites in the sky changes relative to the latitude from which they are observed. * Fewer satellites were available directly overhead as the latitude increased, and were instead positioned at more favorable elevation angles that contribute to improved horizontal accuracy at the expense of GPS derived elevation calculations. * Based on these observations, one can conclude that a dual-GNSS capable receiver would be a minimum requirement for relaible navigation at higher latitudes, where a Multi-GNSS and Multi-Band receiver is likely to offer the best performance. * Satellite visibility charts: + E 25deg N 5deg [GNSS] + E 25deg N 25deg [GNSS] + E 25deg N 45deg [GNSS] + E 25deg N 65deg [GNSS] + E 25deg N 85deg [GNSS] * *