GNSS, Map Matching, and Dead Reckoning
GNSS, map matching, and dead reckoning are complementary methods an in-car navigation system uses to estimate where the vehicle is. GNSS supplies satellite-based position and time, map matching relates the estimate to a plausible road, and dead reckoning continues the estimate from vehicle motion when satellite reception is weak.
GNSS
Global Navigation Satellite System is the generic term covering constellations such as GPS, Galileo, GLONASS, and BeiDou. A receiver combines signals from visible satellites to estimate position. Buildings, tunnels, terrain, interference, and antenna placement can reduce accuracy or availability.
Map matching
Raw coordinates rarely lie perfectly on a digital road centerline. Map-matching software considers position uncertainty, heading, speed, road geometry, route context, and legal connections to select the most plausible road segment. It can still choose the wrong parallel road, ramp, or level in a complex junction.
Dead reckoning
Dead reckoning starts from a known position and propagates it using wheel speed, steering, inertial sensors, or other motion data. It helps through tunnels and garages, but small sensor errors accumulate over time, so GNSS or another landmark must correct the estimate. ESA's Navipedia describes in-vehicle dead reckoning with gyroscopes and vehicle sensors for GNSS outages. ESA Navipedia: Road Navigation
Why the combination matters
The three methods support stable turn guidance, correct road selection, estimated arrival time, charging-route planning, and location-based vehicle functions. None guarantees lane-level truth in every environment, and the displayed map position should not be treated as a safety-critical perception system.
Learn more
See Vehicle positioning for vehicle positioning sensors and fusion, and Navigation systems for maps, routing, traffic, and EV charging guidance.