GNSSposities

GNSSposities are the spatial coordinates of a point determined using Global Navigation Satellite Systems (GNSS). A GNSS receiver computes its position by processing signals from multiple satellites that broadcast precise timing and ephemeris data. Constellations such as GPS, GLONASS, Galileo, and BeiDou provide the necessary signals, and modern receivers commonly use pseudorange and carrier-phase measurements to estimate location and receiver clock error.

To determine position, at least four satellites are typically required. The measurements solve for three spatial coordinates and the receiver’s time offset in an Earth-centered, Earth-fixed (ECEF) frame. The resulting coordinates are usually expressed in a standard datum and can be converted to geographic latitude, longitude, and height. Height can be given as ellipsoidal height relative to the reference ellipsoid or as orthometric height above a geoid.

Time and reference frames are integral to GNSS positioning. Satellite clocks and the receiver’s time are referenced to a GNSS time scale (for example GPS Time) and must be related to civil time (UTC). Common geodetic reference frames include WGS84 and the International Terrestrial Reference Frame (ITRF), with positions typically transformed between these frames as needed.

Accuracy and error sources vary with conditions. Key factors include atmospheric delays (ionospheric and tropospheric), multipath, satellite clock and ephemeris errors, and receiver noise. Augmentation and correction methods improve reliability and accuracy: SBAS, differential GPS (DGPS), real-time kinematic (RTK), and Precise Point Positioning (PPP) can provide centimeter to decimeter level accuracy under favorable conditions.

GNSSposities support a wide range of applications, including navigation, surveying, mapping, geodesy, agriculture, and autonomous systems, where precise, time-synchronized location data is essential.