WGS84

World Geodetic System 1984 (WGS84) is a global geodetic reference frame and ellipsoidal model of the Earth used for positioning, navigation, and mapping. It provides a standard coordinate system for expressing locations on and above the Earth's surface and serves as the de facto reference for GPS positioning, satellite navigation, and many geographic information systems.

The WGS84 reference ellipsoid is defined by a semi-major axis of 6,378,137.0 meters and a reciprocal flattening of 298.257223563, yielding an eccentricity squared of about 0.00669437999014. The frame is Earth-centered and Earth-fixed (ECEF), with the origin at the Earth's center of mass. Its axes are fixed to the Earth: the X-axis intersects the equator at 0° longitude, the Z-axis is aligned with the mean rotation axis (near the North Pole), and the Y-axis completes a right-handed system. The orientation is tied to international reference frames through the IERS and is realized continuously to align with the International Terrestrial Reference System (ITRS) over time.

WGS84 positions can be expressed in latitude, longitude, and height above the ellipsoid (Lh) or in Cartesian X, Y, Z coordinates in the ECEF frame. The epoch associated with WGS84 is 1984.0, and the frame is maintained and updated to reflect refinements in the global reference system, while keeping backward compatibility for GPS and other global positioning applications.

Applications of WGS84 include global navigation, surveying, mapping, and geospatial analysis. It remains the standard global reference frame for many systems and is widely used in combination with local datums through conversion tools and transformation parameters.

See also: Geodetic datum, ECEF, ITRS, GPS.