World Geodetic System

GRAVIMETRIC DATUM ORIENTATION

DOPPLER SATELLITE GROUND STATIONS PROVIDING DATA FOR WGS 72 DEVELOPMENT

WORLDWIDE GEOMETRIC SATELLITE TRIANGULATION NETWORK, BC-4 CAMERAS

WGS84 mean Earth radius

WGS 84 reference frame (vector graphic)

Garmin GPS at Greenwich Observatory

World Geodetic System (WGS) is a standard for use in cartography, geodesy, and satellite navigation including GPS. The latest revision, WGS 84, established in 1984 and last updated in 2004, is currently in wide use worldwide. Its predecessor, WGS 72, was used for mapping and charting purposes before WGS 84 took over due to its improved accuracy and compatibility with satellite systems.

Overview

The World Geodetic System provides a consistent geographic coordinate system and a standard set of ellipsoid parameters to accurately describe the Earth's shape and size. WGS 84 is a geocentric system, meaning it is centered on the Earth's center of mass. It is defined by three primary components: an ellipsoid of revolution, a set of datum parameters, and a geoid that approximates mean sea level.

Ellipsoid

The WGS 84 ellipsoid is a mathematical representation of the Earth's shape, slightly flattened at the poles and bulging at the equator. This ellipsoid is defined by its semi-major axis (equatorial radius) and its flattening. The semi-major axis is approximately 6,378,137 meters, and the flattening is about 1/298.257223563.

Datum

The WGS 84 datum ties the ellipsoid to a specific location on the Earth's surface, serving as a reference point for geographic coordinate systems. This datum is crucial for ensuring that coordinates on a map correspond to actual locations on the Earth's surface.

Geoid

The WGS 84 geoid is an equipotential surface that approximates the mean sea level across the Earth's surface. It varies in height over the ellipsoid due to irregularities in the Earth's gravitational field. The geoid is used to measure precise surface elevations.

Applications

WGS 84 is the foundation for many global positioning systems, including the Global Positioning System (GPS). It ensures that GPS coordinates are consistent and accurate worldwide. WGS 84 is also used in aviation, maritime navigation, and for military applications, providing a common reference framework for mapping and spatial positioning.

History

The development of the World Geodetic System began in the 1960s, with the first version, WGS 60, being used by the United States Department of Defense. It was followed by WGS 66 and WGS 72, each improving on the previous version's accuracy and global applicability. WGS 84 was a significant update, incorporating satellite data to provide a more accurate representation of the Earth's shape and gravitational field.

Updates and Maintenance

The National Geospatial-Intelligence Agency (NGA) maintains WGS 84, with periodic updates to reflect changes in the Earth's shape due to tectonic movements, melting ice caps, and other factors. These updates ensure that WGS 84 remains a reliable global standard for geospatial data.

See Also

• Geographic coordinate system
• Global Positioning System (GPS)
• Geodesy
• Ellipsoid
• Geoid