Reference ellipsoid

Reference Ellipsoid

A reference ellipsoid is a mathematically defined surface that approximates the geoid, which is the true physical shape of the Earth. It is an ellipsoid of revolution, meaning it is formed by rotating an ellipse about its minor axis. Reference ellipsoids are used in geodesy, cartography, and astronomy to provide a simple model of the Earth's shape for various calculations and measurements.

The coordinates on a reference ellipsoid are typically given in terms of latitude, longitude, and ellipsoidal height. These coordinates are essential for accurately mapping and navigating the Earth's surface.

Latitude

Latitude is the angle between a point on the Earth's surface and the equatorial plane. It is measured in degrees, with positive values indicating locations north of the equator and negative values indicating locations south of the equator.

Longitude

Longitude is the angle between a point on the Earth's surface and the prime meridian, which passes through Greenwich, England. It is also measured in degrees, with positive values indicating locations east of the prime meridian and negative values indicating locations west of the prime meridian.

Ellipsoidal Height

Ellipsoidal height (or geodetic height) is the distance from a point on the Earth's surface to the reference ellipsoid, measured along the normal to the ellipsoid. It is different from orthometric height, which is measured from the geoid.

Applications

Reference ellipsoids are used in various fields:

• In geodesy, they provide a basis for defining geodetic datums, which are coordinate systems used to map the Earth's surface.
• In cartography, they help in creating accurate maps and charts.
• In astronomy, they assist in calculating the positions of celestial objects relative to the Earth.

Common Reference Ellipsoids

Several reference ellipsoids have been defined for different purposes:

• The WGS 84 (World Geodetic System 1984) is widely used for GPS and other global applications.
• The GRS 80 (Geodetic Reference System 1980) is used for geodetic measurements and mapping.
• The Clarke 1866 ellipsoid was historically used in North America.

See Also

• Geoid
• Geodetic datum
• Map projection
• Geodesy
• Cartography
• Astronomy

Related Pages

• Latitude
• Longitude
• Ellipsoidal height
• WGS 84
• GRS 80
• Clarke 1866