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Earth's circumference is the distance around Earth. Measured around the equator, it is 40,075.017 km (24,901.461 mi). Measured passing through the poles, the circumference is 40,007.863 km (24,859.734 mi). Measurement of Earth's circumference has been important to navigation since ancient times.
In geodesy, the figure of the Earth is the size and shape used to model planet Earth. The kind of figure depends on application, including the precision needed for the model. A spherical Earth is a well-known historical approximation that is satisfactory for geography , astronomy and many other purposes.
The World Geodetic System ( WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also describes the associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM).
An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximations. It is a spheroid (an ellipsoid of revolution) whose minor axis (shorter diameter), which connects the ...
Earth radius (denoted as RšØ or ) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly 6,378 km (3,963 mi) ( equatorial radius, denoted a) to a minimum of nearly 6,357 km (3,950 mi) ( polar radius, denoted b ).
The centimetre ( SI symbol: cm) is a unit of length in the metric system equal to 10ā2 metres ( 1 100 m = 0.01 m ). To help compare different orders of magnitude, this section lists lengths between 10 ā2 m and 10 ā1 m (1 cm and 1 dm). 1 cm ā 10 millimetres. 1 cm ā 0.39 inches. 1 cm ā edge of a square of area 1 cm 2.
Geodetic coordinates. Geodetic coordinates are a type of curvilinear orthogonal coordinate system used in geodesy based on a reference ellipsoid . They include geodetic latitude (north/south) Ļ, longitude (east/west) Ī», and ellipsoidal height h (also known as geodetic height [1] ). The triad is also known as Earth ellipsoidal coordinates [2 ...
The reverse conversion is harder: given X-Y-Z can immediately get longitude, but no closed formula for latitude and height exists. See "Geodetic system." Using Bowring's formula in 1976 Survey Review the first iteration gives latitude correct within 10-11 degree as long as the point is within 10,000 meters above or 5,000 meters below the ellipsoid.