This point is known as the origin point of the datum. A point on the surface of the spheroid is matched to a specific position on the surface of the earth. WGS84 is used for GPS, while WGS 84/Pseudo-Mercator is a variant and used by web mapping tools such as Open Street Map.Ī local datum aligns its spheroid to fit the earth’s surface in a particular area closely. The most recently developed and widely used datum is the World Geodetic System 1984 (WGS84). An earth-centred, or geocentric, datum uses the earth’s centre of mass as the origin ( reference). In the last 15 years, satellite data has provided geodesists with new measurements to define the best earth-fitting spheroid, which relates coordinates to the earth’s centre of mass. While a spheroid approximates the shape of the earth, a datum defines the position of the spheroid relative to the centre of the earth. Sydney, for example, has a latitude of 33.877° S and a longitude of 151.215° E. In a geographic coordinate system, a point is referenced by its latitude and longitude values ( reference). It includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid). A Geographic Coordinate System (GCS) uses a three-dimensional spherical surface to define locations on the earth.
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