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Grid-based transformations directly convert map coordinates from one (map-projection, geodetic datum) pair to map coordinates of another (map-projection, geodetic datum) pair. An example is the NADCON method for transforming from the North American Datum (NAD) 1927 to the NAD 1983 datum. [ 26 ]
Geodetic latitude and geocentric latitude have different definitions. Geodetic latitude is defined as the angle between the equatorial plane and the surface normal at a point on the ellipsoid, whereas geocentric latitude is defined as the angle between the equatorial plane and a radial line connecting the centre of the ellipsoid to a point on the surface (see figure).
A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame, or terrestrial reference frame) is a global datum reference or reference frame for unambiguously representing the position of locations on Earth by means of either geodetic coordinates (and related vertical coordinates) or geocentric coordinates. [1]
The local ENU coordinates are formed from a plane tangent to the Earth's surface fixed to a specific location and hence it is sometimes known as a "Local Tangent" or "local geodetic" plane. By convention the east axis is labeled x {\displaystyle x} , the north y {\displaystyle y} and the up z {\displaystyle z} .
The Earth-centered, Earth-fixed coordinate system (acronym ECEF), also known as the geocentric coordinate system, is a cartesian spatial reference system that represents locations in the vicinity of the Earth (including its surface, interior, atmosphere, and surrounding outer space) as X, Y, and Z measurements from its center of mass.
WKT can describe coordinate reference systems. For example, the WKT below describes a two-dimensional geographic coordinate reference system with a latitude axis first, then a longitude axis. The coordinate system is related to Earth by the WGS84 geodetic datum:
BeiDou Coordinate System, China Terrestrial Reference Frame (CTRF) 2000 = ITRF97 at epoch 2000.0; own implementation. GLONASS PZ-90.11 is nominally its own system, but is quite close to ITRF and uses many of the same techniques. [2] National systems: United States: WGS 84 (see above); domestic use is mainly based on NAD 83 instead.
Each projected coordinate system, such as "Universal Transverse Mercator WGS 84 Zone 26N," is defined by a choice of map projection (with specific parameters), a choice of geodetic datum to bind the coordinate system to real locations on the earth, an origin point, and a choice of unit of measure. [2]