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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]
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).
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).
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]
GNSS systems: [2] Galileo Terrestrial Reference Frame (GTRF), ITRF2005; own implementation using IGS sites.; GPS just uses WGS 84, ITRF2020 since January 2024 (but used many versions of WGS 84 before), a little modified with International GNSS Service (IGS) implementation, IGS20.
Below is an example of a datum shift operation in WKT 2 format. Contrarily to an equivalent description in WKT 1 format, the WKT 2 description specifies the source and target coordinate reference systems, together with the domain of validity and the accuracy (in metres) that we can expect from this operation:
European Datum 1950: SAD69: South American Datum 1969: GRS 80: Geodetic Reference System 1980: ISO 6709: Geographic point coord. 1983: NAD 83: North American Datum 1983: WGS 84: World Geodetic System 1984: NAVD 88: N. American Vertical Datum 1988: ETRS89: European Terrestrial Ref. Sys. 1989: GCJ-02: Chinese obfuscated datum 2002: Geo URI ...
Geodetic coordinates ,, in the new datum are modeled as polynomials of up to the ninth degree in the geodetic coordinates ,, of the original datum . For instance, the change in ϕ B {\displaystyle \phi _{B}} could be parameterized as (with only up to quadratic terms shown) [ 30 ] : 9