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Coordinate conversion is composed of a number of different types of conversion: format change of geographic coordinates, conversion of coordinate systems, or transformation to different geodetic datums. Geographic coordinate conversion has applications in cartography, surveying, navigation and geographic information systems.
The definition of NAD 83(1986) is based on the GRS 80 spheroid, as was WGS 84, so many older publications indicate no difference. WGS 84 subsequently changed to a slightly less flattened spheroid. This change in flattening is about 0.1 mm, a difference so small that computational programs often do not distinguish between the two ellipsoids. [13]
The ECEF that is used for the Global Positioning System (GPS) is the geocentric WGS 84, which currently includes its own ellipsoid definition. [5] Other local datums such as NAD 83 may also be used. Due to differences between datums, the ECEF coordinates for a location will be different for different datums, although the differences between ...
Using it, it becomes possible to convert regional surveying points into the WGS84 locations used by GPS. For example, starting with the Gauss–Krüger coordinate, x and y, plus the height, h, are converted into 3D values in steps: Undo the map projection: calculation of the ellipsoidal latitude, longitude and height (W, L, H)
The NAD83 map datum is sufficiently close to WGS84 for initial use. It is best to double check on a mapping site such as WikiMapia. Cordinates obtained in China from commercial sources (Google, Bing, Baidu, etc.) may be obfuscated with GCJ-02 or BD-09. Vector sources are more frequently affected than satellite sources.
The WGS 84 datum surface is an oblate spheroid with equatorial radius a = 6 378 137 m at the equator and flattening f = 1 ⁄ 298.257 223 563. The refined value of the WGS 84 gravitational constant (mass of Earth's atmosphere included) is GM = 3.986 004 418 × 10 14 m 3 /s 2. The angular velocity of the Earth is defined to be ω = 72.921 15 × ...
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]
To improve the National Spatial Reference System (NSRS), the National Geodetic Service will replace the North American Datum of 1983 (NAD 83) and the North American Vertical Datum of 1988 (NAVD 88) with a new geometric reference frame and geopotential datum in 2025. [3] [6]