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World Geodetic System

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Geodesy
Fundamentals
Concepts
Technologies
Standards (history)
NGVD 29 Sea Level Datum 1929
OSGB36 Ordnance Survey Great Britain 1936
SK-42 Systema Koordinat 1942 goda
ED50 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 Internet link to a point 2010

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). The standard is published and maintained by the United States National Geospatial-Intelligence Agency.[1]

Definition

WGS 84 reference frame. The oblateness of the ellipsoid is exaggerated in this image.

The coordinate origin of WGS 84 is meant to be located at the Earth's center of mass; the uncertainty is believed to be less than 2 cm.[2]

Handheld GPS receiver indicating the Greenwich meridian is 0.089 arcminutes (or 5.34 arcseconds) west to the WGS 84 datum (the IERS Reference Meridian)

The WGS 84 meridian of zero longitude is the IERS Reference Meridian,[3] 5.3 arc seconds or 102 metres (335 ft) east of the Greenwich meridian at the latitude of the Royal Observatory.[4][5] (This is related to the fact that the local gravity field at Greenwich doesn't point exactly through the Earth's center of mass, but rather "misses west" of the center of mass by about that 102 meters.) The longitude positions on WGS 84 agree with those on the older North American Datum 1927 at roughly 85° longitude west, in the east-central United States.

The WGS 84 datum surface is an oblate spheroid with equatorial radius a = 6378137 m at the equator and flattening f = 1/298.257223563. The refined value of the WGS 84 gravitational constant (mass of Earth's atmosphere included) is GM = 3986004.418×108 m3/s2. The angular velocity of the Earth is defined to be ω = 72.92115×10−6 rad/s.[6]

This leads to several computed parameters such as the polar semi-minor axis b which equals a × (1 − f) = 6356752.3142 m, and the first eccentricity squared, e2 = 6.69437999014×10−3.[6]

Updates and new standards

The original standardization document for WGS 84 was Technical Report 8350.2, published in September 1987 by the Defense Mapping Agency (which later became the National Imagery and Mapping Agency). New editions were published in September 1991 and July 1997; the latter edition was amended twice, in January 2000 and June 2004.[7] The standardization document was revised again and published in July 2014 by the National Geospatial-Intelligence Agency as NGA.STND.0036.[8] These updates provide refined descriptions of the Earth and realizations of the system for higher precision.

WGS 84 has most recently been updated to use the reference frame G2139, which was released on January 3, 2021 as an update to G1762' (with a prime).[9] This frame is aligned with the IGb14 realization of the International Terrestrial Reference Frame (ITRF) 2014 and uses new Antex standard.[10][9]

Updates to the original geoid for WGS 84 are now published as a separate Earth Gravitational Model (EGM), with improved resolution and accuracy. Likewise, the World Magnetic Model (WMM) is updated separately. The current version of WGS 84 uses EGM2008 and WMM2020.[11][12]

Solution for Earth orientation parameters consistent with ITRF2014 is also needed (IERS EOP 14C04).[13]

Identifiers

Components of WGS 84 are identified by codes in the EPSG Geodetic Parameter Dataset:[14]

See also

References

  1. ^ "World Geodetic System 1984 (WGS 84)". Office of Geomatics, National Geospatial-Intelligence Agency. Retrieved 2022-12-21.
  2. ^ "The EGM96 Geoid Undulation with Respect to the WGS84 Ellipsoid". NASA.
  3. ^ European Organisation for the Safety of Air Navigation and IfEN: WGS 84 Implementation Manual, p. 13. 1998
  4. ^ "Greenwich Meridan, Tracing its History". Gpsinformation.net. Retrieved 2017-05-24.
  5. ^ Malys, Stephen; Seago, John H.; Palvis, Nikolaos K.; Seidelmann, P. Kenneth; Kaplan, George H. (1 August 2015). "Why the Greenwich meridian moved". Journal of Geodesy. 89 (12): 1263–1272. Bibcode:2015JGeod..89.1263M. doi:10.1007/s00190-015-0844-y.
  6. ^ a b "Department of Defense World Geodetic System 1984" (PDF) (2nd ed.). Defense Mapping Agency. 1991-09-01. Archived (PDF) from the original on August 3, 2021.
  7. ^ "DMA TR 8350.2 WGS". IHS Markit Standards Store. Retrieved 2022-12-26.
  8. ^ "Data collection of WGS 84 information — or is it?". GPS World. 2 November 2016.
  9. ^ a b "(U) Recent Update to WGS 84 Reference Frame and NGA Transition to IGS ANTEX" (PDF). Retrieved 2023-01-15.{{cite web}}: CS1 maint: url-status (link)
  10. ^ Australian Government - Geoscience Australia (2017-03-20). "What are the limitations of using World Geodetic System 1984 in Australia?". www.ga.gov.au. Retrieved 2022-05-16.
  11. ^ "NGA Geomatics - WGS 84". earth-info.nga.mil. Retrieved 2019-03-19.
  12. ^ "World Magnetic Model". NCEI. Retrieved 2020-01-23.
  13. ^ "Evolution of the World Geodetic System 1984 (WGS 84) Terrestrial Reference Frame" (PDF). Retrieved 2023-01-15.
  14. ^ "World Geodetic System 1984 ensemble". EPSG Geodetic Parameter Dataset. Retrieved 2022-12-21.
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