Editing World Geodetic System (section)

==Definition==
[[File:WGS_84_reference_frame_(vector_graphic).svg|thumb|upright=1.25|left|WGS&nbsp;84 reference frame. The oblateness of the ellipsoid is exaggerated in this image.]]
The coordinate origin of WGS&nbsp;84 is meant to be located at the Earth's [[center of mass]]; the uncertainty is believed to be less than {{val|2|u=cm}}.<ref>{{cite web| url = http://cddis.nasa.gov/926/egm96/doc/S11.HTML | publisher = [[NASA]] | title = The EGM96 Geoid Undulation with Respect to the WGS84 Ellipsoid}}</ref>

[[File:Garmin GPS at Greenwich Observatory.jpg|thumb|upright=1.2|Handheld GPS receiver at the [[Royal Observatory, Greenwich]], indicating that the [[Prime meridian (Greenwich)|Greenwich meridian]] is 0.089 [[arcminute]]s (or 5.34 [[arcsecond]]s) west of the WGS&nbsp;84 datum (the [[IERS Reference Meridian]])]]
The WGS&nbsp;84 meridian of zero longitude is the [[IERS Reference Meridian]],<ref name="Manual">[[EUROCONTROL|European Organisation for the Safety of Air Navigation]] and [[Institute of Geodesy and Navigation|IfEN]]: WGS&nbsp;84 Implementation Manual, p. 13. 1998</ref> 5.3 [[Minute of arc|arc seconds]] or {{convert|102|m|ft|}} east of the [[Greenwich meridian]] at the latitude of the [[Royal Observatory, Greenwich|Royal Observatory]].<ref>{{cite web|url=http://gpsinformation.net/main/greenwich.htm |title=Greenwich Meridan, Tracing its History |website=Gpsinformation.net |access-date=24 May 2017}}</ref><ref name="Malys et al. 2015">{{cite journal | title = Why the Greenwich meridian moved | first1 = Stephen | last1 = Malys | first2 = John H. | last2 = Seago | first3 = Nikolaos K. | last3 = Palvis | first4 = P. Kenneth | last4 = Seidelmann | first5 = George H. | last5 = Kaplan | journal = Journal of Geodesy | date = 1 August 2015 | volume = 89 | issue = 12 | pages = 1263–1272 | doi = 10.1007/s00190-015-0844-y| bibcode = 2015JGeod..89.1263M | doi-access = free }}</ref> (This is related to the fact that the local gravity field at Greenwich [[Vertical deflection|does not point exactly]] through the Earth's center of mass, but rather "misses west" of the center of mass by about 102 meters.) The longitude positions on WGS&nbsp;84 agree with those on the older [[North American Datum|North American Datum 1927]] at roughly [[85th meridian west|85° longitude west]], in the east-central United States.

The WGS&nbsp;84 datum surface is an [[oblate spheroid]] with equatorial radius {{mvar|a}} = {{val|6378137|u=m}} at the [[equator]] and [[flattening]] {{mvar|f}} = {{frac|1|{{val|298.257223563}}}}. The refined value of the WGS&nbsp;84 [[Standard gravitational parameter|gravitational constant]] (mass of Earth's atmosphere included) is {{mvar|GM}} = {{val|3.986004418e14|u=m3|up=s2}}. The angular velocity of the Earth is defined to be {{mvar|ω}} = {{val|72.92115e-6|u=rad|up=s}}.<ref name="Second Edition">{{cite web| url = https://apps.dtic.mil/sti/pdfs/ADA280358.pdf | archive-url = https://web.archive.org/web/20210803171602/https://apps.dtic.mil/sti/pdfs/ADA280358.pdf | url-status = live | archive-date = 3 August 2021 | title = Department of Defense World Geodetic System 1984 | edition = 2nd | date = 1 September 1991 | publisher = Defense Mapping Agency}}</ref>

This leads to several computed parameters such as the polar semi-minor axis {{mvar|b}} which equals {{math|''a'' × (1 − ''f'')}} = {{val|6356752.3142|u=m}}, and the first eccentricity squared, {{math|''e''<sup>2</sup>}} = {{val|6.69437999014e-3}}.<ref name="Second Edition"/>