Editing World Geodetic System (section)

==={{anchor|WGS84}}WGS&nbsp;84===
[[File:WGS84_mean_Earth_radius.svg|thumb|upright=1.15|Equatorial ({{mvar|a}}), polar ({{mvar|b}}) and mean Earth radii as defined in the 1984 World Geodetic System revision (not to scale)]]
In the early 1980s, the need for a new world geodetic system was generally recognized by the geodetic community as well as within the US Department of Defense. WGS 72 no longer provided sufficient data, information, geographic coverage, or product accuracy for all then-current and anticipated applications. The means for producing a new WGS were available in the form of improved data, increased data coverage, new data types and improved techniques. Observations from Doppler, satellite laser ranging and [[very-long-baseline interferometry]] (VLBI) constituted significant new information. An outstanding new source of data had become available from satellite radar altimetry. Also available was an advanced [[least squares]] method called [[Collocation method|collocation]] that allowed for a consistent combination solution from different types of measurements all relative to the Earth's gravity field, measurements such as the geoid, gravity anomalies, deflections, and dynamic Doppler.

The new world geodetic system was called WGS&nbsp;84. It is the reference system used by the [[Global Positioning System]]. It is geocentric and globally consistent within {{val|1|ul=m}}. Current geodetic realizations of the geocentric reference system family [[International Terrestrial Reference System]] (ITRS) maintained by the [[IERS]] are geocentric, and internally consistent, at the few-cm level, while still being metre-level consistent with WGS&nbsp;84.

The WGS&nbsp;84 [[reference ellipsoid]] was based on [[GRS 80]], but it contains a very slight variation in the inverse flattening, as it was derived independently and the result was rounded to a different number of significant digits.<ref>{{Cite book | last = Hooijberg | first = Maarten | date = 18 December 2007 | title = Geometrical Geodesy: Using Information and Computer Technology | location = Germany | publisher = Springer Berlin Heidelberg | page = 20 | isbn = 9783540682257}}</ref> This resulted in a tiny difference of {{val|0.105|u=mm}} in the semi-minor axis.<ref>{{Cite web |title=USER DOCUMENTATION Programs: INVERSE, FORWARD, INVERS3D, FORWRD3D Versions 2.0 |url=https://geodesy.noaa.gov/PC_PROD/Inv_Fwd/readme.htm |access-date=23 May 2022 |website=geodesy.noaa.gov}}</ref>
The following table compares the primary ellipsoid parameters.

{| class="wikitable"
|-
! Ellipsoid reference
! [[Semi-major axis]] {{mvar|a}}
! [[Semi-minor axis]] {{mvar|b}}
! Inverse [[flattening]] {{frac|1|{{mvar|f}}}}
|-
! GRS 80
| {{val|6378137.0|u=m}}
| ≈ {{val|6356752.314140|u=m}}
| {{val|298.257222100882711}}...
|-
! WGS 84<ref>{{cite web | url = https://epsg.org/ellipsoid_7030/WGS-84.html | title = WGS&nbsp;84: Ellipsoid Details | website = EPSG Geodetic Parameter Dataset | access-date=21 December 2022}}</ref>
| {{val|6378137.0|u=m}}
| ≈ {{val|6356752.314245|u=m}}
| {{val|298.257223563}}
|}