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The original WGS84 model had an absolute accuracy of 1–2 meters. WGS84 (G730) first incorporated GPS observations, taking the accuracy down to 10 cm/component rms. [14] All following revisions including WGS84 (G873) and WGS84 (G1150) also used GPS. [15] WGS 84 (G1762) is the sixth update to the WGS reference frame. [14]
An ellipsoidal model describes only the ellipsoid's geometry and a normal gravity field formula to go with it. Commonly an ellipsoidal model is part of a more encompassing geodetic datum. For example, the older ED-50 (European Datum 1950) is based on the Hayford or International Ellipsoid. WGS-84 is peculiar in that the same name is used for ...
The first EGM, EGM84, was defined as a part of WGS84 along with its reference ellipsoid.WGS84 combines the old GRS 80 with the then-latest data, namely available Doppler, satellite laser ranging, and Very Long Baseline Interferometry observations, and a new least squares method called collocation. [3]
Up to the 1960s, formulas based on the Hayford ellipsoid (1924) and of the famous German geodesist Helmert (1906) were often used. [citation needed] The difference between the semi-major axis (equatorial radius) of the Hayford ellipsoid and that of the modern WGS84 ellipsoid is 251 m; for Helmert's ellipsoid it is only 63 m.
For example, in the WGS 84 spheroid used by today's GPS systems, the reciprocal of the flattening / is set to be exactly 298.257 223 563. The difference between a sphere and a reference ellipsoid for Earth is small, only about one part in 300. Historically, flattening was computed from grade measurements.
[1] [2] [3] The GRS80 gravity model has been followed by the newer more accurate Earth Gravitational Models, but the GRS80 reference ellipsoid is still the most accurate in use for coordinate reference systems, e.g. for the international ITRS, the European ETRS89 and (with a 0,1 mm rounding error) for WGS 84 used for the American Global ...
As noted above, the iterative solution to the inverse problem fails to converge or converges slowly for nearly antipodal points. An example of slow convergence is (Φ 1, L 1) = (0°, 0°) and (Φ 2, L 2) = (0.5°, 179.5°) for the WGS84 ellipsoid. This requires about 130 iterations to give a result accurate to 1 mm. Depending on how the inverse ...
An approximate definition of sea level is the datum WGS 84, an ellipsoid, whereas a more accurate definition is Earth Gravitational Model 2008 (EGM2008), using at least 2,159 spherical harmonics. Other datums are defined for other areas or at other times; ED50 was defined in 1950 over Europe and differs from WGS 84 by a few hundred meters ...