World Geodetic System 84

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World Geodetic SystemFrom Wikipedia, the free encyclopedia

The World Geodetic Systemis a standard for use incartography, geodesy,andnavigation.Itcomprises a standard coordinate framefor the Earth, a standard spheroidalreference surface

(the datumor reference ellipsoid) for raw altitudedata, and a gravitationaleuipotential

surface(thegeoid) that defines the nominal sea level.

The latest revision is WGS 84(dating from !"#$ and last revised in %&&$), which was valid

up to a'out %&!&.!citation neededEarlier schemes included WGS 72, WGS 66, and WGS 60.

W*+ #$ is the reference coordinate system used 'y the*lo'al ositioning +ystem.

Contents

! -ain parameters % istory

/ The 0nited +tates 1epartment of 1efense World *eodetic +ystem !"22

$ The 0nited +tates 1epartment of 1efense World *eodetic +ystem !"3%

4 5 new World *eodetic +ystem6 W*+ #$

o 4.! 7ongitudes on W*+ #$

o 4.% 0pdates and new standards

2 +ee also

3 8eferences

# E9ternal links

Main parameters

The coordinate origin of W*+ #$ is meant to 'e located at the Earth:s center of mass; the

error is 'elieved to 'e less than % cm.%

The W*+ #$ meridian of or (transverse) radius a

? 2/3#!/3 m at the euatorand flatteningf? !@%"#.%43%%/42/.2The polar semiAminor

(conjugate) radius bthen euals atimes (! A f), or 2/4234%./!$% m.2

resently W*+ #$ uses the E*-"2(Earth *ravitational -odel !""2) geoid, revised in %&&$.

This geoid defines the nominal sea level surface 'y means of a spherical harmonicsseries ofdegree /2& (which provides a'out !&& km hori


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E*-"2 geoid from the W*+ #$ reference ellipsoid range from a'out B!&4 m to a'out

C#4 m.#E*-"2 differs from the original W*+ #$ geoid, referred to as E*-#$.

History

Efforts to supplement the various national surveyingsystems 'egan in the !"th century with

F.8. elmert:sfamous 'ooksMathematische und Physikalische Theorien der Physikalischen

Geodsie(Mathematical and Physical Theory of Physical Geodesy). 5ustriaand *ermany

founded theZentralbro fr die Internationale rdmessung(Dentral ureau of International

*eodesy), and a series of glo'al ellipsoidsof the Earth were derived (e.g., elmert !"&2,

ayford!"!&@ !"%$).

5 unified geodetic system for the whole world 'ecame essential in the !"4&s for several

reasons6

International space scienceand the 'eginning of astronautics. The lack of interAcontinental geodetic information.

The ina'ility of the large geodetic systems, such as European 1atum (E14&),orth

5merican 1atum(51), and Tokyo 1atum(T1), to provide a worldwide geoAdata

'asis

eed for glo'al maps for navigation,aviation, and geography.

Western Dold Warpreparedness necessitated a standardised,5T=Awide geospatial

reference system, in accordance with the 5T= +tandardisation 5greement

In the late !"4&s, the 0nited +tates 1epartment of 1efense, together with scientistsof other

institutions and countries, 'egan to develop the needed world system to which geodetic data

could 'e referred and compati'ility esta'lished 'etween the coordinates of widely separated

sites of interest. Efforts of the 0.+. 5rmy, avy and 5ir Force were com'ined leading to the

1o1 World *eodetic +ystem !"2& (W*+ 2&). The term datumas used here refers to a

smooth surface somewhat ar'itrarily defined as


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*ravimetric datum orientation

rior to W*+ 2&, the 0.+. 5rmy and0.+. 5ir Forcehad each developed a world system 'yusing different approaches to the gravimetric datum orientation method. To determine their

gravimetric orientation parameters, the 5ir Force used the mean of the differences 'etween

the gravimetric and astroAgeodetic deflectionsand geoid heights (undulations) at specifically

selected stations in the areas of the ma>or datums. The 5rmy performed an ad>ustment to

minimi


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after its implementation in !"23. The defining parameters of the W*+ 22 Ellipsoid were the

flattening (!@%"#.%4), determined from satellite data and the semima>or a9is (2,/3#,!$4

meters), determined from a com'ination of 1oppler satellite and astroAgeodetic data. 5

worldwide 4H 4H mean free air gravity anomalyfield provided the 'asic data for producing

the W*+ 22 gravimetric geoid. 5lso, a geoid referenced to the W*+ 22 Ellipsoid was derived

from availa'le astrogeodetic data to provide a detailed representation of limited land areas.

The United States Department o Deense World Geodetic

System !"72

5fter an e9tensive effort e9tending over a period of appro9imately three years, the

1epartment of 1efense World *eodetic +ystem !"3% was completed. +elected satellite,

surface gravity and astrogeodetic data availa'le through !"3% from 'oth 1o1 and nonA1o1

sources were used in a 0nified W*+ +olution (a large scale least suaresad>ustment). The

results of the ad>ustment consisted of corrections to initial station coordinates and coefficients

of the gravitational field.

The largest collection of data ever used for W*+ purposes was assem'led, processed and

applied in the development of W*+ 3%. oth optical and electronic satellite data were used.

The electronic satellite data consisted, in part, of 1oppler data provided 'y the 0.+. avy and

cooperating nonA1o1 satellite tracking stations esta'lished in support of the avy:s

avigational +atellite +ystem (++). 1oppler data was also availa'le from the numerous

sites esta'lished 'y *E=DEIJE8+ during !"3! and !"3%. 1oppler data was the primary data

source for W*+ 3% (Figure /#). 5dditional electronic satellite data was provided 'y the

+ED=8 (+euential Dollation of 8ange) Euatorial etwork completed 'y the 0.+. 5rmy in

!"3&. =ptical satellite data from the Worldwide *eometric +atellite Triangulation rogram

was provided 'y the DA$ camera system (Figure /"). 1ata from the +mithsonian

5strophysical ='servatorywas also used which included camera (aker unn) and some

laser ranging.

1oppler satellite ground stations providing data for W*+ 3% development
http://en.wikipedia.org/wiki/Gravity_anomalyhttp://en.wikipedia.org/wiki/Gravity_anomalyhttp://en.wikipedia.org/wiki/Least_squareshttp://en.wikipedia.org/wiki/Smithsonian_Astrophysical_Observatoryhttp://en.wikipedia.org/wiki/Smithsonian_Astrophysical_Observatoryhttp://en.wikipedia.org/wiki/Schmidt_camera#Baker-Nunnhttp://en.wikipedia.org/wiki/File:WORLDWIDE_GEOMETRIC_SATELLITE_TRIANGULATION_NETWORK,_BC-4_CAMERAS.GIFhttp://en.wikipedia.org/wiki/File:DOPPLER_SATELLITE_GROUND_STATIONS_PROVIDING_DATA_FOR_WGS_72_DEVELOPMENT.GIFhttp://en.wikipedia.org/wiki/File:DOPPLER_SATELLITE_GROUND_STATIONS_PROVIDING_DATA_FOR_WGS_72_DEVELOPMENT.GIFhttp://en.wikipedia.org/wiki/Gravity_anomalyhttp://en.wikipedia.org/wiki/Least_squareshttp://en.wikipedia.org/wiki/Smithsonian_Astrophysical_Observatoryhttp://en.wikipedia.org/wiki/Smithsonian_Astrophysical_Observatoryhttp://en.wikipedia.org/wiki/Schmidt_camera#Baker-Nunn


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Worldwide geometric satellite triangulation network, DA$ cameras

The surface gravity field used in the 0nified W*+ +olution consisted of a set of $!& !&H

!&H eual area mean free air gravity anomalies determined solely from terrestrial data. This

gravity field includes mean anomaly values compiled directly from o'served gravity datawherever the latter was availa'le in sufficient uantity. The value for areas of sparse or no

o'servational data were developed from geophysically compati'le gravity appro9imations

using gravityAgeophysical correlation techniues. 5ppro9imately $4 percent of the $!& mean

free air gravity anomaly values were determined directly from o'served gravity data.

The astrogeodetic data in its 'asic form consists of deflection of the vertical components

referred to the various national geodetic datums. These deflection values were integrated into

astrogeodetic geoid charts referred to these national datums. The geoid heights contri'uted to

the 0nified W*+ +olution 'y providing additional and more detailed data for land areas.

Donventional ground survey data was included in the solution to enforce a consistent

ad>ustment of the coordinates of neigh'oring o'servation sites of the DA$, +ED=8, 1opplerand akerAunn systems. 5lso, eight geodimeter long line precise traverses were included for

the purpose of controlling the scale of the solution.

The 0nified W*+ +olution, as stated a'ove, was a solution for geodetic positions and

associated parameters of the gravitational field 'ased on an optimum com'ination of

availa'le data. The W*+ 3% ellipsoid parameters, datum shifts and other associated constants

were derived separately. For the unified solution, a normal euation matri9 was formed 'ased

on each of the mentioned data sets. Then, the individual normal euation matrices were

com'ined and the resultant matri9 solved to o'tain the positions and the parameters.

The value for the semima>or a9is (a) of the W*+ 3% Ellipsoid is 2 /3# !/4 meters. The

adoption of an aAvalue !& meters smaller than that for the W*+ 22 Ellipsoid was 'ased on

several calculations and indicators including a com'ination of satellite and surface gravity

data for position and gravitational field determinations. +ets of satellite derived station

coordinates and gravimetric deflection of the vertical and geoid height data were used to

determine localAtoAgeocentric datum shifts, datum rotation parameters, a datum scale

parameter and a value for the semima>or a9is of the W*+ Ellipsoid. Eight solutions were

made with the various sets of input data, 'oth from an investigative point of view and also

'ecause of the limited num'er of unknowns which could 'e solved for in any individual

solution due to computer limitations. +elected 1oppler satellite tracking and astroAgeodetic

datum orientation stations were included in the various solutions. ased on these results andother related studies accomplished 'y the Dommittee, an aAvalue of 2 /3# !/4 meters and a

flattening of !@%"#.%2 were adopted.

In the development of localAto W*+ 3% datum shifts, results from different geodetic

disciplines were investigated, analy


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In the early !"#&s the need for a new world geodetic system was generally recogni


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The longitude positions on W*+ #$ agree with those on the olderorth 5merican 1atum

!"%3at roughly #4H longitude west, in the eastAcentral 0nited +tates.

Updates and ne$ standards

The latest ma>or revision of W*+ #$ is also referred to as OEarth *ravitational -odel !""2O(E*-"2), first pu'lished in !""2, with revisions as recent as %&&$. This model has the same

reference ellipsoid as W*+ #$, 'ut has a higherAfidelity geoid (roughly !&& km resolution

versus %&& km for the original W*+ #$).

-any of the original authors of W*+ #$ contri'uted to a new higher fidelity model, called

E*-%&.!&This new model will have a geoid with a resolution approaching !& km,

reuiring over $.2 million terms in the spherical e9pansion (versus !/&,/!3 in E*-"2 and

/%,343 in W*+ #$).
http://en.wikipedia.org/wiki/North_American_Datumhttp://en.wikipedia.org/wiki/North_American_Datumhttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/EGM96http://en.wikipedia.org/wiki/EGM96http://en.wikipedia.org/w/index.php?title=EGM2008&action=edit&redlink=1http://en.wikipedia.org/wiki/World_Geodetic_System#cite_note-9http://en.wikipedia.org/wiki/World_Geodetic_System#cite_note-9http://en.wikipedia.org/wiki/North_American_Datumhttp://en.wikipedia.org/wiki/North_American_Datumhttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/EGM96http://en.wikipedia.org/wiki/EGM96http://en.wikipedia.org/w/index.php?title=EGM2008&action=edit&redlink=1http://en.wikipedia.org/wiki/World_Geodetic_System#cite_note-9

World Geodetic System 84

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