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Text from Geodesy for the Layman

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This text is taken from the public domain resource Geodesy for the Layman at http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/TR80003E.HTM#ZZ11 -- please Wikify as necessary. This document was written in 1984 and may need to be updated.

"(Figure 38)" and "(Figure 39)" are quoted, which is not relevant for a Wikipedia article. Gfombell (talk) 16:29, 9 October 2018 (UTC)[reply]

Ellpsoids not Geoids?

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Aren't these all ellipsoids and not geoids? These WGSxx ellipsoids seem like the best fitting ellipsoids for the geoids, but they are still theoretical surfaces and not gravity based. DavidForrest 01:56, 4 April 2006 (UTC)[reply]

The WGS84 and EGM96 define both an ellipsoid and a geoid, with the ellipsoids essentially "first order" geoids. The EGM96 geoid is definitely gravity based. Unfortunately, the ellipsoid was not changed from the earlier WGS84 parameters because this would have seriously impacted the operation of GPS. MFago 14:05, 4 April 2006 (UTC)[reply]

system,datum

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geodetic system == geodetic datum, need to clatify that. The word "datum" is used in GPS geceivers, so it is very important.

"datums"? Isn't "data" the plural of "datum"? — Preceding unsigned comment added by 2607:FCC8:BD57:5300:A81E:5374:4250:9951 (talk) 11:31, 9 January 2018 (UTC)[reply]

Not in this context. Strebe (talk) 15:25, 9 January 2018 (UTC)[reply]

EGM06

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"This new model will have a geoid with a resolution approaching 10 km, requiring over 4.6 million terms in the spherical expansion (versus 130,317 in EGM96 and 32,757 in WGS 84)."

The resolution of 10 km is wrong. Perhaps it is 10 cm? Also, it would be good to include the maximum spherical harmonic degree of the EGM96 and EGM06 models (360 vs. 2160?). Lunokhod 19:44, 13 November 2006 (UTC)[reply]

WGS 64??

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In the second paragraph was that previous versions of WGS were wgs 72, wgs 64 and wgs 60. But in the rest of the article and also in other sources in not any wgs 64, but wgs 66 - so i will correct it, ok? --Stardust 00:11, 2 April 2007 (UTC)[reply]

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The the astronautic Mercury datum links to Mercury (planet). I'm fairly confident the planet is irrelevant here so I'll remove the link. I assume it should link to Project_Mercury but I'm not confident enough fill that link in. EdDavies 20:10, 30 April 2007 (UTC)[reply]

Zero meridian

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The longitude positions on WGS84 agree with those on the older North American Datum 1927 at roughly 85° longitude west, in the east-central USA. By contrast, the zero meridian of WGS84 is about 100 metres east of the Prime Meridian at Greenwich, UK.

North American Datum 127 says it is based on a geodetic base point in Meades Ranch, Kansas. So what I don't understand is - why happens WGS84 to be approximately 100 meters apart from the traditional Prime Meridian in Greenwich? What is the definition of the WGS84's zero meridian? --Abdull 11:27, 3 May 2007 (UTC)[reply]

Found it out myself and put it in the article. --Abdull 12:11, 3 May 2007 (UTC)[reply]

WGS 84 uses the zero meridian as defined by the Bureau International de l'Heure,[1] which was defined by compilation of star observations in different countries. The mean of this data caused a shift of about 100 metres east away from the Prime Meridian at Greenwich, UK.[2]

The WGS84 Zero Meridian (IRTF) link incorrectly points to the unrelated Prime Meridian page.

Is it not the case that a discrepancy in originally defining the Meades Ranch datum's longitude, was then propogated into the WGS84 TRF, resulting in the differences between Greenwich & WGS84 ? http://www.ngs.noaa.gov/faq.shtml#WhatDatum

The info on http://en.wikipedia.org/wiki/WGS84 is also incorrect. Basys (talk) 14:39, 17 May 2008 (UTC)[reply]

relationship to TRANSIT / NAVSAT / NNSS

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After reading through this page, and also looking through the Transit (satellite) page, I noticed that while 'Navy Navigation Satellite System' is mentioned on the WGS84 page, no link is provided to the TRANSIT page. I notice that searching wikipedia for 'NAVSAT' or 'TRANSIT' will take you to the appropriate page, but searching for 'NNSS' does not. I don't know quite enough about wikipedia to know how to make the NNSS acronym take you to that page, but perhaps it should at least be linked from this page? Also, I have found a lot of great background information on both WGS84 and TRANSIT / NAVSTAR / NNSS in the following source: 

Seeber, G. (2003). Satellite Geodesy (2nd ed.). Berlin, Germany: Walter de Gruyter.

Much of the book can be viewed on-line through Google Books by searching for 'satellite geodesy TRANSIT' or 'satellite geodesy WGS84' ChrisTracy (talk) 03:21, 10 December 2007 (UTC)[reply]

NNSS fixed. -- SEWilco (talk) 04:05, 10 December 2007 (UTC)[reply]

Notation

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Could any kind person with more knowledge of WGS 84 explain the notation of a coordinate in WGS 84? (with °, ′ and ″ symbols). I really miss this part in the article. Cristan (talk) 12:33, 4 March 2009 (UTC)[reply]

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The word "collocation" is used in the article in the section called "A new World Geodetic System: WGS 84". I was going to Wikilink "collocation" but I am not qualified to decide if the link should be to the "Collocation (remote sensing)" article or the "Collocation method" article. I request that someone with expertise wrap some braces around "collocation" and point the link in the proper direction. Thank you. O'Dea (talk) 00:04, 27 August 2010 (UTC)[reply]

Accuracy of a and b ?

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Why is "a" (major radius) quoted as = 6,378,137 m (which implies an accuracy +/- 1m) and "b" (minor radius) quoted as 6,356,752.314 245 m (which implies an accuracy of +/- 0.001 mm)? Surely they should both be quoted to the same accuracy? Is "a" supposed to be 6378137.000000 m, or is "b" supposed to be 6356752 m?

Both "a" and "b" should have citations. — Preceding unsigned comment added by K153 (talk • contribs) 12:57, 7 January 2011 (UTC)[reply]

"a" is exact; "b" is exactly (297.257223563/298.257223563) times a. Tim Zukas (talk) 02:11, 14 November 2011 (UTC)[reply]

EGM96 is NOT a Geoid

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Presently WGS 84 uses the 1996 Earth Gravitational Model (EGM96) geoid, revised in 2004. This geoid defines the nominal sea level surface by means of a spherical harmonics series of degree 360 (which provides about 100 km horizontal resolution).[8] The deviations of the EGM96 geoid from the WGS 84 reference ellipsoid range from about -105 m to about +85 m.[9] EGM96 differs from the original WGS 84 geoid, referred to as EGM84.

EGM96 is wrongly referred to as a geoid.

It is a model of geo-potential (gravimetric) variation, and, as such, may be used to correct the ellipsoidal height as determined by the GPS system, to an orthometric (geoidal) height, commonly referred to as 'above mean sea level'. Other than in this context, it has nothing to do with WGS.

The error values quoted have nothing to do with EGM96, but refer to the error between the ellipsoidal height derived by the GPS system and the geoidal height. The EGM96 parameters are commonly used to remove this error, but leave a residual error in the region of 150 to 750mm, depending on the actual height above mean sea level, local topography, etc. The higher order EGM08 database, which has superceded EGM96, claims a residual error somewhere in the region of 20mm.

If you decide to retain this section, I'd recommend removing the meaningless part about 'spherical harmonics of degree 360'. The ACTUAL definition is included in the linked page if anyone feels it is worth keeping. Although (once corrected) it is a true statement, referring to the method of computation of the mathematical model defined by the EGM96 data, I fail to see what it adds to anyone's understanding of WGS. --62.3.65.20 (talk) 13:06, 13 March 2011 (UTC)[reply]

history/helmert's book

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the original title is "Die mathematischen und physikalischen Theorien der Höheren Geodäsie" not "Mathematische und Physikalische Theorien der Physikalischen Geodäsie" —Preceding unsigned comment added by 88.72.180.224 (talk) 18:32, 15 May 2011 (UTC)[reply]

WGS84 invalid after 2010?

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'The latest revision is WGS 84 (dating from 1984 and last revised in 2004), which will be valid up to about 2010'

Happy 2012 - What happened in 2010? --129.234.252.67 (talk) 13:02, 19 January 2012 (UTC)[reply]

2016 here, still cannot find an answer to this. Some sites have started saying that WGS84 *was* valid until 2010, though, yet still without an explanation. — Preceding unsigned comment added by 2620:101:F000:702:7071:F151:BB07:4F9 (talk) 01:29, 19 December 2016 (UTC)[reply]

Example coordinates?

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If this is even a sensible question - would examples be useful? e.g. where major cities would be in this system - David Gerard (talk) 09:22, 29 May 2014 (UTC)[reply]

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The bot classified http://earth-info.nga.mil/GandG/images/ww15mgh2.gif as dead when it is actually working just fine. I suspect this is because sites in the .mil top level domain are reputed to refuse connections from IP addresses outside the US. I have opened Phabricator task T174887. Jc3s5h (talk) 13:03, 3 September 2017 (UTC)[reply]

Coordinates

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When one uses a World Geodetic System to define or measure the position of some point, how is the position typically expressed? Is it terms of altitude above sea level, latitude, and longitude? If so, can we make that more prominent in the article? 74.76.180.38 (talk) 15:26, 21 September 2017 (UTC)[reply]


Most common would be latitude, longitude, and height above or below the reference ellipsoid. Latitude and longitude could be expressed as decimal degrees, degrees and decimal minutes, or degrees, minutes & seconds. Ellipsoid height is not the same as height above or below sea level. The idea of giving some examples of how it's typically expressed is good.
Another possible way to express a location would be in terms of x, y, and z coordinates. The origin would be the center of the Earth, the positive x axis would begin at the center of the earth and pass through the point on the reference ellipsoid with 0° latitude and 0° longitude. The positive z axis begins at the center of the earth and passes through the point on the reference ellipsoid with 90° latitude. The y axis is in the direction it has to be to form a right-handed coordinate system. Jc3s5h (talk) 16:13, 21 September 2017 (UTC)[reply]

Primary Reference Does Not Load Easily

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The primary reference https://earth-info.nga.mil/GandG/update/index.php?dir=wgs84&action=wgs84 for this article does not load cleanly in Chrome as of June 2019 because of disagreements between earth-info.nga.mil and Google as to what constitutes a valid TLS certificate. — Preceding unsigned comment added by 165.228.69.43 (talk) 01:45, 19 June 2019 (UTC)[reply]

Image caption (handheld at Greenwich)

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The caption on the image of the handheld GPS receiver at Greenwich states that 0.089 arc minutes equals 16.5 cm. An arc minute is about 1.8 km at the equator, so a ballpark figure would be 900 m at Greenwich, so 0.1' would be about a hundred meters? 213.113.118.138 (talk) 15:52, 19 March 2021 (UTC)[reply]

This is wrong. It was inserted in this edit by User:31.124.153.159. I have undone the change. There are a number of places you can compute what it really is, including a utility at the National Geodedic Survey. It is about 103 m. Jc3s5h (talk) 17:25, 19 March 2021 (UTC)[reply]

Mention meters too

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Greenwich meridian is 0.089 arcminutes (or 5.34 arcseconds) west to the WGS 84 datum

That's great, but mention how many meters at that latitude that is too. E.g., 103. Jidanni (talk) 13:07, 15 June 2021 (UTC)[reply]

Yes, 0.089 arcminutes is 103.053 m for the GPS receiver at 51d28.675'N. However, the actual meridian is closer to 102 m, as stated (and referenced) elsewhere in the article. So it's a bit awkward to present two values. I would prefer the caption to only state what's shown in the photo. +mt 00:29, 16 June 2021 (UTC)[reply]
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Should the External Links section include the second edition of the WGS 84 standardization document (published in 1991)? The section also includes a link to the most recent version of this document (published in 2014). Does this meet the burden described in WP:EL?

The older document contain a description of the original Earth Gravitational Model for WGS 84, which no longer appears in the latest version (later versions of EGM are documented independently). There is a separate article with details about the Earth Gravitational Model though; perhaps the link is better suited for that article.

We should also consider WP:ELDUP, perhaps for both of the links here.

(Note: the link was erroneously labeled as being to the Third Edition. I have modified the text to reflect what it is actually pointing to.) Davidpward (talk) 00:41, 27 December 2022 (UTC)[reply]

Any ambiguity in application of the WP:EL guidelines ought to go in favor of inclusion, in my opinion. This is not frivolous or tendentious material, so it’s hard for me to imagine exclusion being more valuable than inclusion. Thanks for all the diligence. Strebe (talk) 17:40, 27 December 2022 (UTC)[reply]
For context there is a big discussion here. https://en.wikipedia.org/wiki/User_talk:Valery_Zapolodov#WGS_84_Standard Valery Zapolodov (talk) 08:41, 28 December 2022 (UTC)[reply]

Error in gravitational constant

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The gravitational constant (GM) is shown as

GM = 3986004.418×1014 m3/s2

It should be

GM = 3.986004418×1014 m3/s2 74.142.99.82 (talk) 12:25, 23 June 2023 (UTC)[reply]

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