Talk:World Geodetic System
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[edit] Text from Geodesy for the Layman
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.
[edit] Ellpsoids not Geoids?
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)
- 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)
[edit] system,datum
geodetic system == geodetic datum, need to clatify that. The word "datum" is used in GPS geceivers, so it is very important.
[edit] EGM06
"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)
[edit] WGS 64??
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)
[edit] Link to Mercury
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)
[edit] Zero meridian
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)
- Found it out myself and put it in the article. --Abdull 12:11, 3 May 2007 (UTC)
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)
[edit] relationship to TRANSIT / NAVSAT / NNSS
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)
