Talk:Earth-centered, Earth-fixed coordinate system

Text and/or other creative content from this version of Geocentric coordinates was copied or moved into ECEF with this edit on 20 August 2018 (UTC). The former page's history now serves to provide attribution for that content in the latter page, and it must not be deleted as long as the latter page exists.

ECEF and relativity

Isn't a single coordinate system like ECEF compatible with relativity? If this system is used when does one need Lorentz transformations? — Preceding unsigned comment added by 2A02:A471:E20D:1:6918:75C:73FD:16A3 (talk) 17:41, 15 January 2024 (UTC)[reply]

z-axis definition

Is this definition really correct? Isn't the z-axis coincident with the eart's axis of rotation rather than parallel to it?

Jlhollin (talk) 20:30, 3 February 2009 (UTC)[reply]

Those two definitions basically mean the same thing; lines that are coincident are also parallel. The two pieces of information that are needed to define the z-axis in this frame are its orientation (parallel to the rotation axis of the Earth) and the direction in which it is positive-- north. The fact that the origin lies at the mass center of the Earth indicates that it is coincident with the rotation axis. Or at least, just about; there's presumably some variation in the location of the mass center of the Earth, and in its rotation axis, but these are not usually considered. siafu (talk) 21:48, 3 August 2009 (UTC)[reply]

Yoepp (talk) 14:32, 15 March 2010 (UTC) Parallel and coincident are not the same thing. Lines can be parallel and not coincident. It would be clearer to use "coincident".[reply]

It is incorect, but not semanticly. The z-axis of ECEF does not coincide with the true rotation axis but rather with the mean rotation axis. The instantaneous Earth rotation axis moves with respect to the Earth surface due to a phenomemon known as polar motion. I will correct the definition.--Shlomi.israel (talk) 05:12, 7 December 2010 (UTC)[reply]

"Used for GPS"

I'm removing this particular line in the article, as its not clear what is meant by this. GPS receivers can be configured to provide location information in various coordinate frames, not limited to ECEF, and the broadcast ephemerides are definitely not in ECEF themselves. If anything, WGS84 has the greater claim to being "used" by GPS. siafu (talk) 21:48, 3 August 2009 (UTC)[reply]

The current article includes this confusing line:

"The ECEF that is used for the Global Positioning System (GPS) is the geocentric WGS 84, which currently includes its own ellipsoid definition."

WGS literally stands for "World Geodetic System" (Wikipedia article: World Geodetic System), so I don't know why this author claims that it's a geocentric system. Unless they are trying to suggest that if you want to use an ECEF reference system with GPS data, that you should use the WGS ellipsoid?

I'm not an expert in this field so I don't really know what they are trying to say, or how to fix it, but I do know that this line as written contradicts what seems to be basic common knowledge about WGS84. 66.31.63.68 (talk) 16:30, 3 February 2023 (UTC)[reply]

I think they meant that GPS uses the WGS84 ellipsoid, but geocentric coordinates therewith? The former would be EPSG 4326, and the latter would be EPSG 4978. I have no idea if this claim is true, but it is one way to interpret the sentence as written. 66.31.63.68 (talk) 18:48, 3 February 2023 (UTC)[reply]

How Fixed is "Fixed"?

Since the z-axis is the mean rotation axis a point anchored on the Earth's surface will move around at least because the Earth's rotation axis is moving around. But what are the other reasons for a monument anchored to the Earth's crust will change position in this coordinate system? Solid Earth tides, varying rotation rate (does the x-axis follow the mean rotation or the true rotation?), anything else? It would be helpful to precisely define what exactly is fixed. — Preceding unsigned comment added by Cuhlik (talk • contribs) 18:29, 25 June 2014 (UTC)[reply]

Only one ECEF system?

This article makes it sound like there is only one ECEF system, and that its z axis "does not coincide exactly with the instantaneous earth rotational axis". Is that really true, though? Earth-centered inertial mentions "Earth-fixed frames" in plural, and the link "ECEF Datum transformation" (in the ECEF article) even states that it is talking about a system whose z axis pierces the north pole. —Bromskloss (talk) 22:09, 7 August 2016 (UTC)[reply]

It is really true; ECEF is a specific coordinate system. The fact that it "does not coincide exactly with the instantaneous Earth rotational axis" is due to the fact that said axis is constantly moving itself due to a number of small effects (precession, nutation, true polar wander, etc.). ECEF is not fixed to the rotation axis of the Earth, *per se*, but the *North pole* defined as the international reference pole (mentioned in the article); this point, unlike the rotation axis, is fixed to a point on the surface of the Earth. siafu (talk) 20:24, 8 August 2016 (UTC)[reply]

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Diagram needs updating

The diagram shows the ray that points towards the ECEF point on the surface of the ellipsoid does not originate from the center of the earth. In WGS84 at least, the center of the earth is defined to be the center of mass, and a WGS84 geoid to ECEF conversion will reuse this center as the center of the (x, y, z) coordinate system. — Preceding unsigned comment added by 205.204.46.102 (talk) 23:12, 27 August 2020 (UTC)[reply]

I replaced the image with a svg version which seems to be correct.―― Phoenix7777 (talk) 23:38, 27 August 2020 (UTC)[reply]

png version
svg version

The svg version is wrong (for an ellipsoid)! The line showing the latitude has a z-intercept = $-{\frac {ae^{2}\sin ^{2}\varphi }{\sqrt {1-e^{2}\sin ^{2}\varphi }}}$ . This is not the origin unless $e=0$ Chuckage (talk) The png version leaves something to be desired as well. A better version would be without p and r, since neither are used in the definition. Chuckage (talk)