Talk:Geographic coordinate system

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Graticule[edit]

The DAB page Graticule says the term only applies to the Geographic coordinate system. Why doesn't it also apply to Geodetic coordinate system, or any other map coordinate system? SharkD  ☎  20:56, 10 August 2018 (UTC)[reply]

Are you suggesting that a geodetic coordinate system is not a geographic coordinate system? “Graticule” specifically does not apply to the rectangular grid systems imposed on top of a map. Strebe (talk) 22:02, 10 August 2018 (UTC)[reply]

Spelling[edit]

I conclude the article uses British spelling based on the word "metre" being introduced on 27 October 2017. Jc3s5h (talk) 12:11, 3 May 2019 (UTC)[reply]

There was no edit on October 27, 2017, and in any case, the article was written in 2002 in US English (“center”; no mention of “meter/metre”), not in 2017. Usage has been incorrectly mixed at odd intervals since. Strebe (talk) 16:36, 3 May 2019 (UTC)[reply]

Clarifications to Geodetic Datum section[edit]

I've edited the Geodetic datum section to try and make it clearer. It's my first Wikipedia edit, so apologies if I have gone about this the wrong way - please feel free to revert.

Specifically, I wanted to try and improve the following text

Coordinates from the mapping system can sometimes be roughly changed into another datum using a simple translation. For example, to convert from ETRF89 (GPS) to the Irish Grid add 49 meters to the east, and subtract 23.4 meters s from the north.[7] More generally one datum is changed into any other datum using a process called Helmert transformations.
  • There is a link to "translation" in the linguistic sense, rather than the geometric one, which I assume is a mistake
  • A reader could assume that you can add meters to an ETRF89 latitude and longitude. The original source [7] makes clear that there is first a transverse Mercator projection using Irish Grid parameters to turn the lat/lon into Eastings and Northings (which you can add metres to), but that context is lost here.
  • The phrase "ETRF89 (GPS)" could give the impression that GPS is based on ETRF89. The original source [7] uses the parenthetical reference to indicate locations that were derived from a GPS receiver, but this context is lost here.

For me, the key point of the paragraph is to indicate that your "local" datum might not be the one used by your GPS receiver, and you may need to do a datum transformation, which might be a trivial translation but probably isn't. I have attempt to edit it to keep this intent while addressing the issues above. I felt some of the detail (the number of metres you add to an Irish Grid northing, how many parameters there are in a Helmert transformation) was unnecessary for the purposes of understanding what a datum is, so I trimmed it out.

I hope this is an improvement and that I've gone about this the right way. Please correct and educate me if not!

--Mcanterb (talk) 08:39, 4 July 2019 (UTC)[reply]

Intro sentence - spherical coordinates[edit]

The first sentence is a little confusing about the relationship to spherical coordinate systems:

A geographic coordinate system is a coordinate system that enables every location on Earth to be specified in three coordinates, using mainly a spherical coordinate system.

What does "mainly" mean here? The article on Spherical coordinate system says that a geographic coordinate system is different than a spherical one. -Pgan002 (talk) 13:57, 19 October 2019 (UTC)[reply]

Too many reverts[edit]

I see a bit too many reverts, which I suggest end. There are some useful and unuseful bits, so I don't want to add add another revert. Here are a few notes:

  • Use of en dash for "west–east" is correct (MOS:ENDASH), so keep these edits.
  • There is no primary English variation for this article. Not sure what's best: use all US English, use all British English, or mixed, as this is a globally-focused article. I think it is OK to have it mixed in context, as it was before. So use British English for "but neighbouring Scotland" and American English for "cartographical organization include the North American Datum". More on this MOS:ENGVAR.
+mt 21:00, 25 March 2020 (UTC)[reply]
The top of the talk page contains a US English template. Presumably the UK spelling snuck in after the template was added.Jc3s5h (talk) 21:24, 25 March 2020 (UTC)[reply]
Thanks, I normally look for {{Use American English}} on the main article, but I see this now on the Talk page. This is fine with me. +mt 23:27, 25 March 2020 (UTC)[reply]

Figure is wrong[edit]

The figure with the caption "Earth centered, Earth fixed coordinates in relation to latitude and longitude" is wrong -- since this is for an ellipsoid, the radius vector $r$ should not pass through the center of mass of the ellipsoid. See here: https://en.wikipedia.org/wiki/Geographic_coordinate_conversion#/media/File:Geodetic_latitude_and_the_length_of_Normal.svg — Preceding unsigned comment added by 205.204.46.102 (talk) 01:45, 30 August 2020 (UTC)[reply]

The diagram is for ECEF, which is not geodetic coordinates. As stated in the article,

The Earth-centered Earth-fixed (also known as the ECEF, ECF, or conventional terrestrial coordinate system) rotates with the Earth and has its origin at the center of the Earth.

Strebe (talk) 03:14, 31 August 2020 (UTC)[reply]

Rename??[edit]

The name of this page can be confusing, as the specific term GCS is commonly used only for the spherical (lat/lon) coordinates, as opposed to planar or projected coordinate systems (e.g., in ArcGIS and some textbooks). The generic term is just "coordinate system" in geography, so perhaps it should be Coordinate System (Geography), with a section or separate page focusing on GCS (lat/lon). That said, I've always thought such a co-option of the generic term GCS for one type is unfortunate, but it is not my decision. Maybe we should just follow the crowd and start calling lat/lon "GPS coordinates" ;-) Bplewe (talk) 16:01, 22 November 2021 (UTC)[reply]

Oppose. Bplewe has not offered sufficient proof, with citations to reliable sources, that the term "geographic coordinate system" only applies to latitude and longitude, and excludes other terrestrial coordinates such as projected coordinates, Cartesian coordinates coordinates etc. Also, it is not clear tom me that "Coordinate System (Geography)" would be any better than "Geographic coordinate system".
Support. “Geographic coordinate system” as used in GIS these days refers to spherical coordinates with a datum. I think this is an Esri convention that has pretty much taken over. The literature, historically, refers to “geographic(al) coordinates” (without “system”) to mean latitude and longitude; no such term as “geographical coordinate system” seems to have been in common use before GIS. Yes, we need references, but the reference will support this change. Strebe (talk) 19:11, 22 November 2021 (UTC)[reply]
It's not clear that we should decide only on the basis of GIS nomenclature. Some other points of view are astronomy and geography as an academic subject. Looking around, I discovered that Earth-centered, Earth-fixed coordinate system essentially covers (or should cover) the same material, but is a bit more astronomy-oriented. The two articles should probably be merged. Jc3s5h (talk) 21:51, 22 November 2021 (UTC)[reply]
If the term “geographic coordinate system” was not defined before it came into use in GIS, and is in use nowhere else, then I think we should decide “only on the basis of GIS nomenclature”. The closest I can find routinely in the literature before GIS is “geographic coordinate(s)”, which always seems to refer to latitude/longitude. I don’t think ECEF the should get merged with this one. The ECEF article is woefully incomplete and inadequate; I think it should get fleshed out. Strebe (talk) 01:55, 23 November 2021 (UTC)[reply]
I totally agree with not changing the terminology solely because ArcGIS does so, and thanks Daan for making me do my homework (and also thanks for being the watchdog over this subdiscipline, every one should have someone as conscientious). There does seem to be an emerging consensus, encapsulated in EPSG, ISO 19111 and the corresponding OGC AS-2, and I would propose that we should conform to their terminology as the baseline. As annoyed as I am about the confusing way that ArcGIS uses these terms in its interface, it does technically conform to these standards. These all define the following (OGC AS-2 Section 9):
  • Coordinate system is a generic term for a framework for measuring locations, not necessarily geographic
  • Coordinate reference system is a standardized coordinate system for measuring geographic locations, a coordinate system along with a choice of horizontal datum. Spatial reference system is also used a lot here.
  • Geographic CRS measures location using ellipsoidal coordinates (lat/lon on a choice of ellipsoid model, maybe + HAE)
  • Geocentric CRS = Earth Centered Earth Fixed
  • Projected CRS measures location on a planar surface created by a map projection
  • and a bunch of others including local-context "Engineering CRS", image coordinates, etc.
So my revised proposal is to improve Spatial reference system to be the overall umbrella, and focus this page on lat/lon+datum, with the existing title. Grid reference system should probably be revised slightly to conform; should it be renamed to Projected Coordinate System?Bplewe (talk) 00:33, 24 November 2021 (UTC)[reply]

Refocused[edit]

Since there was no objection to my proposal, I have refocused this page with respect to Spatial reference system, Grid reference system, and Earth-centered, Earth-fixed coordinate system, so that this page focuses specifically on latitude/longitude, which is how the term is used in the international standards mentioned above. It could still use some improvement, though. Bplewe (talk) 02:44, 18 December 2021 (UTC)[reply]

Geography[edit]

What is meant by geographic coordinate system?who introduced it? 2405:EC01:1001:2B61:FEF:BAB5:6097:67FC (talk) 04:52, 12 June 2022 (UTC)[reply]

@2405:EC01:1001:2B61:FEF:BAB5:6097:67FC its a worldwide corrdinates and idk either who introduced it 2601:680:8300:3870:ACD0:3995:CC1D:3CEF (talk) 05:28, 25 January 2024 (UTC)[reply]

North South East West[edit]

One often sees e.g. +/-Y° and +/-X° instead of °N/S and °E/W. If there are one or more standards for this, I think it might be helpful to discuss this topic on the page. 142.92.29.46 (talk) 19:05, 12 February 2024 (UTC)[reply]

Good point. Strebe (talk) 23:04, 12 February 2024 (UTC)[reply]
Do you have some example sources? –jacobolus (t) 23:46, 12 February 2024 (UTC)[reply]
Not off the top of my head. But I have encountered it in the past. I came here looking to confirm which is "standard" (I think + is usually N and E) and found nothing. 142.92.29.45 (talk) 14:35, 13 February 2024 (UTC)[reply]
Found one. Look at the +/- values given for lat/lon here:
https://geopandas.org/en/stable/docs/reference/api/geopandas.points_from_xy.html 142.92.29.45 (talk) 14:59, 13 February 2024 (UTC)[reply]