Talk:Geodesy/Archive 1

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Archive 1

Archive 2

Data is the plural of datum

At the end of the introductory paragraph the word datums is used instead of data, which is the plural of datum. Data is a very common word in English, so this is not an obscure Latin plural. I am not an expert in this field, so I'm writing this here(I am still not sure if I'll correct it), in order to be respectful of the authors, in case there is a reason for the exotic plural. Jergas (talk) —Preceding undated comment added 07:11, 12 March 2017 (UTC)

"Datums" is the normal usage in this field, see Geodetic datum. cffk (talk) 08:13, 12 March 2017 (UTC)

The plural of "datum" in geodesy is conventionally "datums."

"For a group of statistical references, the plural form is data: as geographic data for a list of latitudes and longitudes. Where the concept is geometrical and particular, rather than statistical and inclusive, the plural form is datums, as, for example, two geodetic datums have been used in this country in recent years."
— Hugh Mitchell, Definitions of Terms used in Geodetic and other Surveys, 1948

Ryan Hardy (talk) 02:18, 21 March 2017 (UTC)

Earth's magnetic field

I am not sure that the Earth's magnetic field is the subject of geodesy. Don't think so.

No, it isn't. Geodesists make just use of it, but it belongs to Geophysics or Potential theory. --Geof 05:27, 27 September 2006 (UTC)

Reference ellipsoid

I created 'reference ellipsoid'. Some of the stuff in this page should IMO go there.

Traditional Surveys vs Space Geodesy

I did not write the (unsigned) item above.

It is my impression that many datums are still the result of surveys of limited geographic regions (with classical instruments like the theodolite and plumb bob) and that they often do not patch together very well. While there is the attempt to reference them to an ellipsoid, the use of the plumb bob or equivalent references them to the geoid, which then must be further referenced to a chosen ellipsoid. I suggest that the "datums" article be filled out some more with examples - perhaps with newer ones determined by spacecraft - and that it be OWN3D! separate. There are already so many ellipsoid models (WGS84, Fischer, Mercury, Everest, .....) and so many datums that one might do best to add some table of the most used of these in each article; putting them together could result in a hodgepodge. Pdn 23:40, 19 July 2005 (UTC)

This sentance doesn't make sense. I don't know anything about geodesy, or i'd fix it myself. "Geodesy is primarily concerned with positioning and the gravity field and geometrical aspects of their temporal variations, although it can also include the study of the Earth's magnetic field." 169.237.97.2 00:19, 18 February 2006 (UTC)

@ Pdn: The different reference of terrestrial and space based Geodesy is a problem and a chance, too. Terrestric height MUST refer to geoid, otherwise "water will flow" between points of the same height. But satellite measurements are mainly geometric and not influenced by the gravity field like the level of a theodolite. Therefore the plumb line deflections do not affect SLR-Laser or GPS measurements => the results are more accurate and can be treated on a global basis. This gives the chance to reduce all local data to a global system (if required) up to some mm..cm accuracy.
As for the different ellipsoids: some 200 exist for all countries, but in german Wiki I wrote a table of the most important de:Referenzellipsoids in 2004. You may transfer it to reference ellipsoid. If you are interested in numerical examples, it's difficult on a general basis. On the border of 2 countries, the national geodetic systems may differ by 100 or 500 m (caused by different fundamental points and their vertical deflections). But by empirical transformation formulas we can solve the "problem" up to ±1-2 cm. --Geof 05:27, 27 September 2006 (UTC)

Merge, Organize?

I am thinking about adding some info that seems to be missing from WP:

geodetic coordinates, geocentric coordiantes, ECEF coordinates etc.
geodetic height, geoid height, etc
datum conversion, 3 parameter, 7 parameter, Molodensky etc.
lists of reference ellipsoids and datums

and add some SVG diagrams to help explain everything. It looks like Datum has already been merged into Geodetic system and may be merged into this article. Geodetic vs. geocentric is covered in Lattitude but could use some pics. Any thoughts on how organize this? Rebuild the Datum article? Add to this article? Cover everything in Datum conversion? EricR 18:58, 21 March 2006 (UTC)

Diagrams are welcome, but Merging is not a good idea. The geodetic SYSTEM theory (which may be expanded, and also supplemented by international frames like ETRF/ITRS/ITRF 99-05, VLBI, plate tectonics etc.) doesn't fit to a general GEODESY article - and would make it bulky, too. If you understand german, look there (in Germany & Austria we have very active Wiki-Geodesists and the Category tree is increasing in quality). But if you really like to merge the articles, please give me a note on my german Discussion page. --Geof 05:27, 27 September 2006 (UTC)

Link to a link collection?

The newly added [1] link should be deleted, or replaced with the most useful links found on that page. I suggest deleting it, just take a look on that crap of a page. Just wanted to ask your opinion first... --V. Szabolcs 12:14, 29 September 2006 (UTC)

Spam removed. Vsmith 23:29, 29 September 2006 (UTC)

Vertical datum transformations

In the Geodetic Data section, on the subject of datum transformations, it says: "In the case of vertical datums, this consists of simply adding a constant shift to all height values." But that cannot be true, except locally. In Scandinavia, for example, the land is still rising after the last ice age, but not uniformly. Parts of north Sweden are rising by 9 millimeters per year, while south Sweden is almost still. Therefore, when shifting height values from a vertical datum of the year 1900 into a datum of the year 2000, there should be a one-meter change in north Sweden, but much less in south Sweden. --Mikael R 15:19, 20 February 2007 (UTC)

Vandalism

My friend is adding his name to list of famous surveyors in 20th century. Can someone block page from editing by unregistered users?

Images

Does anyone know of an appropriate source of freeware or otherwise to-Wikipedia-acceptable science-related images? I would like to place a more attractive image at the top of the article. The way it is right now, I think that many people who open the page get easily repelled (by that obsolete pillar photo) rather than attracted to the subject. Unfortunately, scanning through internet pages is reality of the fast-paced world we live in. --Geoeg 18:52, 10 October 2007 (UTC)

Legitimate Vincenty Implementations Deleted?

Presently, there's an external link to a JavaScript implementation of Vincenty's solution. However, I see the links I added to a Java and C# implementation have been removed. Is it policy to remove legitimate resources solely because the source also includes a blog?
http://www.gavaghan.org/blog/free-source-code/geodesy-library-vincentys-formula-java/
and
http://www.gavaghan.org/blog/free-source-code/geodesy-library-vincentys-formula/

Does anybody benefit by arbitrarily excluding two mainstream programming languages? After all, the present inclusion of JavaScript is rather specious. A scripting language is fine for ad hoc, web-based lookups, but thoroughly impractical for meaningful software applications. If some other software package fills the same need and provides Java and C# implementations, then maybe we can use that alternative. In the meantime, however, I'm not sure that anything equilvalent exists. MickeyWiki (talk) 13:17, 28 November 2007 (UTC)

That was my interpretation of WP:EL saying to avoid "Links to blogs and personal web pages, except those written by a recognized authority." I'm not familiar with the guy, but if he's a recognized authority, tell us so and then it might be OK. He looks to me like a random software consultant and blogger. Dicklyon (talk) 04:07, 29 November 2007 (UTC)

Here's the CodeProject version of the same C# code:

http://www.codeproject.com/cs/library/Vincentys_Formula.asp

CodeProject is a recognized publisher of software articles - not a blog. I have two nits with this link, however: 1) it's one degree removed from the original source, and 2) it only addresses the C# library, not the Java library. Your thoughts? MickeyWiki (talk) 04:21, 29 November 2007 (UTC)

It has been over a month with no further discussion, so I'm going to go ahead with the following changes:

1) I'll replace the C# link with the link to CodeProject. Again, I'm uncomfortable with this since it's one more level of indirection from the source material. But, it's not a blog - so that should alleviate any concerns there.

2) Because the CodeProject article does not address the Java code, I went looking for the same content on a non-blog site. I came up empty. Absent any other established Java implementation in a more favored forum, the original link seems to be the best option available.

Once again, a link to JavaScript has already been deemed legitimate, but JavaScript is wholly worthless for any meaningful Geodesy application other than simplistic web pages. Two links to the implementation in production quality programming languages, C# and Java, add meaningful value to the page. After all, few people have the skills, time, or inclination to recreate these algorithms from Vincenty's original work. Iterative mathematical formulas are inherently difficult to implement. MickeyWiki (talk) 03:35, 5 January 2008 (UTC)

Red links

This article may be getting out of control, since it now has so many red links to individuals who don't have their own Wikipedia articles. Perhaps a rule should be adopted that WP articles should be required. For example, this is rule is in effect over at List of search engines (no red links are allowed) and the resulting article is more useful due to the limitation. A person would need to justify their own Wikipedia article before a mention of them would be made here at Geodesy.

I suggest that the rule need not be enforced for people before 1900, but it should certainly be enforced for living people. Otherwise self-promotion may distort the contents of this article. The Wikipedia:Conflict of interest guideline needs to be kept in mind. Otherwise the people themselves, or their students, will add mentions here and we won't have any idea of whether they are notable in their own right. EdJohnston (talk) 20:50, 24 January 2008 (UTC)

Strong agreement. Many such lists require that such people (or places, organizations, etc) be notable enough to have a Wikipedia article to be listed. I would also encourage the complete removal of the University institutes section. Virtually all significant large universities will have some level of coverage of geodesy. Cheers Geologyguy (talk) 21:03, 24 January 2008 (UTC)

Yep, I agree, particularly about the universities. I've been meaning to do something about that for a while. I say just remove it. Eve (talk) 21:21, 24 January 2008 (UTC)

OR Link Should be deleted

Under "External Links" there's a link to a SourceForge project called "GeographicLib" that claims to be "1000 times more accurate than Vincenty" and accurate within 15nm. I've been in this field 20 years, and that claim is just silly. No one has measured the Geoid with that kind of accuracy - no geodetic solution could be, either.

I vote to delete the link. What do others think? 204.99.19.150 (talk) 22:37, 2 March 2010 (UTC)

Implicit in this claim of accuracy is the assumption that the task is to find shortest path on a mathematically defined ellipsoid and not on the geoid or the surface of the earth. An ellipsoid is a useful approximation of the geoid (despite differing from it by up to 100m). Furthermore being able to obtain highly accurate solutions for the ellipsoid is important in some applications (e.g., in order to ensure that the triangle inequality is satisfied). Cffk (talk) 20:53, 28 July 2011 (UTC)

Cffk

User:Cffk is (presumably) promoting his own work in this this edit, which I reverted. Can someone knowledgable take a look and decide what if anything should be said in the article about this? Dicklyon (talk) 04:14, 23 February 2011 (UTC)

In my opinion this is a very specific, mathematical detail that does not need to be mentioned here. If a further discussion about reference ellipsoids is desired, there are more standard textbooks covering this topic very well, e.g. The figure of the Earth : theoretical geodesy and the Earth's interior by Moritz.

Bpshop99 (talk) 11:51, 19 May 2022 (UTC)

Geodetic observational concepts

The term "gravity vector" is used twice in this section but not defined.

I'm trying to use this as a learning resource, rather than pointing out missing content for fun.

Will someone "in the know" please add this to this section?

Planetary geodesy

With the ongoing evolution of interplanetary missions and remote sensing technologies, the field of geodesy has rightly expanded beyond our native planet. Planetary geodesy is also called simply "geodesy" within the context of studying other worlds (e.g. NASA's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) the next probe for Mars). Unfortunately, this subfield(?) lacks its own separate page or any section for expanded information. Since this is just a hobby for me, I'll defer it to the community, what's the proper inclusion of this?

Search "Planetary geodesy" "Extraterrestrial geodesy", "Geodesy of Mars" etc. From what I can tell, it's effectively covering the same metrics via other means due to the obvious differences in accessibility of the subject. Although similarities found in remote sensing from artifical satellites is a telling commonality here.

Anyway, please don't get stuck on the notion that the root of the prefix meaning "Earth" is crucial. Let's not be unduly geocentric here. I think that using simply "Geodesy" is appropriate with or without the context of a specific planet, while any necessary context would naturally precede the application of the science. JimsMaher (talk) 10:01, 14 May 2016 (UTC)

Geodetic Control Mark image

Section Point positioning includes a photographic image of a "Geodetic Control Mark". The term does not arise within the text of that section, nor indeed anywhere else in the article. So the naive reader will be left to guess why and how such a thing is relevant to "point positioning". I'm guessing that said "Geodetic Control Mark" is terminology specific to one (perhaps more) English-speaking nation, and refers to a geodetic reference point that fulfils the need described in this text from the section:

One purpose of point positioning is the provision of known points for mapping measurements, also known as (horizontal and vertical) control. In every country, thousands of such known points exist and are normally documented by the national mapping agencies.

Perhaps the image is an example of the "thousands of such known points". Could somebody versed in the practical side of surveying and mapping please do whatever it takes to tie the image to the text, explaining why and where such an item – a "Geodetic Control Mark" – is relevant to the purpose(s) of "point positioning"? Otherwise, I'd be tempted to remove the image as irrelevant to the article in its entirety – but surely it's not! yoyo (talk) 05:12, 15 January 2017 (UTC)

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Yup u already kno dis iz skraig be ht faktz. And kant nobody tell me iss kap.

You already know these things are true. And nobody will be able to say it’sa life or opinion. 2601:640:8700:1F60:2439:90E7:727D:D543 (talk) 01:16, 6 January 2022 (UTC)

Keen grasp of the obvious. - Tom Epsilon (edits) (email) 04:35, 6 February 2022 (UTC)

Section Definition should be entirely rewritten

The section "definition" does not represent the common definition of Geodesy. See for instance Physical Geodesy (2006) Hofmann-Wellenhof and Moritz or Geodesy (2012) Torge and Müller or Geodesy (2015) Vanicek and Krakiwsky. This section should be entirely rewritten. Bpshop99 (talk) 11:47, 19 May 2022 (UTC)