Talk:Geodesy
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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)
I created 'reference ellipsoid'. Some of the stuff in this page should IMO go there.
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[edit] 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 difficulte 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)
[edit] 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)
[edit] 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)
[edit] 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)
[edit] Vandalism
My friend is adding his name to list of famous surveyors in 20th century. Can someone block page from editing by unregistered users?
[edit] 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)
[edit] 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)
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- 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)
- Here's the CodeProject version of the same C# code:
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)
[edit] 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)
