Talk:Global Positioning System/Archive 7

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Links to commercial site

For the time being I have removed two links to a commercial site per wp:ELNO #5. I'm not sure whether saying to exeptionally disagree because the sources are excellent readings to make probably too long already a list of external links even longer by adding two links on a commercial site — even if the articles are really excellent. I think that by allowing this, we risk getting flooded with more manufacturers with websites having more technical articles. DVdm (talk) 13:40, 10 January 2011 (UTC)

I understand your concern. I am aware that the list of external links is already quite long, and in this regard have carefully considered the appropriateness of the links. My conclusion was that the benefits outweigh the concern about a commercial offering for the following reasons: The compendium document succeeds in providing an excellent introduction and overview of the technical concepts, an aspect in which the current article is a disgrace. Several of the current external links discuss very specific technical issues, and none of them provide a good overview or historical introduction. Finally, I think that wp:ELNO #5 does not exactly apply - obviously, any company has financial interests. However, the linked documents hardly contain any explicit advertisements or promotion. The document presenting the origins of GPS contains nothing additional but the copyright of the company. Of course I respect the opinion of others, so let's see what consensus we can get. Nageh (talk) 14:04, 10 January 2011 (UTC)

Good idea. I personally think that thay are good sources and so do you, but in the end, who are we to decide? :-) Cheers - DVdm (talk) 14:19, 10 January 2011 (UTC)

General Relativity

re: "In 1956 Friedwardt Winterberg proposed a test of general relativity using accurate atomic clocks placed in orbit in artificial satellites. To achieve accuracy requirements, GPS uses principles of general relativity to correct the satellites' atomic clocks."

Wouldn't be better to move this from "History" to the section "Error sources and analysis", along with a short discussion describing the use of general relativity to correct the atomic clocks? Psalm 119:105 (talk) 17:54, 16 January 2011 (UTC)

Maybe. I am not really happy with the current layout of the article anyway. I think it should start with an introductory (1) Principles of satellite navigation, where the basic concepts are described, then go on with (2) Development of the GPS, which discusses both historical development and more advanced concepts (including the influence of time drifting due to relativistic effects, which is significant for GPS applications, btw), then describe (3) System structure and (4) Applications, next (5) Technical specifications, and finally (6) Accuracy enhancement techniques (and (7) Other systems), leaving Navigation equations as an advanced topic in a separate article (with basics described in sections 1 and 2). Something like this. Nageh (talk) 18:58, 16 January 2011 (UTC)

Now why would anyone want to put in something as uninteresting as technical specifications yet leave out the most interesting part of the entire document, Navigation Equations. The mathematics used in the navigation equations is certainly not advanced. It is very basic and fundamental. The physics is very basic and fundamental. We certainly don't need to dumb down the article to such an extent that everything that in any way resembles mathematics or physics goes into an advanced section. RHB100 (talk) 20:30, 18 January 2011 (UTC)

This is nowhere near what I intended. Sorry, my bad. I was somehow assuming that Methods of solution of navigation equations would discuss advanced techniques, similar to section Accuracy enhancement and surveying, without taking a second look. I agree that these are basics that need to be described in the article. If not right in section (1), which was my actual intention, of the structure I proposed, then in a separate section (where best?). Still, advanced calculations are possible pertaining to accuracy enhancement techniques; they are certainly best discussed in separate articles (e.g., the GPS augmentation articles). Regarding technical specification, as a mathematician you may find them uninteresting yet they are an important aspect. I moved them pretty much to the end in my list, anyway. Hope that clarifies things. (Btw, I'm surprised you suspected me to dumb down articles. I have recently argued from the opposite position on the Scientific guidelines talk page.) Nageh (talk) 21:14, 18 January 2011 (UTC)

With regard to specifications, I think the opening paragraph describing the capabilities of GPS covers a good part these speicifications. Most of the remaining part can best be covered in an error analysis. Incorporating ""Error analysis for the Global Positioning System"" into the GPS main article would complete the technical specifications and at the same time make the article more interesting. RHB100 (talk) 19:38, 19 January 2011 (UTC)

The "error analysis" material was in this article (see this version). In October, the extensive discussion of relativistic effects was removed from this article and is now in Error analysis for the Global Positioning System. Its relevance isn't limited to error analysis, though. This article should include at least a summary of the applicability of relativity to GPS: that the satellites orbit so high and move so fast that relativistic effects are unusually large; that the system accuracy depends on precision timing to the microsecond level, so the tolerance for error is unusually small; and that, as a result of these factors, GPS system design must -- and does -- take account of relativity. We could mention that there are some smaller relativistic effects (velocity and elevation of receiving stations, for example) that aren't large enough to worry about, and refer the reader to Error analysis for the Global Positioning System for further detail on that subject. I agree with Psalm 119:105 that such a section could also include the 1956 proposal and the actual test that was conducted.

Many aspects of the treatment of relativity were discussed in great detail over the summer in this thread and the next few after it in the archive. JamesMLane t c 01:17, 21 January 2011 (UTC)

The article, Error analysis for the Global Positioning System, contains material which is even more important for GPS than the material on relativity. For example the material on the calculation and derivation of geometric dilution of precision (GDOP) is also contained in this article. I think the contents of the article, Error analysis for the Global Positioning System, should again be made a part of the GPS article. RHB100 (talk) 19:53, 21 April 2011 (UTC)

Satellite positioning inconsistency in figure

The "visual example of the GPS constellation in motion" figure seems to be inconsistent with the article. The article states "the angular difference between satellites in each orbit is 30, 105, 120, and 105 degrees" but the angular difference in the figure is 90 degrees for all satellites.

This inconsistency should be resolved one way or the other. I have also added an equivalent note to the discussion page for the figure. 134.134.139.74 (talk) 19:50, 17 February 2011 (UTC)

I don't know how you are able to determine that "the angular difference in the figure is 90 degrees for all satellites". First of all the figure provides a two dimensional depiction of three dimensional motion. It is hard to measure angles accurately in this situation. Second the satellites are continually moving. There are not only difficulties in measuring the angles between moving objects in a given plane but also the distraction of the motion in other planes. But you may have found a way to measure the angles in the figure. If so, I would like to see an explanation of how you do it. RHB100 (talk) 20:21, 22 April 2011 (UTC)

Doppler shift discovered with Sputnik? I don't think so.

As of 4/5/2011 the article reads:

A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. **They discovered that,** because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that because they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion (see Transit (satellite)).

The phrase "They discovered that," is completely out of place. These scientists did not have to receive Sputnik to "discover" Doppler shift of radio signals. Doppler is taught in applied math 101. If no Doppler shift had been observed, then *that* would have been a significant discovery.  ;-)

Therefore, please, someone, move this phrase alone to the next sentence. I suggest: "A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. Because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. Because they knew their exact location on the globe, they discovered that they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion (see Transit (satellite))."

-Al Roxburgh —Preceding unsigned comment added by 98.174.141.194 (talk) 21:48, 5 April 2011 (UTC)