Talk:Global Positioning System/Archive 8: Difference between revisions

Revision as of 00:02, 14 August 2015

Revision as of 00:04, 27 August 2015

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*''Before'' anyone adds anything to the article be forewarned that if it is not agreed upon here (by which I mean if there is no consensus to move forward with the idea) and/or the change results in another round of reverting the article will be placed back on lockdown and the time for which you will all be unable to edit it will be extended. Therefore, it would be in everyone's best interest to discuss this to death to make certain that whatever you are going to do to the article is done with the majority consensus and that the disagreeing minority does not start or cause to be continued an edit or revert war. [[User:TomStar81|TomStar81]] ([[User talk:TomStar81|Talk]]) 17:57, 6 July 2015 (UTC)

{{reflist-talk}}

=="Main article: GNSS positioning calculation" should be removed==

"Main article: GNSS positioning calculation" at the beginning of the Navigation section should be removed. Saying "GNSS positioning calculation" is the main article for GPS is like saying the United Nations is the main government for the United States of America. There appears to be no justification whatsoever for calling "GNSS positioning calculation" the main article. GPS is an American developed system. The GPS article Navigation section was written without any reliance on "GNSS positioning calculation". "GNSS positioning calculation" is not very clearly written. It uses very terse notation which is more likely to confuse the reader rather than to enlighten him or her. [[User:RHB100|RHB100]] ([[User talk:RHB100|talk]]) 18:43, 15 July 2015 (UTC)

:I've changed it to a "Further" as I think you're right that "Main" is inappropriate. [[User:Kendall-K1|Kendall-K1]] ([[User talk:Kendall-K1|talk]]) 21:14, 15 July 2015 (UTC)

Alright, thank you [[User:Kendall-K1|Kendall-K1]]. [[User:RHB100|RHB100]] ([[User talk:RHB100|talk]]) 21:27, 15 July 2015 (UTC)

Is there any need for the proposed merger message, "It has been suggested that this section be merged into GNSS positioning calculation. (Discuss) Proposed since April 2015" near the beginning of the Navigation section. There has been no expression of support for this at the link provided. GPS is an American system. This proposal should be removed. [[User:RHB100|RHB100]] ([[User talk:RHB100|talk]]) 01:33, 17 July 2015 (UTC)

:I suggest you discuss this at [[Talk:GNSS positioning calculation]] as the template says. I don't understand what "GPS is an American system" has to do with the merge proposal. [[User:Kendall-K1|Kendall-K1]] ([[User talk:Kendall-K1|talk]]) 14:28, 17 July 2015 (UTC)

I have discussed it at [[Talk:GNSS positioning calculation]]. But since the template suggests merging the two articles, it is appropriate to discuss here on the talk page for GPS in addition to the other talk page. The fact that GPS is an American developed system is important because merging the two articles would have the effect of suppressing the fact that GPS was developed by the government of the United States of America funded by American taxpayers. [[User:RHB100|RHB100]] ([[User talk:RHB100|talk]]) 20:02, 17 July 2015 (UTC)

== Trying To Track A Deletion: Pre-launch clock adjustment calculation ==

As I remember this GPS page used to have a section on how the satellite clocks were adjusted so as to run at the same rate as the earthbound clocks. Part of it went something like:

1) GPS used the velocity of the satellite clocks with respect to the ECI frame to determine how much each satellite clock has slowed relative to a (virtual) clock at rest in the ECI frame.

2) GPS used the velocity of the earthbound clocks with respect to the ECI frame to determine how much each earthbound clock has slowed relative to a (virtual) clock at rest in the ECI frame.

3) GPS used the results of 1) & 2) to compute the expected difference in satellite clocks rates vs the earthbound clock rates due to velocity.

And equations were included. Anyway, I don't see that section anymore. I'd like to see the "old" description in that section. Can you help? - as in providing the approximate date of the deletion and/or who made the deletion or anything that would help locate the deletion. Also, I'd be interested in the "Why?" in a few words and anything else you think might be relevant.

Thanks![[User:HarvPhys|HarvPhys]] ([[User talk:HarvPhys|talk]]) 22:28, 20 July 2015 (UTC)

When did you last see the section and what was it called? [[User:RHB100|RHB100]] ([[User talk:RHB100|talk]]) 01:07, 21 July 2015 (UTC)

Have you looked at the article, {{Main|Error analysis for the Global Positioning System}}? [[User:RHB100|RHB100]] ([[User talk:RHB100|talk]]) 01:16, 21 July 2015 (UTC)

RHB, Thanks very much for your suggestion. I had not looked at the referenced article and, in fact, was unaware of its existence. I reviewed the article. I found a section that covered the topic I was interested in and was asking about. Note that it was NOT a case of a section being moved from the GPS article to this article.

In the section entitled, “Calculation of time dilation”, it discusses computing the special relativistic velocity effect of the satellite clocks versus the (theoretical) clock rate of a NON-ROTATING clock at rest at the center of the earth. That part I remember, but instead of using the approximation, I remembered the main article as using the full equation. However, this article then did NOT describe what I referred to as steps 2 & 3 (i.e., It does NOT then do a similar calculation for the special relativistic velocity effect on the GPS ROTATING ground based clocks versus the (theoretical) clock rate of a clock at rest at the center of the earth and, hence, does NOT then use the result of those two calculation of the two clocks with different rotation rates to determine the net special relativistic velocity effect of the satellite clocks versus the rotating earth bound clocks on the surface of the earth.)

I then re-read the section to see if steps 2 & 3 were covered implicitly. I focused on this section in the article:

“Note that this speed of 3874 m/s is measured relative to Earth's center rather than its surface where the GPS receivers (and users) are. This is because Earth's equipotential makes net time dilation equal across its geodesic surface.[19] That is, the combination of Special and General effects make the net time dilation at the equator equal to that of the poles, which in turn are at rest relative to the center. Hence we use the center as a reference point to represent the entire surface.”

Well, after reading it twice and thinking about it, I noted that the article has said the satellite clock adjustment has two components, one for the velocity effect and one for the difference in gravitational potential effect. The above paragraph notes that the net adjustment for all points on the surface of the earth is the same and that for two of those points, the poles of the axis of rotation, there is no rotation so the net velocity effect is the same as for the non-rotating center and, hence, the calculation used to compute the velocity effect vs a clock at rest at the center of the earth would also apply to clocks at the two poles. Hence, by IMPLICATION, the reader should figure out that for all other points on the earth, the physics would require the difference between the rotating satellite effect and the rotating earth bound clock effect and by further IMPLICATION that would mean doing steps 2 & 3 which were never explicitly mentioned.

So I guess one could say that the article implies that steps 2 & 3 are needed to understand the physics for all clocks on earth except for those at the poles. However, for me, who knew the effect and was looking for it, it took quite a bit to see that it was there by implication.

Further, when the article discussed the gravitational potential effect, a single calculation was made based on the “earth’s radius”. So I think some of the physics gets lost especially for a GPS naïve reader.

Two other points: 1) Personally, I do NOT think of this pre-launch satellite clock adjustment procedure as part of “Error Analysis”, but rather as an integral part of the basic GPS design and 2) I always thought the main purpose of Time Dilation adjustment was to sync the satellite clocks with the GPS earthbound clocks and not so much as syncing them with what the article specifies as “GPS receivers (and users)” and I must confess that if I’m wrong on that point, I have a fundamental misunderstanding, so please let me know. ( For GPS receivers’ clocks, their velocity and gravitational potential can vary especially for those used in planes and in many cases rather than tending to cancel the two effects can be additive for receiver clocks.)

Sorry if the above seems picky as I know that when you, the authors, know a topic really well, it can be difficult to see it from the reader’s perspective. Hopefully, a reader’s perspective can be helpful.

While the cited section deals in implications, it does help me a lot! However, if the original section on this topic from the GPS article can be found, I’m still interested. The best I can do is say I thought it was there in 2014 and if not, definitely in 2013. It was in the main GPS article, but I don’t remember what the section was called – maybe “Synchronization” would have been in the title, or, looking at the current index, it could have been something more general like “More Detailed Description”. Before my original post, I had scanned History to no avail.

If anyone has additional comments, they’re appreciated . However, don’t spend an inordinate amount of time as the above has indeed helped a lot.

Thanks [[Special:Contributions/32.212.188.124|32.212.188.124]] ([[User talk:32.212.188.124|talk]]) 19:25, 22 July 2015 (UTC)