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Old 24-03-2015, 17:29   #91
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Re: How Does GPS Work?

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Originally Posted by gbgreen59 View Post
Or how about discussing WGS-84 ellipsoidal model instead for a model of the Earth's shape. Or more generally, what is the latest greatest ellipsoidal model? Normally, GPS receivers use the WGS-84 model of the ellipsoid and not a sphere.
This is a current question for me right now as I am thinking of upgrading to a GPS from my existing couple of mid to late 90s units.

My existing units allow the user to select datum from dozens or more preloaded datum corrections. So I check my paper chart and then select that datum on my GPS.

Does this feature still exist on the everyday garden variety recreational marine GPS.

I thinking perhaps that with the preponderance of electronic charts often preloaded, this feature may be obsolete.

Anyone know???
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Old 24-03-2015, 17:56   #92
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Re: How Does GPS Work?

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Thanks for the excellent write up about GPS Dave

However I strongly disagree with your last paragraph. This suggestion does not promote any advancement of knowledge to those of us who may not have significant technical understanding. It could be seen as "just dumming down" even though I dont think that is your motive.

I reckon many of us posting here or just reading do not have "significant technical understanding" otherwise the issue would not have raised. You and several others have provided us with a now greater understanding than we had last week. For some you have confirmed what we thought we knew and for others presumably you have corrected some fallacies.

FWIW, it is easier (for me anyway) to understand this subject when it is written by mariner (ie you and others on CF) then trying to google a reliable source that isn't written by say a maths professor for an advanced scientific engineering design group or whatever.

I actually agree with Dave here --

Maybe his statement was too blanket -- technical topics maybe shouldn't be completely left with the experts. But there's a deeper point there. The Internet gives everyone basically an equal platform to spout off. So a person who is utterly clueless about how GPS works may write complete nonsense, in a post of the exactly the same format as that of a real expert like Dave. This is very different from the pre-Internet days, when column-inches were rationed out only after a considered judgment about whether a given opinion is worth printing or not.

The thing is -- we should all try to be more conscious of what we don't know. Aristotle said that this is the very key to wisdom -- knowing what you don't know. Try to form a judgement about who knows more -- and listen. Maybe critically -- but at least listen. And when we know very little -- be a little more modest. Resist the temptation to spout off that something seems to be somehow when we haven't even taken the time to read anything on the matter, and we're actually clueless, to be frank. I realize that I'm one of the bigger sinners in this regard -- but the lesson is no less valid ("do as I say, not as I do . . ." ).
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Old 24-03-2015, 20:28   #93
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Re: How Does GPS Work?

I think we should not try to "censor" anybody unless they are doing something "cruel or dangerous" to others. I think 99% of readers can tell when they are reading a bunch of nonsense.
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Old 24-03-2015, 20:35   #94
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Re: How Does GPS Work?

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Originally Posted by Wotname View Post
My existing units allow the user to select datum from dozens or more preloaded datum corrections. So I check my paper chart and then select that datum on my GPS.

Does this feature still exist on the everyday garden variety recreational marine GPS.
It does, at least on Garmin chartplotters.
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Old 25-03-2015, 05:14   #95
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Re: How Does GPS Work?

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I think we should not try to "censor" anybody unless they are doing something "cruel or dangerous" to others. I think 99% of readers can tell when they are reading a bunch of nonsense.
Of course. I think everyone agrees about that.
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Old 25-03-2015, 10:23   #96
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Re: How Does GPS Work?

I wasn't being elitist. But In several technical threads, its clear there are experts. Yet often people persist in trying to argue the science often quoting sources they don't understand or they parrots understood half truths.

I mean if you know only something , surely the first thing you do is ask
Questions not advance theories.

All it does is extend the thread noise threshold


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Old 25-03-2015, 11:41   #97
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Re: How Does GPS Work?

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I didn't read all of the posts in this thread. I'm just responding to the title. I really don't have any credentials built in this community, so I understand why people may not accept what I say as creditable information. Anyway, I'll dive in :
Me neither... I didn't read all the posts & I run the risk of repeating something that was already said but "c'est la vie!" here it is: I learned, only recently, that, had it not been for Albert "E=mc2" & his theory of relativity, we wouldn't have GPS or accurate GPS ! The reason is simple: Time in the satellites runs slower than on earth because they travel at a faster speed than we do at the surface of the earth, therefore their time runs more slowly than ours & time is critical in calculating our distances from the different satellites to our car (or to my paraglider) GPS...

"The Global Positioning System (GPS) is a constellation of about 24 artificial satellites. The GPS satellites are uniformly distributed in a total of six orbits such that there are four satellites per orbit. This number of satellites and spatial distribution of orbits insures that at least eight satellites can be simultaneously seen at any time from almost anywhere on Earth. The GPS satellites circle the Earth at an altitude of about 20,000 km (13,000 miles) and complete two full orbits every day. The GPS satellites are not in ageostationary orbit, but rise and set two times per day. Each satellite broadcasts radio waves towards Earth that contain information regarding its position and time. We can receive this information by using special receivers, called GPS receivers, which can detect and decode this information. By combining signals transmitted by several satellites and received simultaneously, a GPS receiver can calculate its position on the Earth (i.e., its latitude and longitude) with an accuracy of approximately 10 m. There are more sophisticated receivers that can be used to determine position with an accuracy of a few millimeters."
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Old 25-03-2015, 11:57   #98
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Re: How Does GPS Work?

we should also thank luminaries like Lorentz, Poincaré, and some others too. many people contributed to special relativity
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Old 25-03-2015, 12:02   #99
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Re: How Does GPS Work?

Lorentz especially gets little credit these days. Einstein wasn't the only "Einstein" of his time.
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Old 25-03-2015, 12:06   #100
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Re: How Does GPS Work?

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Originally Posted by transmitterdan View Post
Lorentz especially gets little credit these days. Einstein wasn't the only "Einstein" of his time.
indeed , he was arguably greater
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Old 25-03-2015, 12:15   #101
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Re: How Does GPS Work?

Wow 5 pages to answer the question "how does a GPS work". Seems some people have a much more complex GPS than I do.

My GPS works when I turn it on. I don't really feel the need to know more than that
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Old 25-03-2015, 12:52   #102
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Re: How Does GPS Work?

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Wow 5 pages to answer the question "how does a GPS work". Seems some people have a much more complex GPS than I do.

My GPS works when I turn it on. I don't really feel the need to know more than that

Agreed, you may continue to use a device invented by people , far far smarter then you.
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Old 25-03-2015, 13:16   #103
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Re: How Does GPS Work?

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Originally Posted by Sailor Doug View Post
Dan the reason why I ask for manufactures sites is they always try to sell the best technologies. Most of the papers posted on this site refer thesis by phd candidates and are very smart girls and guys. They are giving a lot of proposed new free information away to advance their carers. They are promoting new future technology but not repeating current methods. Companies that know how their systems work are protective of proprietary information.
Doppler shift is a pretty old piece of science. Speed differential without know position is not possible. A triangulation of position of position change is required with Doppler shift assisting in getting accurate timed based position change. (speed)
Atonomas navigation is being advance using multiple antennas, assistance corrections and solid state gyros.
Our conversation needs to be about how consumer marine gps works. Look at the array of antennas and vision sensors on atonamas vehicles we don't have this on our boats.
Our gps gives very accurate speed but a bit of latency is a problems for some of us, and some calculated date also suffers from fractal distortion.



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Correct Sailor Doug.The GARMIN link I put up a couple of days ago explained clearly how all calculations result from establishing the position of the GPS receiver. I guess this is why it's called a GPS
Not sure why this thread is still going.
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how long has this been going on and why wasn't I told about it earlier.....
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Old 25-03-2015, 13:22   #104
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Re: How Does GPS Work?

[QUOTE=ALAIN97133;1784367]Me neither... I didn't read all the posts & I run the risk of repeating something that was already said but "c'est la vie!" here it is: I learned, only recently, that, had it not been for Albert "E=mc2" & his theory of relativity, we wouldn't have GPS or accurate GPS ! The reason is simple: Time in the satellites runs slower than on earth because they travel at a faster speed than we do at the surface of the earth, therefore their time runs more slowly than ours & time is critical in calculating our distances from the different satellites to our car (or to my paraglider) GPS...

"The Global Positioning System (GPS) is a constellation of about 24 artificial satellites. The GPS satellites are uniformly distributed in a total of six orbits such that there are four satellites per orbit. This number of satellites and spatial distribution of orbits insures that at least eight satellites can be simultaneously seen at any time from almost anywhere on Earth. The GPS satellites circle the Earth at an altitude of about 20,000 km (13,000 miles) and complete two full orbits every day. The GPS satellites are not in ageostationary orbit, but rise and set two times per day. Each satellite broadcasts radio waves towards Earth that contain information regarding its position and time. We can receive this information by using special receivers, called GPS receivers, which can detect and decode this information. By combining signals transmitted by several satellites and received simultaneously, a GPS receiver can calculate its position on the Earth (i.e., its latitude and longitude) with an accuracy of approximately 10 m. There are more sophisticated receivers that can be used to determine position with an accuracy of a few millimeters."[/QUOTE
Yup. You got it. Correct
".......By combining signals transmitted by several satellites and received simultaneously, a GPS receiver can calculate its position on the Earth (i.e., its latitude and longitude) with an accuracy of approximately 10 m....."
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how long has this been going on and why wasn't I told about it earlier.....
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Old 25-03-2015, 13:24   #105
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Re: How Does GPS Work?

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Correct Sailor Doug.The GARMIN link I put up a couple of days ago explained clearly how all calculations result from establishing the position of the GPS receiver. I guess this is why it's called a GPS
Not sure why this thread is still going.
without betraying commercial confidences,. I can tell you, you are categorically wrong about Garmin.

The process has been explained to you by several posters. If you continue to ignore the truth and simply peddle your "intuitive" undertasnding, Im sorry, for as Sherlock Holmes said, everyone can " see", few can " observe ". or as some have put it, " theres none so blind as those that will not see "

bye bye
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