What is the most accurate GPS in the World?

Keith Lane

Keith Lane

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Keith Lane
Well, I just had one of those phone calls from the boss.
Him: What does WAAS mean, what does it do?"
Me: Read to him directly from Garmin's website http://www8.garmin.com/aboutGPS/waas.html including the accuracy of each system (see text near the bottom of web page. You never,ever tell him anything you cannot back up with evidence gathered from somewhere.
Him: "I know there is a GPS that will go down to sub-millimeter accuracy."
Me: "I don't think so. The best surveying GPS I have ever seen/considered/shopped for was 3mm horizontal/5mm vertical."

Him:"G##%^R$%$^, I know there is a sub-millimeter system!!!!"
(Hangs up phone)
Me: (to dead phone) "If you already know more than me, why did you call?"

So............
Does anybody here know of a sub-millimeter accurate GPS, that is available to civilians?
 
Well technically you and he mean GPS receiver, as there really is only one system.

I doubt the limitations of reciever architecture would allow for sub-mm accuracy, never mind the system.
 
I am impressed by the ones the surveyors use...
3mm horizontal/5mm vertical
Click to expand...
WOW...

What does he want to do with it pray tell????
 
I was at the LIGO observatory in Richland WA and asked the scientists how they got that kind of accuracy out of GPS.

The answer was basically, you can get almost any precision you want if you wait long enough. There is a practical limit as each digit of precision takes much longer than the previous.

Joe
 
Kelvin said:
I am impressed by the ones the surveyors use...

WOW...

What does he want to do with it pray tell????
Click to expand...

He probably told somebody he knew of one, and now wants to be able to confirm. Mouth in gear first, get facts later.
 
Areeda said:
I was at the LIGO observatory in Richland WA and asked the scientists how they got that kind of accuracy out of GPS.

The answer was basically, you can get almost any precision you want if you wait long enough. There is a practical limit as each digit of precision takes much longer than the previous.

Joe
Click to expand...

It does seem plausible to achieve sub CENTIMETER accuracy if you average enough readings although at some point you'll be relying on orbital positions that aren't known well enough to do any better no matter how long a period you measure over. But I'd have to say that sub MILLIMETER just ain't gonna happen with GPS as we know it today no matter how long you acquire the positions. Even if the orbits were accurate enough, given the geometry and wavelengths involved I just don't see how this could be feasible. Heck, I'll bet there's an uncompensated error just from the thermal expansion of the space vehicle's antenna that would exceed a substantial fraction of a millimeter. And where on your measuring antenna would you pick as the center of the measurement to less than a mm?
 
Since ti seems that no one is actually reading the links I posted here is a little nugget

The Benchmark Survey System replaces legacy NGA conventional survey techniques with a GPS-only system, maintaining sub-millimeter positioning accuracy while increasing throughput by 400 percent, with an 85 percent decrease in manpower. Results agree with recent NGA precise survey data to better than 0.6 mm horizontal and better than 1.0 mm vertical.
Click to expand...

ARL:UT has developed and deployed the entire system; it includes commercial hardware components such as the GPS receiver and antenna, custom-designed mounting hardware specific to the HHSTT, and custom data processing software consisting of both a graphical interface and a GPS network position estimation application. In this article, we compare BSS results with a recent NGA survey, showing that the BSS has achieved the accuracy and throughput goals in the requirements.
Operating Principles. BSS hardware consists of 25 self-contained GPS data collection and storage units, or survey nodes, deployed together so that GPS observations are recorded concurrendy at 25 benchmarks along the HHSTT. Each survey node consists of a ruggedized electronics enclosure containing a GPS receiver, a single-board computer, a rechargeable battery pack and supporting electronics, plus a GPS antenna with a mechanical mount that supports the antenna and provides precise control of its location relative to the survey benchmark.
Click to expand...



So it is possible and has been demonstrated.
 
smigaldi said:
Since ti seems that no one is actually reading the links I posted here is a little nugget.
Click to expand...

Yup, I read it. But it is a one-off system that it there only to verify the position of the rails on the highest speed land vehicle in history. That Ain't no ordinary railroad, and sure ain't no ordinary GPS. It is, as you say a sub-millimeter GPS. It just sits there and gathers a gazillion samples on the same location.
I could give the boss all the time and bandwidth in the world and he would not find that. He seems to think (or knows, in his mind) there is an end-user system out there that will do what he claims. I say it just ain't so.
Oddly enough I was approached earlier this year about testing those very rails to verify their stress free (neutral) temperature. I am the North American tech support guy for the only non-destructive SFT testing system in use today.
 
Keith Lane said:
Yup, I read it. But it is a one-off system that it there only to verify the position of the rails on the highest speed land vehicle in history. That Ain't no ordinary railroad, and sure ain't no ordinary GPS. It is, as you say a sub-millimeter GPS. It just sits there and gathers a gazillion samples on the same location.
I could give the boss all the time and bandwidth in the world and he would not find that. He seems to think (or knows, in his mind) there is an end-user system out there that will do what he claims. I say it just ain't so.
Oddly enough I was approached earlier this year about testing those very rails to verify their stress free (neutral) temperature. I am the North American tech support guy for the only non-destructive SFT testing system in use today.
Click to expand...

Maybe not an end-user system, but it's hardly one-off. Google "GPS plate tectonics"; "GPS plate slippage" and similar terms. These systems account for the refraction of the GPS signal entering the atmosphere from space and other various corrections. Geologists make these types of measurements. Likely back issues of GPS world has information too- this can be googled as well.
 
Kelvin said:
I am impressed by the ones the surveyors use...
Click to expand...

Surveyor ones aren't that impressive as the ones I'm familiar with use surveyed point base station differential GPS. Developed back when SA was still turned on. GPS in general is very precise in the local region, but not very accurate when SA was turned on. But it could tell you how far apart two receivers were in a local area.

So you put the base station on top of the surveyor's reference point, and walk around with a remote receiver. The base station would broadcast differential data to the remote, or both would log for post processing, and you could get very very good position data WRT the reference point. That was back in the mid-to-late-90's.

I haven't done market surveys recently on current high-accuracy consumer stuff, so I may be a bit out of date.

Edit: WAAS is essentially the surveyed base station concept, but applied to a wider area, so the accuracy is better, but not as good as local area base.

--Carlos V.
 
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smigaldi said:
Since ti seems that no one is actually reading the links I posted here is a little nugget







So it is possible and has been demonstrated.
Click to expand...


Just for clarifacation a Millimeter is .03937 of an inch. .6 MM is .02362 in. That is about the thickness of a cover on a pack of matches. Measurements that close are next to impossible to prove or disprove and they know it...
 
smigaldi said:
Since ti seems that no one is actually reading the links I posted here is a little nugget

So it is possible and has been demonstrated.
Click to expand...

That system claims to provide sub-millimeter relative accuracy (and I'd only accept that claim if it was confirmed with inferometry). I thought we were talking about absolute accuracy, i.e. accurately determining a position on the earth's surface as in the lat/lon.
 
Unbeliever said:
Surveyor ones aren't that impressive as the ones I'm familiar with use surveyed point base station differential GPS. Developed back when SA was still turned on. GPS in general is very precise in the local region, but not very accurate when SA was turned on. But it could tell you how far apart two receivers were in a local area.

So you put the base station on top of the surveyor's reference point, and walk around with a remote receiver. The base station would broadcast differential data to the remote, or both would log for post processing, and you could get very very good position data WRT the reference point. That was back in the mid-to-late-90's.

I haven't done market surveys recently on current high-accuracy consumer stuff, so I may be a bit out of date.

Edit: WAAS is essentially the surveyed base station concept, but applied to a wider area, so the accuracy is better, but not as good as local area base.

--Carlos V.
Click to expand...
That system sounds more like LAAS than WAAS.
 
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