Future of GPS?

[Bill Perkins]

Talk of Saddam and others delivering warheads with unmanned planes as well as the proliferation of cruise missile technology makes me wonder if the publically available accurate GPS signal will come to be seen as a peacetime luxury we can no longer afford . At least at some threat level ( color? ) . Maybe the lighthouses should keep transmitting Morse Code for an RDF backup ?

[Ian G Wright]

During the last Gulf War the SA wobble was turned off to enable those troops that had bought civvie GPS's to get the full benefit.

IanW.

[Ian McColgin]

They had it downgraded for alleged national security until the last Gulf War when the military needed so many GPS units that they purchased civilian models off the shelf . . .

Degrading the GPS again is spurious security. The weapns of choise for terrorists are not improved by GPS and often do not even require that kind of accuracy.

Sometimes the phoney security measures seem analogous to phoney accuracy and deceptive precision. You see digital watches the read to the nearest 100th of a second. But they gain or lose variable amounts each day and are not set correctly in the first place. It's really the illusion of precision coupled with no pretence of accuracy.

I'm not that surpirsed when uniformed citizens are confused about what's a real threat and what's not, but the hysteria of our government is quite alarming. It means that they are quite able to posture and work quite hard on all the wrong things and miss the actual threats alltogether.

[Thaddeus J. Van Gilder]

I am curious what happens when the terrorists send a virus into our satelites and we can't use them.

No satelite TV, No GPS, No Cell phones,No beepers, None of that...

That would be cool!!!

That would make cruising this summer much better. None of the people that require electronic claptrap to survive would be out on their I'mayuppie 60's and their Momoney 45's.
Yup, It would be a quieter summer on the Chesapeake.

[Dan McCosh]

The irony to the concern over the accuracy of the U.S. GPS system is that the alternative is to lock into the Russsian satellites.

[Bill Perkins]

I feel better Ian McC knowing YOU , at least , know what's up . Maybe your pomposity will protect us All ; allies , neighbors to wackos , and troops in the field ?

[ 02-11-2003, 12:55 AM: Message edited by: Bill Perkins ]

[Nicholas Carey]

My bet is that if the balloon goes up, selective availability will be turned on again (and dialed up). There's no way that they're going to give the other guys' spotters the ability to call down accurate fire.

[Rancocas]

A few years ago I was on a caribou hunt in far northern Quebec. My guide and I were several miles away from camp, and heading back. He was using a GPS. I had my faithful old compass.
His GPS showed our course to be one way. My compass showed it to be about 45 degrees in another direction. We had a little argument, but finally the guide agreed to follow my course, just to prove I was wrong.
I was right! That made me feel pretty good! GPS - bah! I'll stick with the compass.
In truth, though, I think my French Canadian guide just didn't know how to use his GPS properly. He was a good guide, otherwise.

[Dave Hadfield]

Next time pick an Inuit guide. (But take your compass anyway!)

[cs]

I'm not sure just how accurate a civilian GPS system is. What I will tell you is from personal experiance.

A military GPS unit is called a "plugger". Now when you use a plugger in everyday use the accuracy can vary anywhere from +/-100 meters to +/-10 meters. Now if the plugger is loaded with the correct key the accuracy is within 1 meter. The civilian GPS that I have used in survey class was never that accurate.

Ian touches on a few good points, one in paticular about precision and accuracy. It is possible to be precise but still wrong. You can measure something a hundered times and get a "precise" measurement. But if the tape measure goes from 4' to 6' and leaves out 5' you are not accurate in your measurment.

Another point is that the bad guys don't depend on that level of accuracy. There weapons are more similar to a shotgun, and they take the shotgun approach. And if the hit the wrong target they don't care.

Another thing, not all our weapons depend on GPS. In fact my launcher does not depend on GPS. We do require accurate survey information, which is helped by GPS, but this can be optained by more traditional methods if needed.

Chad

[NormMessinger]

Be pessimistic and avoid dissapointment.

However, I suspect there is way too many civilian systems now connected to the GPS for it to be shut down.

[Peter Malcolm Jardine]

U.S military satellites are using a secure uplink, and are not the same satellite used for other purposes... at least I would assume that's true. The number of satellites up there in the control of the US military is classified. Who knows how much of star wars got completed, either on or off the record... As I've said before, in military technology, no one in the world is even close. GPS is good to about 25 or 30 feet. US military GPS can put a missile through a 3 foot square window. ;)

[Donn]

The GPS constellation currently consists of 27 birds, the most recent launch was just last week. The military uses the exact same GPS signals that we do.

[cs]

Donn there is no question the civilian GPS units use the same satillite as the military, but without the proper key you won't get the same accuracy.

Chad

[NormMessinger]

A couple of years ago, and earlier than expected, the military turned off what ever it was that reduced the civilian GPS units accuracy. It sure made a difference in my antique unit. Since the FAA has published non-precision approaches to some airports, is allowing some IFR flight plans based on GPS, allows the use of GPS for IFR navagation, and is working on a WAAS system to allow precision approaches.

Which is not to say there is not still differences between civilian and military but the accuracy of civilian took a big jump a while back.

[cs]

Norm do you know what the degree of error is on your old system? Our pluggers gives us a readout on what the error is.

Chad

[seafox61]

a side note likely...
on NPR this morning their was a report that the search teams looking for shuttal debrea are marking where each piece if found with gps and using the data to predict where more pieces are to be found
jeffery

[NormMessinger]

Chad, I don't know. It has been a couple of years since I paid any attention so ya can't expect me to remember. Senior moments, you know. The accuracy would have been determined by the signal degregation rather than the unit. But you know that. It seemed to me that I could have taxied right up the the hangar door even with the old accuracy but I never risked trying it. Even with the GPS in the cockpit I always used FOM for navigation.

[ 02-11-2003, 12:37 PM: Message edited by: NormMessinger ]

[Donn]

That something that was turned off was SA, Selective Availability. It was a fudging of the timing aspect of the signal. My pre-DGPS handheld went from ~20 meters to ~3 meters accuracy, checked against my LORAN. The President turned it off in 2000.

Prior to that, several people were running DGPS re-timing logarithms on web-servers, so if you could connect your GPS to your PC, you could feed in the correct timing. The hack was around for 3-4 years before SA was turned off.

[Rocky]

The Russians have a similar system, right?

Was GPS was an outgrowth of SDI?

Went out on Lake Hopatcong without punching in a waypoint, got lost with a whiner in the boat. Learned my lesson. (On a hazy summer night getting lost on a 9-mile long lake is not as hard as it sounds.)

[ 02-11-2003, 04:01 PM: Message edited by: Rocky ]

[JeffH]

Just to clear up some questions....

The civilian and military versions of GPS use the same satelites, just different code. The military code was theoretically more precise, but over time, as such things tend to happen, civilian users found ways to make their units just as accurate as the military versions, even with the SA activated. Hence, the gov't found no particular reason to keep SA on. If you're willing to cough up the bucks (about $50 grand a year for a subscription) you can get a satelite-linked differential signal good anywhere in the world, less than a meter accuracy, with or without SA. Amazing stuff.

The Russian system is GLONASS, but use with care since they use a different geological reference datum (those pesky Russians gotta be different smile.gif ). They claim about 70 meter accuracy, if memory serves. Anybody ever actually seen a GLONASS system for sale, just out of curiosity?

Chad, I'm suprised you only got 1 meter out of your survey unit. My father has a good, but still not survey-quality, unit that will get 1 CENTI-meter if left still for a few minutes.

Jeff

[Dan McCosh]

My WAAS--enabled GPS is supposed to be good to 2-3 meters absolute position. Interesting is that GPS is used as a car-test instrument, which gives relative positional accuracy of less than a foot at 60 mph or so. Industrial (not military) units promise absolute position withing a 1 cm. cube. The local-area -enabled systems are used to land aircraft without a pilot touching the controls. This is a problem if they turn the system off or reduce its accuracy.

[Donn]

The "accuracy" and "utility" of GPS is dependent on two things...the timing of the signal, and the software that interprets and reports on the signal.

GPS works on a time-at-position basis...just like LORAN. Assumptions are made, by software, in the forecast of future time/position locations.

If you don't, or can't, factor in little things like currents, tides and wind, the forecasts can go way astray.

I've fished in places where I had to hold the boat over a structure that required me to hold a 12kt speed to stand still. Imagine the variance in the assumptions that the software makes.

The primary value of GPS, for both civilian and military uses, is not position...rather position over time.

[John Bell]

I for one am glad they turned off SA. It made possible one of my other distractions: Geocaching! It's great fun to travel to the other side of the country and find a little treasure someone hid off a little trail in a pretty little park you would have never gone to on your own. At any rate it's healthier than sitting in the bar a the Holiday Inn. For a really good time, tell your kids you're going to take them on a real treasure hunt and go find one with them. They'll want to do more, trust me.

Google on "geocaching" if you want more information.

[Nicholas Carey]

Originally posted by cs:
I'm not sure just how accurate a civilian GPS system is. What I will tell you is from personal experiance.

A military GPS unit is called a "plugger". Now when you use a plugger in everyday use the accuracy can vary anywhere from +/-100 meters to +/-10 meters. Now if the plugger is loaded with the correct key the accuracy is within 1 meter. The civilian GPS that I have used in survey class was never that accurate.GPS accuracy is measured three ways: absolute, repeatable and relative. Absolute accuracy is just that: it answers the question, "Where am I?" Repeatable accuracy measures how accurately you can return to a particular fix: it answers the question, "How well can the GPS receiver take me back to the fix I made last week?". And relative accuracy measures the accuracy of 2 fixes made by identical hardware simultaneously: it answers the question, "How well does my fix measure up to your fix?"

Accuracy measurements are statistical and are expressed as a measurement at a particular confidence level.

Military GPS receivers (PPS) are accurate to +/- 20m at a 95% confidence level.

With SA on, a civilian GPS receiver (SPS) is accurate to +/-100 metres at a 95% confidence level. However, the SA degradation is dialed in, so the powers that be could up it, conceivably, to +/- 1 kilometre or so. With SA off, a civilian receiver should get the same performance as a PPS receiver.

This is, of course, a gross simplification. Just for starters, GPS accuracy varies with latitude -- the further north you go the lower the accuracy.

As for your +/- 1 m fixes on your PPS receiver, you may well get those, but not at the 95% confidence level. Your confidence level will be far lower than that.

[rodcross]

I don't care what anyone thinks about the GPS system. I think it is a marvel! Last Summer I avoided a series of sand bars off Nantucket, in pea-soup fog with that nifty little box.

When the GPS says you're close, you slow down and get careful.

Creeping about in the fog with 100meter accuracy is a modern miracle. I'm happy if I know I'm within a mile-five miles, in a pinch-of where I'm supposed to be.

When it is pitch dark, I don't need a 3 foot window. All I need is to know what I should be worried about within a few miles.

When something breaks out in the middle-east, are you going to be surprised if your GPS says you're off the coast of Ireland?

[Nicholas Carey]

That's always been my attitude when I heard people whining about the 'poor' quality of the fix you get with an SPS receiver with SA turned on (more or less +/1 100m in 3d). I wouldn't trust the charts you're using to navigate any closer than that.

[Scott Rosen]

What Rod said.

[George Roberts]

It as amazing how much good the military does for us even in peace time.

As I recall the number of digits in the display of my GPS (I lost it) provided a 70' movement before the digits would change. (25k miles changed into seconds of an arc as I recall).

70' was enough to not be able to see a campsite I was looking for from my boat.

[Meerkat]

FWIW, it was reported 2-3 weeks back that there was a shortage of civilian GPS units because the military had bought a bunch to issue to the troopies bound for Iraq. I doubt they'll turn SA off.

[Andrew Craig-Bennett]

Well,here's my only bit of military intelligence trivia.

During the Kuwait war I was in charge of several ships operating into the Arabian Gulf and since they were under the British flag I got to go to Intelligence briefings.

One gem that I recall is the reason why the Iraqi SCUD missiles were so inaccurate....

....The Russians had turned off GLONASS, for the duration.

[igatenby]

I had my height accurately measured by GPS about a decade back. 198cm. Took a few minutes to get the accuracy.

Ian

[StanDSmith]

I would think that the government has granular enough control to disable the sattelite signals while visible over US territories. There are many government and civilian uses of GPS tho, I think it would take an attack that utilized GPS before we could rationalize the 'expense' of disabling.

I have two handheld units, they are worth there weight in gold. One Magellan and one Garmin eTrek (has cartography) I hope to hook the units up to the old cruise control at some point.

Stan