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GPS Accuracy Could Start Dropping In 2010
adamengst writes "A US Government Accountability Office report raises concerns about the Air Force's ability to modernize and maintain the constellation of satellites necessary to provide GPS services to military and civilian users. TidBITS looks at the situation and possible solutions."
There he is! No, wait...
Sounds like a software/project management issue to me. I didn't finish reading the article, but I hope one of their proposed solutions was to fire the incompetent people who can't deliver on-time or within budget.
.02c
just my
Censorship is obscene. Patriotism is bigotry. Faith is a vice. Slashdot 2.0 sucks.
Best not to rely entirely on one system anyway.
http://michaelsmith.id.au
The real concern is a major solar event - if they're having a big issue replacing one every other year, imagine if a major solar storm took out a dozen at once.
Have you been touched by his noodly appendage?
Ah, and you all laughed when Europe started to launch Galileo sats. Haha!
with land disputes. "Your fence is on my property" etc. We have had problems as it is with surveys in the last couple of years. It was blamed on poorly trained surveyors and some instances issues were settled in court particularly over contradicting reports and who pays for the cost of the surveys. In one instance 1/4 mile of new fence had to be moved at a cost of $10,000 and lawyer/surveyor fees of $25,000 over the fence been 5 feet out. The land in question later was sold for $60,000. What a waste of money over a silly pissing contest.
That's OK. By then Russian GLONASS will be fully operational and both the Europeans and the Chinese are thinking of launching their own satellite navigation systems. Out of these three, chances are at least one will be available for the US to use in case of a global conflict.
Plenty of people anticipated this, but nobody has given a shit enough about it to do anything substantial. I was first hearing warnings about this years ago. As a programmer, I anticipated the Millenium Bug almost 20 years beforehand, and refused to take those shortcuts that everyone else thought were wise. Back on the GPS Ranch, meanwhile, the EU is busy putting its own superior system in place, in part because they don't want to be dependent upon our system, esp. if and when we fuck up and fail to keep it operational.
Just one more reason to move to Europe.
This isn't news. The article simply says that there have been problems getting new satellites in orbit; but the ones that are there are functioning fine. Yes, they COULD fail, but they haven't done so yet, and there isn't yet any indication that they will.
Move along, move along.
You see, you all laughed at my iPhones inability to guide me safely through the streets.
It just goes to show that my iPhone is so advanced you guys are not going to catch up with my tech until 2010!
EAT THAT SUCKERS
If you have a ground-based transmitter reference, gps can be accurate to within centimeters in 3D space.
When you think about it, GPS is a pretty cool "service" that the US government supplies for free to the world. Obviously tom toms, garmins, etc, cost money but the service itself is free (And NO I am not trying to start a political flame war here, i just think GPS is cool)
People pay for satellite radio. If we were not all so accustomed to free GPS, I wonder how many of us would pay a monthly fee for it.
Personally, I don't use GPS enough to even pay $1 a month for it. But I might not mind paying an extra sales tax when I buy a GPS enabled device - something that goes to maintaining the satellites.
a job for the Dharma Initiative...
We should be fine as long as we dont let Daniel Jackson Get ahold of them
They defend "freedom."
I'm all for opening up completely the books of any government subcontractor. If you don't like transparency, then don't take government contracts. It may be tough to police, with companies trying to cheat with subsidiaries, but I think the payoff would be enormous.
On 9/10/2001, Rumsfeld gave a speech about wasteful military spending. Check it out in print, or a small piece on CBS. There was a link to his whole speech years ago - I don't know where that went. In it he states that up to 2.3 trillion dollars is "unaccounted" for, whatever that means. If you read between the lines, he is pushing for privatization of the military. We all know how well that worked out.
Every nerds favorite hobby could be in jeopardy!
The musings of just another geek and his junk.
Best not to rely entirely on one system anyway.
Okay, so I'll just use that other GPS system.
Oh, wait a second...
Fact: Everything I say is fiction.
"What about Goecaching!?"
Every nerds favorite hobby could be in jeopardy!
"Everyone" is subjective, "hobby" is misleading and "favorite" is relative... very relative. ;)
Fact: Everything I say is fiction.
GPS Accuracy Could Start Dropping In 2010
A friends mom escaped the wreck of a 90ft Fish Packer as it hit the rocks at night in a passage with strong currents due to a problem caused by relying on GPS. It was due to something like how it derived the heading vs the direction of travel or some-such.
Moral of the story was that using static ground stations like LORAN, this would not have occurred. Anyhow, now ground stations have been dismantled and vessel's receivers scrapped and there is nothing groundbased to replace GPS with should GPS fail. High altitude communications aircraft seem viable; however, there again is a reliance on something that is not physically bolted down and easily fixable.
An interesting footnote is mentioned by Buckminster Fuller in his 50 year summation masterwork "Critical Path": on pages 186-7. The Americans started their radio-accurate mapping from Compass Island in Penobscot Bay in Maine, and proceeded by radio triangulation to work their way down to South America, across the Atlantic and up Africa to Europe. This was needed for accurately guiding bombers above the clouds, as the ground survey maps were often 10's of miles incorrect.
The Germans had done this as well for Europe and perhaps Russia, so when Berlin fell, the Russians went in early and took the German mapping data. Russia had radio-accurate maps of all of Europe and published data from the US, while the US did not have maps of Russia. This lead to the importance in the cold war of US spy planes and satellites for basic mapping for targeting ICBM's, including as suggested by Fuller a US presence in Iran and Afghanistan as radio triangulation bases. Russia performed massive deceptions of fake cities and so on to perpetuate this information gradient.
Are the 3 different GPS systems being proposed (U.S., Galileo, a possibly Russian system) be broadcasting on frequencies close enough to each other that receivers that use all 3 systems will be common and fit into cell phones?
That would be the best outcome : software defined receivers that can pick up a signal from any satellite positioning signal in the sky : GPS, wide area differential GPS, Galileo, everything. Massive redundancy would mean that if you were to go between buildings or even inside buildings, there would be a greater chance that at least some of the satellites were still visible.
Everything that depends on global positioning would work better : from airline navigation systems to X prize landers.
A normal event, sure. But a repeat of the 1859 solar flare would likely damage many satellites not in the Earth's shadow at the height of the impact. Is the whole GPS constellation set up to handle that type of event? Or would more than half the satellites go down in a hour?
Have you been touched by his noodly appendage?
WAAS is the limiting factor in most units and most cases (near urban areas) so this is a non-story. Besides, the people going for those kind of caches are experienced at reading environmental clues anyways, so not much effect there either.
Politicus
Some people in aviation are using a combination of the two. They locally transmit an offset to GPS, based on the known position of a fixed GPS reciever.
http://michaelsmith.id.au
A friends mom escaped the wreck of a 90ft Fish Packer as it hit the rocks at night in a passage with strong currents due to a problem caused by relying on GPS. It was due to something like how it derived the heading vs the direction of travel or some-such.
Something wrong there. Both LORAN and GPS only give position (GPS gives time too, but that doesn't help here). Direction of travel is determined in both systems by taking the difference in position over a known time interval. GPS can give heading by using the phase difference between receivers on different parts of the vessel, whereas the wavelength of LORAN was probably too long for that to work. Upshot is, a problem involving headings and direction of travel isn't the fault of GPS, and using LORAN would have been no defence. It may have been a problem with the GPS receiver software, but LORAN calculations could go wrong too. Most likely it was a navigator not understanding the systems they had.
Quidnam Latine loqui modo coepi?
Don't ships' navigators still train on sextants and chronometers?!?!?
I don't know if it's a holdover from my days as a boy scout or what, but I almost always have a backup, and a backup of the backup of anything critical to my survival. And if I ever get rich enough to own my own ocean-going vessel, *I* sure wouldn't put to sea without a sextant and the training to use it. And I'm just some not-a-professional-ship's-navigator schmuck.
Imagine all the people...
You can't draw that conclusion until you know what went wrong with the gps-based system, and what goes wrong with ground-based system. It's not as if the obvious alternative to a flawed system is using a perfect system instead, or even a (more complex) combination of systems.
I don't remember the detail of the story; However, the point of it being a failure due to GPS issue was relayed by my friend (the daughter). The vessel was a packer named "The Salty Isle" and is known by some in the BC area. The seafood-diver fleet was in the area and made a midnight storm rescue of all hands from a nasty rock.
I seem to recall that the amount of current in the passage (at night) was the problem, and that the drift was not noted by the Skipper with the GPS instrument because of a constant reading, whereas with their LORAN set, a drift would have been noted by a varying value. Ya can tear it apart and IANAGPSLORANO, sorry.
But do read Critical Path, it is worthwhile, including Fuller's description of a Geoscope which it seems Google Earth is modelled after.
It sounds to me like a cry for help directed to the public sector, from the US Government.
Imagine a subscription/license service for a geo-location broadcast platform from space that is unrestricted to users and as accurate as science knows how to make such things "accurate." How much do you think that license would be worth?
Scary? Absolutely.
Possible? More Absolutely!
There is serious money in geo-location today. Not just to target nuclear warhead.. if you call that a business.
Lindsay Blanton
RadioReference.com
> Thats why I never accept apologies. If they were really sorry they wouldn't have done it in the first place.
Wait. You think that John Paul II (or anyone else alive today) was the one who put Galileo on trial!? Or do you use that strange variant of the word "they" which lumps together both guilty and innocent alike (AKA "guilt by association").
Direction of travel is determined in both systems by taking the difference in position over a known time interval.
Sorry, I should have said velocity is determined in both systems by taking the difference in position over a known time interval. For direction of travel the time interval doesn't matter of course.
Quidnam Latine loqui modo coepi?
Direction of travel is not the same as Heading. Heading (the direction the vessel is pointed) can be different than direction of travel at sea, or in the air due to movement of the water/air itself.
Yes, because we broke out the Queen. Magnifico.
The World Wide Web is dying. Soon, we shall have only the Internet.
Sorry to say it but this is a complete load of @#$$e
Re: What happens if GPS fails(or gets turned off)
Other countries have asked this question post cold war when GPS was scrambled to be 100m accurate for end users.. as there are two Functional systems operating at this point in time.
GPS(Yanks)
GLONASS(Russians)
In test mode there is
The EU has 2 test satellites in their Galileo Constellation
and China has 2 test Sats in the COMPASS Constellation
India is also setting up there own geostatiary system
As per Quantity of Sats:
There is currently 30 GPS satellites in orbit and they are being updated all the time with the newer L5 and L2C signals to have a fuly functional system it is required to have 24 but there is a few spares up to enhance the system in poor environments. Not to mention Dual constellation GNSS systems that is used in Survey Construction and Ag already where in the southern hemisphere you see up to 19 sats at a time(Iâ(TM)ve seen once). Now imagine the urban canyon with that many satelites once recreational GPS takes up GNSS..
http://en.wikipedia.org/wiki/GPS_III
As per the accuracy of GPS..
That wonâ(TM)t happen due to the control segment dropping the ball as they have ground based monitoring on all of the different continental shelfs(eg Australia moves 70mm NE every year)
http://www.navcen.uscg.gov/gps/status_and_outage_info.htm
The biggest problem for recreational(single freq) GPS accuracy is the current solar cycle increasing the activity in the ionosphere as this is the key contributor to GPS being less accurate.
http://www.ips.gov.au/Educational/1/3/10
I had trouble finding the place... ba-dum-bump...:-) I'll be here all night folks -- try the veal!
USCG LORAN stations are still operating.
http://www.navcen.uscg.gov/Loran/default.htm
Not all the world is US, LORAN is being discontinued in many places due to GPS being "free".
Get a GPS system that also uses the European system. Europe put up their own satellite GPS system specifically because the US threatened to 'pull the plug' at various times. The EU uses GPS for navigation (ships, planes, rail, trucks, etc.). They wanted something that they could rely on, of their own. The US was quite sour when they announced the project, and was even more sour when deployment started here. Not being the only game in town means the monopoly is broken. Suddenly the US isn't the windshield, and the EU isn't the bug. Suddenly, things just keep working. Suddenly hasty American action only harms American citizens the most. A third system would help more. Maybe Chinese. You would get at least minimal service at all times.
Its about time there was some good news!!!
The governments increased inability to track me is good news indeed.
Direction of travel is called Bearing. A plain GPS device can give you bearing, but not heading. Many handheld GPS devices include a solid-state magnetic compass, though.
"(GPS gives time too, but that doesn't help here)"
You can derive time from LORAN. It just isn't up front about it like GPS.
"Upshot is, a problem involving headings and direction of travel isn't the fault of GPS, and using LORAN would have been no defence"
Sounds to me like the original problem, given neither GPS or LORAN does heading or direction of travel implicitly, is either in the interpretation by the device being used, or in the signal being received. If the former, that's the fault of the manufacturer.
To me though, it sounds like the latter, and if so, it most certainly is the fault of GPS (even though LORAN has its own set of issues) because it's implicit with older GNSS which includes GPS. GPS signals are not strong or always available or received being satellite and requiring lines to the sat. Yeah, people may THINK they are always getting a signal, when they get directions walking to a restaurant with their iphone or with their car's TomTom, but GPS signals often degrade, are weak, you can't find a satellite, etc.
LORAN is certainly not as accurate as GPS. Even eLORAN isn't as good as unenhanced GPS (it's very close). Still, LORAN is intended to be a backup, and being land based gives a more reliable and stronger signal to be received than GPS. It's the position info is crappy, and lots of things degrade it, but it's usually received.
It's a tradeoff, and why both systems should remain.
You don't have to be a professional navigator to use a clock and sextant. In fact, years ago, I have been in a situation where salt and water worked their usual magic on a brand new LORAN system (this was 10 years before GPS became available), so I had to rely on them for most of the long trip. But doing it the old way is nearly as good.
It's not so much fun in bad weather, though, when you can't see the sun, stars or horizon. Dead-reckoning is sometimes little better than guessing.
There's more than just GPS.
Here's a listing of all current/proposed global systems. Regional only systems such as IRNSS or Beidou1 are not listed.
GPS - United States - Fully Operation
Galileo - EU/China/Israel/South Korea/Norway/Etc - 2013
Beidou2/Compass - China - 2012?
GLONASS/ - Russia/India - Complete in 2010
http://en.wikipedia.org/wiki/Differential_GPS
What gives you the impression they're getting rid of ground stations?
Actual direction of travel is called course. A bearing is the direction from one point to another.
You can never go home again... but I guess you can shop there.
the main thing the USAF do, is dial in the time corrections to stop the satelites time drifting out of sync with our own time (this would cause them to be off by around 4km in a day if we didnt do the time sync) [see: BBC Horisons - Do you know what time it is], the thing is, this is done manually right now. surely there must be an algorithm that could work out what the new time code needs to be and automatically sync the satelites.
portfolio
Galileo has been marred with politics and other failures for a long time, and thus far is still vaporware. As of yet, there still aren't any birds in the sky. So yes, it would be great to have another system, especially since the US and EU apparently hashed out their differences and the systems will be interoperable, allowing receivers to use both to get even better accuracy and reliability. However as of this point, there is still much politicing and little satellite launching going on with the Galileo project.
So don't count on it until it happens. GPS remains important because it works right now, and almost all major transport has switched to using it as primary navigation.
They'll use something else if GPS has problems. When I was a surveyor's assistant, we never used GPS. Everything was done based on landmarks. You set a position on a known landmark, and used a digital theodolite to measure other points. This was done via a laser shooting to a reflective unit. The timing on the laser beam provided highly accurate distance data, the angles on the theodolite (and the known height of the pole the reflector was on) provided the necessary data to figure out the location of a point, relative to the known one. Gets you height too, as well as latitude and longitude.
This generally wasn't a big deal at all as survey markets are EVERYWHERE in most cities. They were plenty easy to find and use. Worse comes to worse, there are the original mile markers (the whole US has a grid of these) and you can start from there and triangulate to a new intermediate point.
Worked well for us.
We laughed at the fact that Europe has NOT stated to launch Galileo sats. As of yet, the system is still operational and I can't find any data saying they've even launched a single sat. Last I can see they were supposed to in 2H 2008, but I can't find anything saying they did.
The funny things about Galileo isn't that they are working on their own system. Makes good sense, especially since the US and EU apparently worked out their differences with it and the two systems will work together to give even better results. The funny thing is all the politicing and such going on that is keeping the project in vaporware status for a long time. By the original timeline, the system ought to be up now, and instead it isn't even starting.
...naming a bunch of things that orbit the Earth after Ptolemy... :-D
...or, coming at it from a different slant (closer to yours), maybe Copernicus or Aristarchus
Yes, I know about yaw. Which is why I said direction of travel is determined by comparing successive positions, and heading is determined by comparing positions of receivers on different parts of the vessel. I don't know of any vessels that use the latter system, but I've seen it presented at GPS conferences.
Quidnam Latine loqui modo coepi?
or at least very unlikely that any national institution would cry out for help like this, meanwhile disguising the fact that they just want more money ???
Free speech was meant to be free for all... how can anyone grow up in a nanny state ?
using static ground stations like LORAN,
Reminds me of something I've not yet found the answer to: Why don't we have ground-based GPS transmitters in addition to the satellites? - wouldn't this give improved reliabilty / accuracy / easier-maintenance in places where you need it (ie. near ports) with standard GPS receiver equipment (rather than needing extra equipment like for differential-GPS)
We have a GPS Accuracy Gap, fire up the PorkMobile, Taxman!
There is. It's called WAAS
Hell yeah. You never know when you're going to drop it / run the batteries down / lose it / sail into a mountain shadow and lose signal / get too close to a nuclear explosion and get EMPd.
Interestingly, recently sailing in my father's new yacht (a Hunter Liberty 23 twin masted ketch, lovely boat), when I wanted to know where we were in a hurry, my immediate reaction was to grab the hand-bearing compass and take a couple of bearings off nearby rocks. The whole process took about 20 seconds. I'd completely failed to notice the GPS hanging next to the compass.
The compass, BTW, floats. The GPS doesn't.
Someone didn't have RAIM.
Last I checked (about 3 years ago), SOLAS regulations had quite a bit about using GPS as a primary navigation system. At that point, I think it was still not permitted to be primary unless the system met very specific reliability and integrity monitoring requirements.
retrorocket.o not found, launch anyway?
What technologies are you talking about? I don't know of anything that's been developed entirely since the beginning of the Iraq war.
No, WAAS is satellite based and only provides correction signals used to improve accuracy of GPS measurments.
Speaking of cold war, my late father-in-law was an inertial guidance system engineer. He designed gyros. Remember the whole business about gimbel lock in Apollo 13? That was one of the gyros he worked on. One time he visited the naval air station at Alameda with a portable inertial guidance device, and discovered that the base didn't know where it was. The coordinates the base had were hundreds of meters off.
I was in on some early uses of GPS and maps, and let me tell you that maps based on the old surveying techniques can be wrong, particularly in coastal areas, because of failure to account for local gravitational anomalies caused by the variations in the thickness of the Earth's crust.
In any case, it sounds like positional accuracy wouldn't have been the issue. No GPS device can give you a heading. I don't know too much about LORAN but I think it works on similar principles; it doesn't tell you which way you're pointed. The GPS system doesn't give headings, but the device can interpolate a a "speed and heading made good" by looking at the trend in fixes. I believe LORAN works the same way.
In any case, such calculations can't be relied upon in coastal areas, precisely because of currents, which change from place to place. The pilot of a vessel who runs aground because he relied on GPS is still at fault because you shouldn't rely on GPS in such places.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
That's why there are VORs. Pilots use them all the time. They are ground based beacons for direction finding and ranging. And they're not going away.
Last I hear the Military was working on something better than GPS. The Navy in particular was looking for a system like GPS but much more accurate (so they could auto-pilot a jet landing on a aircraft carrier at night in rough seas). GPS is just not accurate enough for Military needs. Even in the last large offensive the GPS guided bomb where something like 6-9 YARDS to the target. Due to many reason the military/navy want and need something way more accurate. The GPS served the purposed but they are looking to the future and will let the current GPS system trickle into the control of the private sector.
I haven't had time to check every point in this article, but it fits with everything I've read about the subject.
Either way, you're either totally ignorant, or completely full of shit. According to the GAO, approximately 25% of "defense" spending is unaccounted for. This is probably by design to allow for the operational budget of the CIA, which is unconstitutionally hidden from the eyes of the public.
Once in Iraq, there was virtually no accountability over how the money was spent. There was also considerable money "off the books," including as much as $4 billion from illegal oil exports. The CPA and the Iraqi State Oil Marketing Board, which it controlled, made a deliberate decision not to record or "meter" oil exports, an invitation to wholesale fraud and black marketeering.
Thus the country was awash in unaccountable money. British sources report that the CPA contracts that were not handed out to cronies were sold to the highest bidder, with bribes as high as $300,000 being demanded for particularly lucrative reconstruction contracts.
The contracts were especially attractive because no work or results were necessarily expected in return. It became popular to cancel contracts without penalty, claiming that security costs were making it too difficult to do the work. A $500 million power-plant contract was reportedly awarded to a bidder based on a proposal one page long. After a joint commission rejected the proposal, its members were replaced by the minister, and approval was duly obtained. But no plant has been built.
Where contracts are actually performed, their nominal cost is inflated sufficiently to provide handsome bribes for everyone involved in the process. Bribes paid to government ministers reportedly exceed $10 million.
Money also disappeared in truckloads and by helicopter. The CPA reportedly distributed funds to contractors in bags off the back of a truck. In one notorious incident in April 2004, $1.5 billion in cash that had just been delivered by three Blackhawk helicopters was handed over to a courier in Erbil, in the Kurdish region, never to be seen again. Afterwards, no one was able to recall the courier's name or provide a good description of him.
...and was shit-stormed by /. and moderated as troll. This problem is hardly new. The problem has been on-going for a long time. After all, some of these satellites have been in place for almost two decades. That's a long time for an operational satellite.
Thankfully we now have systems like WAAS and AGPS to improve accuracy for civilian use. The problem with WAAS is its not likely your going to receive a consistent signal on ground. Its really designed for aircraft use. But given the right environment, its still possible to receive it.
The military still has other options as long as they can use multiple receivers. Not to mention other countries are starting to provide coverage with their own systems. I fully expect the military to leverage these where applicable - at least for munitions and possibly ground forces.
And to the ignorant mods and /. out there than wanted to make sure everyone remained as ignorant and dumb as them - F-U! Hopefully you feel like a first class jackass now. Maybe next time you'll not moderate things which are obviously well outside of your body of knowledge. Doing so only makes everyone as ignorant as you.
LORAN and GPS provide the same information. The best I can guess here is the LORAN receiver provided more information than the GPS receiver. For example the LORAN displayed the intended course and the GPS didn't. This isn't a GPS problem. It's a user problem.
Disclaimer: I'm a defense contractor. Some points in response:
First of all, I'm not sure how you're defining "defense" spending, but it's worth noting that the CIA is not part of the DOD, and they have their own budget. GAO is almost certainly talking about the DOD budget here. There are obviously black programs within DOD, but they're nothing close to 25% of the budget.
The real issue here is DFAS (the Defense Financial and Accounting Service). These are the folks who are responsible for (among other things) paying the defense department's bills. And they get graded on how fast they do it, not on how accurate they are. As a result, they frequently end up paying invoices out of the wrong accounting lines... which, in the end, means that you can't figure out where your money went.
I see this with my (DOD) customers all the time. We do work, properly charge it against the right accounting lines, and submit our bill. Months down the line, the customer comes back and says things like: "Why didn't you expend all the funding on the XXX project?". I look over the records, and find that we've expended, billed, and been paid for XXX already. My only response is that they'll have to ask DFAS what happened, because all I know is that we got paid for it.
The rest of your post discusses problems in Iraq. But most of this has to do with extreme, borderline criminal negligence on the part of the gov't people who should have been overseeing funds distribution there. Almost every aspect of the disaster that was the occupation of Iraq, was, well, a disaster, so it's no surprise the financial aspects of this were screwed up too.
Yes, there are DOD contractors who are crooked. But the vast majority of problems with the inability to account for government funding is that the DOD accounting service is just not very good.
That's right. And neither GPS nor LORAN has the capability to measure heading (only a compass can do that), so I'm calling BS on this story.
There are more and more ships using GPS based heading sensors. They tend to be a lot larger and more expensive than your older style compasses, however.
It's not hard to derive heading from GPS if you use two sensors in known positions of the vessel. Each one can tell where it is at on the earth, and since you know where you put them on the ship, you can derive the vessel's heading.
You're Welcome.
I'm really surprised that there has only been the ONE mention of GLONASS. GPS/GLONASS receivers have been available for years, but with collapse of the USSR, GLONASS almost became totally useless.
Now however, they've been launching 6 satellites a year and have a nearly full, and quite usable constellation. The accuracy is not quite as good as GPS and it's a much harder system to work with, but, quite useful shoudl anything happen to GPS.
Sorry, I should have said velocity is determined in both systems by taking the difference in position over a known time interval. For direction of travel the time interval doesn't matter of course.
Sorry, wrong again. For GPS, speed (not velocity) is derived, not by taking two positions and a time interval, but rather directly from Doppler shift between the receiver and the satellite.
In the interest of complete precision, velocity DOES include direction. It's a vector and includes both magnitude (here of speed) and direction.
That's why a point on the edge of a disc rotating at a constant speed is said to be constantly changing velocity. The speed remains steady, but the directional component is constantly changing.
No, I was right -- read what I wrote. The original posting related to course ("direction of travel"), so I was concerned with velocity, not speed. And velocity is derived by comparing consecutive 4-d positions.
Quidnam Latine loqui modo coepi?