Spanish boffins increase GPS accuracy by 90% Boffins at Madrid's Carlos III University have used cheap accelerometers and gyroscopes - and expensive mathematics - to improve the accuracy of GPS* by as much as 90 per cent. The team compared their results to differential GPS - which is about as good as satellite systems get - and found that with detailed analysis of the …
"outperforming differential GPS by a significant margin"
Real-time DGPS will give you centimetre accuracy, how does this system outperform DGPS?
"drift caused by atmospheric changes"
Discrepancies due to time sync differences between satellite and receiver clocks, arguably, is equally important, and definitely worth mentioning if you start explaining GPS (also uncertainty in ephemeris, satellite geometry and, being pedantic, general relativity)
Don't forget to mention that GPS is an American military system and that they can and do program the satellites to deliberately degrade system accuracy. There is also two parts to it - the open code signal that is often quoted as having 10 metres accuracy, and the secret code signal that is more accurate but not generally available to all users.
I think the Register hack was told to write a description of Differential-GPS in the footnote, but he bottled it.
1) The Amerixcan military moved away from degrading the unencrypted signal on GPS years ago. The unencrypted accuracy is the same as the encrypted. The limit is pretty much physics now.
2) They have actually removed the degradation feature from new satellites added to the constellation - as the older satellites go out of use, this option becomes less and less possible.
3) The reason the Q code is encrypted is not secrecy. It was assumed when GPS was designed that the Russian equivalent would be up and running rapidly. The Q code is there to make it harder to jam (lock on the signal when jamming is actually louder than the signal - think listening for a known tune) and to make it very, very, very hard to spoof (you would have to know the code to broadcast a fake signal).
I disagree, sir. The secret code version is about ten times more accurate, or at least has the potential to be. They used to boast about being able to put a cruise missile through a window. Also, its not difficult to jam at all.
You are probably right about them not bothering with selective availability any more.
But WTF I get three downvotes for an ordnary post like that?
I recall driving through the Limehouse Link tunnel and then between some tall buildings along London Wall one day, in 2010 I think, and noticing the loss of satellite signal, and remembering that my then-new iPod Touch could tell which way up I was holding it because of digital accelerometers. I recall mentioning this via email to a TomTom engineer ... "with a couple of orthogonally-arranged accelerometers, you could achieve inertial reference navigation, as a secondary position source when GPS reception keeps dropping out", and the reply I got indicated that this was a newly-introduced feature on top-spec models.
It's been a part of the Prius sat-nav since, ooh, about 2003. Inclinometers and gyroscopes which form part of the anti-skid system, augmented further by the high precision axle rotation sensors which the hybrid drive requires (you have to manually calibrate the nav system every now and again to allow for tyre wear which is best done on a long, straight motorway), and a position sensor on the steering shaft, which is part of the electrically-power-assisted steering.
Still that's all expensive stuff and even then brings the accuracy down to only a metre at best.
I saw a presentation by the guy from BAE who wrote the system which uses "Signals of Opportunity" (TV/radio transmitters and mobile masts), that is seriously impressive, seriously cheap and self calibrating. This proposal seems to tackle the same problem from a physical environment perspective.
In respect of the 2m accuracy killing people, I think if autonomous car designers used street maps alone for their navigation it would be very optimistic. Better to use a range of tools, like this one, combined with collision avoidance, road marking recognition, environmental awareness, etc.
"Better to use a range of tools, like this one, combined with collision avoidance, road marking recognition, environmental awareness, etc."
Yes
Might it be better to look at not hitting stuff within 2m of the vehicle as "collision avoidance" rather than navigation?
Different response times, different range.
Remember my boss telling me this: A sensor on one of the gyros failed. Decouple it, stick it in a straw-lined box (still spinning) and courier it back to the manufacturer. (Gawd knows how the driver took a corner!)
They'd get it 2 days later - stil spinning - , change/fix the sensor, spin it back up to full speed again, then return it to the boat. 2 days later, still spinning, fit it back. Bloody thing was still accurate to about a metre....Dunno if he was casting me a line, but...
I can definitely see two meters resulting in cars pushing into crosswalk areas and pushing over pedestrians, or nosing too far out into an intersection before making a turn and getting the front of the car taken off by a semi...
Stop sign icon works on a few different levels in this case......
I worked for one of the companies doing high accuracy GPS for 12 years.
With RTK GPS, you can get 20mm - yes folks - less than an inch accuracy and we could control the steering of tractors etc down to better than 150mm (6 inches). With DGPS sub-metre has been possible for many years too.
These are absolute accuracy, but when you're controlling a vehicle, drift is far more important and you re-reference from other cues.
Modern self driving vehicles would never use just GPS. Instead GPS is just one of the sensors being "fused" into an effective solution.
This is definitely not new. I know of at least one company who did work on this over 10 years ago. There are also many articles about using Inertial (gyro + accelerometer) aided tracking with GPS. One company that I know of is Cubic Defense Applications Inc. Look up "GPS denied tracking" on Google. The inertial devices being used were not high cost/expensive. They were MEMS devices...
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