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back to article Moneybags pour shower of gold on new mega-precise GPS system

A GPS-based satellite navigation system promises accuracy to within an inch by December this year – to those willing to stick a thousand dollars into the pot. Swift Navigation, makers of the super-accurate satnav, say it uses existing Real Time Kinematic (RTK) navigation techniques to ensure its pinpoint accuracy. Rather than …

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this sounds a lot like Differential GPS..

but with "phase" detection...?

D-GPS has been around for years, and did ~10cm accuracy- IIRC

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Anonymous Coward

Re: this sounds a lot like Differential GPS..

Might be this? http://en.wikipedia.org/wiki/GPS#Carrier_phase_tracking_.28surveying.29

Not new either, but it has been jolly expensive in the past and probably covered in patents, too. It is a neat trick, but it has a bootstrapping problem, in that the additional accuracy is relative to the fixed base station. If you don't have a nice triangulation point that's been carefully surveyed to a high level of accuracy, your extra levels of precision might not be so useful.

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Paris Hilton

Re: this sounds a lot like Differential GPS..

Ahh, but to some people 4 inches is a lot!

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Silver badge

Re: this sounds a lot like Differential GPS..

RTK isn't really even GPS, it uses GPS as a convenient high precision signal and tracks the phase difference between the base station and rover.

It has been around for years but the normal customer is high end surveying so the units are rare and expensive.

There has been an open source system for a few $100 that runs on a beagle board and a cheap SIRTF GPS chipset. You just need a GPS chip that gives you phase information, a cheap linux box and a comms link between the base and rover.

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Anonymous Coward

Re: this sounds a lot like Differential GPS..

"Ahh, but to some people 4 inches is a lot!"

It certainly is - considering we're probably talking radius!

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Anonymous Coward

Re: this sounds a lot like Differential GPS..

It might be that, though there seems to still be much handwaving with weasel words like probably and likely and numerical techniques like least squares fit (other curve fitting techniques are available, and occasionally more appropriate).

If the solution can't be described with a couple of 555 timers, and/or a Kalman filter, and more recently a Raspberry Pi and three lines of python, it's probably BS, or at best, someone else's patented BS.

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But you need two of them to get that accuracy

And I don't see how they can compensate out ionospheric effects to that level of accuracy using only a single frequency band. Better to use the Galileo signal, which runs on both the L1 and E5 bands at the same time.

Differential GPS relies on a reference base station in the local area, so you don't get coverage in large chunks of the world. IIRC the clocks on board of the GPS cluster aren't accurate enough to go beyond that (though the latest block satellites may have fixed that).

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Len
Boffin

Re: But you need two of them to get that accuracy

Yep, and Galileo is accurate to 1 CM...

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Anonymous Coward

Re: But you need two of them to get that accuracy

"Differential GPS relies on a reference base station in the local area"

Certainly does. The 2013 farming article Bill references says all the finest New Holland tractor dealers will have them.

But it actually seems like RTK's been around since 2007 (if not earlier).

http://www.profsurv.com/magazine/article.aspx?i=1837

Although the Wiki article on RTK is (imo) entirely free of meaningful content.

Imo, anything claiming to rely on identifying RF phase (rather than relative phase of two distinguishable signals) has to be treated with great scepticism. Maybe it's just that the descriptions have lost something along the way.

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Silver badge

Re: But you need two of them to get that accuracy

Checking further it seems that RTK is only accurate to centimetric accuracies for RELATIVE positions. It needs at least two GPS receivers, one of which is a fixed base station. The accuracy of the fix for the base station limits the total accuracy of the system.

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Re: But you need two of them to get that accuracy

For a very many uses (most I can think of), relative position is fine. Eliminating drift is the key to more accurate usage. My drone doesn't care exactly what altitude my back garden is, so long as it's the same as when it took off 20 minutes ago. My tractor doesn't need to know precisely where that oak tree is, so long as it doesn't suddenly jump 3m to the left. Even for land surveys, they're normally done with reference to a landmark (corner of a plot, known location of another building, etc) so they would be pretty much fine with this too - that's how they already work with DGPS.

I suppose there may be some situations where absolute location is important, for example lane guidance in sat-nav units, but for them the existing accuracy seems fine already.

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Happy

Re: But you need two of them to get that accuracy

High precision D-GPS sees quite a bit of use in construction, precisely because that oak tree does move and the altitude of the construction plane does change.

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Anonymous Coward

sounds quite clever. I remember doing all this stuff back in the early 90's as part of my marine studies degree (did a bunch of hydrography modules so had lots of navigation content) One of our lectures at the time, an ex hydrographic surveyor, went over to a marine institute in Russia on an exchange trip he took a look at GLONAS the Russian equivalent of GPS. Whilst GPS kit was quite small even in the early 90’s the GLONAS kit was about eh size of a filling cabinet

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Coat

@Anon. cow. 09:35

The correction for light speed in the atmosphere is interesting. Light speed varies with density of the atmosphere, does it not? Given global warming, is the correction updated as the atmosphere warms?

No, mine is 36 centimetres to the northwest.

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Anonymous Coward

"Turn right in 582,363 millimeters."

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$14k

Is what I don't get.

14k isn't enough to fund development if they haven't already done it. It isn't enough to fund a volume production batch to bring the unit cost price down.

The campaign is good publicity but otherwise seems to be a bit of a waste.

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Silver badge

Re: $14k

I thought the money was for production, they already have working units.

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The clue is in the K

Kinematic. It works on the move. Standard surveying techniques using GPS work best with fixed stations occupying a site for a while. You can get millimetre accuracy doing that & track continental plate movement. RTK, as has been said, has been around for a long time but at silly prices. Some early 'Consumer' GPS receivers would give raw carrier phase output and, with the right software, would give quite good results. I played around with a Garmin receiver and RINEX files from the Ordnance Some years ago. Unfortunately most consumer GPSs have now lost that facility, probably for market differentiation reasons. However, RTK needs better receivers to allow to track the carrier phase without phase slips whilst on the move. If this crew have cracked the cost issues for doing that then this could be quite interesting. It still needs a local fixed reference station on a known site (to the millimetre) to work properly though.

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Yawn

My micro-drone uses GPS together with three axis gyros and accelerometers to know where it is within centimetres and only using a cheap non-differential GPS board.

What people generally don't realise is that GPS at a fixed location wanders continuously over several metres - sometimes tens of metres - due to constellation changes and ionospheric changes.

Differential GPS fixes this up a lot, but single point GPS with INS and cool algorithms works just as well.

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Re: Yawn

Yes, but your absolute position could be anywhere within the ~10m GPS error ellipsoid if INS slaves off GPS initially. INS systems on aircraft can be initialised on the ground to the exact aircraft location, which is painted on the hard stand or a signpost where it parks.

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Bronze badge

within an inch?

When I was surveying in ~2005, it was possible to obtain quarter-inch accuracy with GPS if there was a CORS station (basically another GPS at a known location, logging its deltas online) within several miles. This was high-end gear, of course.

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But will it

work inside a building?

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