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Geek Culture / How accurate is GPS?

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Chris K
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Location: Lake Hylia
Posted: 8th Apr 2008 14:10
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I am going to buy a GPS receiver for a few programming projects, and I know people always say that they are accurate to about 15 metres, but is that error random or systematic?

Basically, for the two things I am making, I just need to measure accurate changes in position; I don't care if it is telling me I am in Russia, as long if I move 1 metre to left, it tells me I am one metre closer to Moscow or whatever.

The two projects are a speedometer for a rowing boat and a GPS enabled camera to build a library of location-tagged photos for trying to make a photosynth style 3D tour of a town.

For the camera thing I guess I can stand still for a while and let it average out the readings...? TomTom speedos seem pretty good at getting the speed (it comes out slower normally because car speedometers have to say the speed faster by law)

I'll probably just buy one for mucking about with, they are only about £25 nowadays (as in, the raw receivers not an actual navigation system). I've also got an O2 XDA, which has Bluetooth, that's what I'm intending to make the rowing speedo with.

-= Out here in the fields, I fight for my meals =-
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Kentaree
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Location: Clonmel, Ireland
Posted: 8th Apr 2008 15:00
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It really depends where you are, and how many satellites the device can acquire, the more, the better the accuracy of course. 15 Meters seems very low accuracy to me, even car navigation systems would have problems dealing with that level of inaccuracy in cities.
I'm about to start a project very similar to yours (involving a handheld + bluetooth GPS receiver), so I'll be interested in knowing how you get on.

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Chris K
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Location: Lake Hylia
Posted: 8th Apr 2008 15:15 Edited at: 8th Apr 2008 15:15
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This seems like a pretty good buy:
http://search.ebay.co.uk/_W0QQsassZhytekltd

Works out about £25 with P+P, good reviews, good specs...

Have you got any experience in programming for handhelds or using Bluetooth? I don't!

I think there's a free SDK for WindowsCE, that's what my XDA has.

-= Out here in the fields, I fight for my meals =-
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Digital Awakening
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Posted: 8th Apr 2008 15:20
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Apparently you can get it down to 30 cm of accuracy. I didn't read through it all though, seems like there's a bunch of things messing up the readings.

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the_winch
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Location: Oxford, UK
Posted: 8th Apr 2008 20:10
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I'd say sub 10 metre accuracy is probably what you get in good conditions. However if you where to drive down a road then turn around and come back you generally get two district traces, one for each side of the road. Working out where you are on the earth appears less accurate than working out you moved 5 metres.

Reliably detecting you moved 1 metre is really pushing it. Your position jumps about a bit when you are stationary. Perhaps old fashioned surveying techniques would work better. Find something with a known position and use it as a reference to calculate your position when taking a picture. I expect that would involve a lot of boring work.

The speedometer for a rowing boat is defiantly possible. You might be able to find an off the shelf product that does all you want. There are gps devices aimed at runners and cyclists, for example.
http://www.garmin.com/garmin/cms/site/uk/ontofitness/

By way of demonstration, he emitted a batlike squeak that was indeed bothersome.
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kaedroho
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Posted: 8th Apr 2008 20:33
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Quote: "Apparently you can get it down to 30 cm of accuracy."


Ive heard about a few milimetres somewhere.


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Wiggett
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Location: Australia
Posted: 8th Apr 2008 20:37
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my phone does gps with accuracy of 3 meters.

Syndicate remastered: Corporate persuasion through urban violence.
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Osiris
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Posted: 8th Apr 2008 21:26
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You can get within an inch. If your the military.

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You will be dearly missed.
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Chris K
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Posted: 8th Apr 2008 23:47
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@ the_winch

Yeah, the fanciest CoxBox's (the clock/metronome/microphone thing a cox has) have GPS in them, but I was looking to make one on the cheap... Seeing as I already have an XDA.

-= Out here in the fields, I fight for my meals =-
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El Goorf
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Posted: 9th Apr 2008 02:20
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im not sure gpu is accurate to be able to say which side of the road you're on, it works by working out which direction you're travelling, not location relative to the road's centre..

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GatorHex
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Location: Gunchester, UK
Posted: 9th Apr 2008 02:35 Edited at: 9th Apr 2008 02:37
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Mine is within a couple of meters as far as distance accuracy goes.

But if by accuracy you mean do they know which way to go then buggerin hell no they send you miles off route sometimes or shortcuts up roads no billy goat would go

DinoHunter (still no nVidia compo voucher!), CPU/GPU Benchmark, DarkFish Encryption DLL, War MMOG (WIP), 3D Model Viewer
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