iPhone GPS accuracy

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astroboy

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#40096 25-Aug-2009 13:25

Hi,

I'm wondering if my GPS issues are typical of the iPhone in general or my particular one. The iPhone GPS never seemed to be particularly accurate, but it was close enough for my use. It would rarely locate me at home, unless I was driving and happened to pull up in my driveway. Since then, I upgraded to OS 3.0. Now it gives me a location several blocks from my home, and never seems to give an accurate location (I live in Wellington). I installed a free GPS app (MotionX-GPS Lite), but it never seems to hook up to a GPS satellite (it has a searching for satellite scrolling message). I'm interested in the TomTom app, but not if it's a waste of time. So I guess my question is: do other people find their iPhone GPS reasonably accurate (a few metres)?

Thanks

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#250351 25-Aug-2009 13:59

Mine is pinpoint. Make sure u are outside clear skys etc it doesn't work well inside structures, I think that goes for most gps's.

When gps isn't available (indoors) it uses triangulation which works ok for me...can be out by a block or so.

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LennonNZ

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#250365 25-Aug-2009 14:28

I must ask. if you go outside so you can see the sky.. does the GPS work correctly?

freitasm

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#250410 25-Aug-2009 16:12

astroboy: I'm wondering if my GPS issues are typical of the iPhone in general or my particular one. The iPhone GPS never seemed to be particularly accurate, but it was close enough for my use. It would rarely locate me at home, unless I was driving and happened to pull up in my driveway.

You do know that GPS requires clear view of the sky to get a good sattelite signal, don't you? GPS signals are very very weak, and it won't work inside houses, buildings, under viaducts, within tunnels, sometimes even under heavy tree tops.

What your iPhone gives you while inside the house is an approximation based on the cellular network timings. It's not accurate at all, therefore it can be any point within up to 3000 meters.

With full signal lock most GPS will give your position within 3 - 20 meters with no problems.

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CJPhoto

73 posts

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#250456 25-Aug-2009 18:34

It can also use your wifi connection to find your location if registered with skyhook. I registered my home wifi as my cell tower seems to use one across the auckland harbour sometimes.

astroboy

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#250463 25-Aug-2009 18:44

Ok, went for a wander down Customhouse Quay - it'pretty open, with no tall buildings in the way. The GPS placed my on Lambton Quay, which is a copuple of blocks away. Plus my location pin didn't move on the map with me.

BTW - it should work when I'm in my car, right? It's not much use to me if it doesn't...

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#250470 25-Aug-2009 19:04

Yes, it should work while in the car - on the console or on the passenge seat. Not if inside a bag or backpack.

A GPS unit needs to get a "lock" on at least three satellites to get accurate readings. If this is the first time using it then you should wait up to five to ten minutes so that the unit can scan the sky searching for different signals. After this it should get a good lock in a matter of seconds.

This is a problem too if you use it here in New Zealand and go to the U.S. or Europe. The GPS is expecting signals from some areas in the sky but the satellites over there are in different positions.

As you see it's all very scientific and if you don't wait you don't get the benefits.

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JKRNZ

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#250529 25-Aug-2009 22:12

And to really confuse matters you will be using the civilian GPS calculations. These give a latitude and longitude that don't match the true physical position on Earth. For true accuracy only the military have access.

freitasm

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#250536 25-Aug-2009 22:47

The GPS Selective Availability was turned off in 2000 by Presidential orders. It means that civilian use of GPS is now many times more accurate than before. Usually you get accurate readings up to 3 meters.

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#250544 25-Aug-2009 23:21

I have never found gps to be inaccurate, except for back in the days when civilian signals had selective availability errors it used to only be reasonably accurate but I have found even basic devices (N95, 6275, htc libra, palm treo pro) to be extraordinarily accurate to less than a metre as demonstrated by an outdoors trip in the weekend just been locating disused structures and way points previously marked.

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#250557 26-Aug-2009 00:55

Im a geocacher and so far I have found the Iphone reasonably accurate in pinpointing your location. But this appears to depend on what application you are using at the time which ill explain later.

I use the geocaching.com application when im out in the field and also a Dedicated Garmin Colorado 300 which is one of the top of the line Hand held units. Where I can get supposedly 4 Mtrs accuracy. Sorry I am digressing.
Back to using the Iphone-in the field, looking at finding the cache in an open sky situation the compass part of the app tells me I have 17 Mtrs accurracy. !! Takes a bit longer to stabilize than the dedicated unit.

I use the Tom Tom map application and practically I find it pretty bang on the mark with locating you and giving you timely directions-even in overcast skies. Just the map data is a little out of date. !!
Occasionally I have noted and it seems wierd considering what ive been saying about accuracy but the native Iphone map application appears to show me as being somewhere slightly different. But not as bad as using say Google Lattitude which is often quite out by a block or so. Yet using an app called Brightkite which is a location based Twitter client it shows me as pretty much bang on !!
So there we are a fairly lengthy post about my experiences using location based services on the iphone which I have promised to blog about.
In general its acccurate, give the unit a bit of space as Mauricio suggested and 10 mins then check.
If not then there is something wrong with your unit by the sound.
Hope you find this post useful.

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consolation

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Master Geek

#251652 30-Aug-2009 02:59

Here's something a bit odd that I noticed when in Welly for a few days, couple of weeks ago. It took far longer and the location was far more inaccurate than in Dunedin or Queenstown where I usually reside. It took a few minutes to lock onto a gps signal and in some places the accuracy never got better than 17m. In the south island, I find it locks on within 30 seconds max, usual accuracy is 4m iirc. Break out the tinfoil hats people...

SiiriW

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#256462 17-Sep-2009 12:45

Hi there, I have the same problem as astrobay. I used to be able to use my iPhone in the car as a map, presetting the route in Maps and just following the "blue dot".
Since upgrading to OS3.0 it doesn't work anymore. My position is rarely picked up while I'm walking out of town, and NEVER in the car. The phone only picks up the closest cell phone tower, but not my position.
This is very frustrating as it used to work a treat. Now it's pretty useless as a map/gps system and I had to revert to paper maps...
Any help on how to restore the phone functionality would be greatly appreciated.

CJPhoto

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#256463 17-Sep-2009 12:50

Have you tried resetting the device?
(standard IT help desk reply/joke)

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#256467 17-Sep-2009 12:52

astroboy: BTW - it should work when I'm in my car, right? It's not much use to me if it doesn't...

No, the official word with GPS is something along the lines of "it should work when you have a clear, unobstructed view of the sky."

Many vehicles have a windscreen that is slightly tinted or treated for various reasons (vision, integrity etc), and apparently some of these coatings and particles can interfere with GPS reception.

For what its worth, in the middle of my lounge, and the middle of my bedroom, I get excellent GPS reception on my E75! But that is rare from what I gather, and I wasn't as lucky with other GPS units I have tried.

ddn

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#256652 17-Sep-2009 20:28

freitasm:

This is a problem too if you use it here in New Zealand and go to the U.S. or Europe. The GPS is expecting signals from some areas in the sky but the satellites over there are in different positions.

Ah, this explains why I couldn't get a position reading when I visited Sydney a couple of weeks ago. I tried for at elast 5 minutes to no avail. I did have data turned off as I didn't want any roaming charges and someone has told me that because its AGPS it needs the datw connection, but I'm not sure this is correct -- I've been out in the bush before with no connection and I had a good lock.

And my iphone with a clear NZ sky pinpoints me very well - within 3 or 4 m I'd say. I use it for geocaching too. Good fun.

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