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What is the distance between the closest gps positions?

If I have multiple devices and I want to get their locations, these devices being within a 20 meter radius, how accurate will the coordinates be?

e.g how close do players need to be before the coordinates are the same?

Thanks

some_id
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1 Answers1

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When you query a location via CoreLocation, you get the accuracy in the CLLocation instances. See the horizontalAccuracy and verticalAccuracy.

The accuracy of GPS depends on a number of factors like signal quality (for example, signal quality drops if it's cloudy). Also, the iDevices differ in their GPS receiver's accuracy. I found the iPhone 4 to be more accurate than the iPhone 3G, for example (the iPhone 4 also seems to have a better antenna as I often get a signal with iPhone 4 where the iPhone 3G is having a hard time).

DarkDust
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  • Great, thanks. but also, how much distance is there between a gps location? If multiple devices are within a 20 meter radius, will they all have different gps locations unless there are devices in EXACTLY the same spot? what if a device is 1 meter away from another 1? thanks – some_id Jul 04 '11 at 10:50
  • For *"how to calculate the distance between two GPS points"*, see [this SO question](http://stackoverflow.com/questions/365826/calculate-distance-between-2-gps-coordinates). It's up to you when to treat two points as being in the same spot. The [GPS accuracy](http://www.geod.nrcan.gc.ca/edu/geod/gps/gps13_e.php) can reach down to the 1cm level with the right equipment. Usually GPS in devices like the iPhone are subject to various signal quality problems and if you put two iPhones next to each other they may show positions which are off by a few meters. It really depends on the weather. – DarkDust Jul 04 '11 at 11:47