Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

I'm working with Android and iOS apps that report location. Both iOS and Android can derive location from a combination of cell tower triangulation, visible wifi access points, and assisted GPS. The location APIs return a lat/long and an "accuracy" number in meters. In the case of Android the API also tells us whether GPS was used, but iOS does not report the source.

What I have not been able to figure out from the Android/iOS documentation is how to read the accuracy number in terms of probability. Some GPS devices return the CEP, which means that there's about 50% probability that the device was within that radius. There are other ways of describing accuracy (e.g. 2DRMS) that provide up to 98% probability.

Is there any standard for reporting these accuracy numbers in Android and iOS? Or would the probability of the device being within the accuracy circle vary from one reading to the next?

share|improve this question
add comment

1 Answer

The same question (for Android only) was asked on the main site: http://stackoverflow.com/questions/3052517/how-is-location-accuracy-measured-in-android

The only relevant piece of information is in paracycle's comment, which shows he actually inspected the code, which seems to be passing CEP directly from the hardware.

share|improve this answer
    
thanks for pointing that out. It seems that the meaning of the accuracy number depends on the hardware--for GPS readings we're likely to get CEP, whereas cell-tower readings don't always look like they are probabilistic. I have seen some location readings where the lat/long is the location of a cell tower and the accuracy is exactly 1000 meters, and all the readings from that vicinity were like that. –  Matt Jun 18 '12 at 18:37
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.