Cellphone GPS accuracy poor?

So, I converted the GPS stamp in one of my photos into a map location. Now, assuming that you can trust Google Maps (I think that’s fair), and that with the photo in question I know where I was to within about 10 feet, the GPS stamp in the picture is about 4000 feet away.

From Google maps, my latitude and longitude at the time of the photo was 33.6588 -117.7668. But the GPS stamp in the photo says

GPS Latitude Ref : North
GPS Latitude : 33 deg 38' 59.40"
GPS Longitude Ref : West
GPS Longitude : 117 deg 45' 60.00"
GPS Time Stamp : 13:32:53.72
GPS Img Direction Ref : True North
GPS Img Direction : 171.6590909

which, if I do the math, is 33.649833 -117.76666.

Is Google Maps that far off? Or did I do the math wrong? I think I did the math wrong. Also, other people think that GPS locators in cellphones can be drastically off some of the time.


is an article about Shopkick’s experience in correlating GPS location from the cellphone with a known location.

This is strange, considering that GPS itself is pretty darn accurate.

http://www.gps.gov/support/faq/ and http://www.gps.gov/systems/gps/performance/accuracy/

Given the time I took the photo, this would have been with my iPhone 1, purchased the first day iPhones were available. Maybe the GPS has gotten better in newer models? I’ll need to test.

Ah, maybe it’s an indoors issue? Apparently, GPS signals are partially blocked by building walls, so the accuracy indoors is degraded. That sucks, considering that a lot of my photos are taken indoors. http://stackoverflow.com/questions/4424387/how-accurate-is-the-gps-on-the-iphone-4

Also see this: http://academics.skidmore.edu/blogs/onlocation/2012/03/smartphone_accuracy/. For outdoors, an iPhone is ok to several meters, outdoors.

And apparently the iPhone 4 has a vastly improved GPS receiver. Time to upgrade.


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