How accurate is the GPS on the iPhone 4?

Question

quick question. How accurate is the GPS on the iPhone 4? I ask because I'm working on an enterprise project for a company, and part 2 of it will deal with iDevice development where I have to determine the position of the user. I'd like to know if the GPS is accurate enough to sense the user moving within rooms because the user will have to "tag" sections of the room as they move about it.

Thanks in advance!

P.S. Pressuming that it won't make much of a difference, but the users will actually end up using the iPads, not iPhones, and more than likely the iPad 2 will be out by the time the entire project is completed. I don't know if the iPad 2 will have a better GPS receiver or not, but at the minimum I should use the iPad/iPhone 4 GPS receiver...

Answer 1

Most buildings will not allow reception of an accurate set of GPS signals (if they can be received at all) indoors. The roof/ceiling/floors above are just too thick. Even a lot of trees overhanging a building will degrade the signal from the GPS satellites.

You might have a chance if all the rooms have very large unobstructed windows with no overhangs, and it's the right time of day for several satellites to be in view out that window.

Outdoors, in the clear, the iPhone 4 GPS seems to be very accurate. Sometimes I can walk around my parked car, and see the blue dot in the Maps app follow me in a circle.

Answer 2

I have done some work with a large location data set. My result set is based on cars driving outside and will therefore be, on average, more accurate than those taken inside (based on line of sight to satellites).

For the 650,704 location updates I used in my tests, I found the average accuracy radius was 246m (91m if your remove >1km outliers). 85.1% of updates had an accuracy of less than 100m. So given that your update will not be as accurate as these, I don't imagine you will have much success tracking indoor location changes.

For a further description of my results.

Answer 3

It is very difficult, and most of the time impossible to obtain a GPS signal inside a building. The type of waves used by the GPS (radio waves) are not powerful enough to go through the structure itself.

A simpler and probably cheaper solution would be to give people maybe tags or cards and install some sort of trnasreceiver in each room.

Answer 4

It seems the original question was "how accurate is the GPS on an iPhone 4", which hasn't exactly been answered yet.

I've done lots of testing with the accuracy of the GPS chips in iPhone 4, iPhone 4s, and iPhone 5, and the most accurate reading allowed seems to be ~5 meters, or ~16 feet when you're outside with clear line of sight to the sky. I'm guessing this is a software limitation imposed by Apple to conserve battery.