GPS on iOS, how accurate between separate phones?

Question

Can anyone help me with some research? I am wondering if the built in GPS capabilities are accurate enough to tell users apart in terms of direction. I know they are accurate enough to place you within a 5 foot radius of where you are but not pinpoint exactly, but if 5 people are standing next to each other, can it tell who is in front of who? and who is behind who? Who is to the left? Who is to the right? If not, is this possible with Bluetooth or NFC? Help is much appreciated. Thanks

Answer 1

In my experience you're doing well if you get a GPS reading from an iPhone accurate within 20 feet. You're dreaming if you think you can get 5 foot accuracy, and no, you cannot use such inaccurate data to figure out relative positioning of people standing right next to each other.

BLE is purely signal strength, so even non-directional distance readings aren't that reliable beyond far/medium/near/immediate area type readings. (Signal strength is affected by how you hold the phone, whether your body is partly blocking the path to the other device, the radio-reflectivity of nearby objects, and lots of other factors.) There's no directional information, so you won't be able to figure out relative positioning there either. I've seen "trilateration" that attempts to measure signal strength from multiple beacons at known locations, but due to the inaccuracy of the signal measurements it's dreadfully inaccurate.

NFC is only for devices that are almost touching.

Unless you attach some sort of external hardware device that does close range position calculations I think you are out of luck.

Answer 2

GPS technology is inherently innacurate and the innacuracy is multiplied by 2 whenever you want to compare a position with a previously recorded position. To answer your question: No with GPS technology alone you will not be able to achieve such precision.