Is there a way to know which direction one iPhone is from another?

Question

Presume I have two+ iPhones connected to the same server. Using the sensors built in the iPhone and any possible calculations based on their information, is there any way to tell which direction one phone is from another?

They would be in the same room, so the fluctuation of GPS would not work very well here.

I've tried to model two points on a graph using only their compass readings, but I do not think this will work alone. I could be wrong though.

Answer 1

You could setup a calibration phase in your program where you start each phone in an exact position, and then using the 6 axis motion continually calculate the exact current position (in all 6 axis). But the longer you run that calculation the further from true position you will be and eventually (given a long enough time) one phone could think it's in canada and the other in Mexico.

So It could work for short term spurts if you do a calibration every time you want to start.

There is also the possibility of bluetooth localization, but that would require at least 3 phones and the sharing of positional data between them. Or you could do wifi location, but that would require the same as the bluetooth.

Long story short if you want inches localization it's not going to happen. If you want yards localization it's possible, but not as usable.

Answer 2

As you already mentioned, GPS does not work very well when used inside buildings. Thus, it is not possible to get the direction, as you don't have two reliable positions.

Indoor localisation should be much easier with iOS7 and location beacons .. but this does not help much now.