Measuring distance between two iOS Devices

Question

Yeah, I'm currently wondering about this. In my use case the devices will be 50cm to 10m apart and I'd like it to be accurate to at least 10 cm. (Therefore GPS is not an option)

2 Ways spring to mind:

Sound: I asked about this in the dev forums and I'm in contact with laanlabs, about the code of their sonar ruler.

Picture on one device + Camera on the other: Seems easier to set up, since my user case involves the user facing one device at 90 degrees anyway. But it would be more work for the user to face the camero into the direction and it would not react to a change in distance.

Now the question: Is anyone aware of any code that does something like this already? Possibly a non-iPhone general c-Project?

Answer 1

Method with camera: we already know size for each device. You take a picture of device, calculate it's height/width to determine type of device (iPhone/iPod or iPad), than calculate a distance.

For example - if device is iPhone you know, that its size is 115x58 mm. On picture it NxM pixels. Now you can calculate the distance. (If N & M smaller hence distance is larger)

Answer 2

If you were to use the sound method one approach would be to have device A emit a sound, device B would then be listening for this at all times and on detection echo back a secondary sound. This would give you a round-trip time from which you could calculate distance - don't forget to compensate for latency between detection re-emission as well.

Answer 3

I am not sure about but this is what i found from one of the answers in this previous SO question How to measure distance between two iphone devices using bluetooth?

Using bluetooth for localization is a very well known research field . The short answer is: you can't. Signal strength isn't a good indicator of distance between two connected bluetooth devices, because it is too much subject to environment condition (is there a person between the devices? How is the owner holding his/her device? Is there a wall? Are there any RF reflecting surfaces?). Using bluetooth you can at best obtain a distance resolution of few meters, but you can't calculate the direction, not even roughly.

You may obtain better results by using multiple bluetooth devices and triangulating the various signal strength, but even in this case it's hard to be more accurate than few meters in your estimates.