The mention of elevation data got me thinking. Can the GPS chip in an iPhone return 3-space data (that is, altitude) or is it only capable of returning ground-based coordinates? Simple math shows that it requires a minimum of three satellite fixes (and I think good GPS chips usually try to use four or more, in the name of error correction) to uniquely identify a single ground-based coordinate (three intersecting circles.) It requires a minimum of four satellites (preferably five or more) to identify a single 3-space coordinate (four intersecting spheres.)
If the chip in an iPhone can lock on to 4-5 satellites at once, then it can return 3-space coordinates (although an iOS firmware update may also be required in order to get those coordinates into apps.) Such a thing would be great for devices like AirDog, since they could then track you as your altitude changes (e.g. parasailing) in addition to tracking your position over the ground.
Sure it can, the iPhone already has this info, I believe from a barometer:
Though I would presume it already knows the distantce to the user from the BT signal to that thingy you'll need to wear:
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Sure it can, the iPhone already has this info, I believe from a barometer:
Though I would presume it already knows the distantce to the user from the BT signal to that thingy you'll need to wear: