Is there a way to have a Map Kit map recalculate directions if the user's current location diverges from the route steps? I don't see anything in the MKDirections documentation or Map Kit functions reference that's ready-made for that.
If I have to roll my own, I'm not sure where to start. Perhaps by seeing if the user's current location diverges by a certain amount from the polyline of the current route step, although based on my scant knowledge, I wonder if some Core Location conversions would have to take place.