Question

In my iPhone app I’m using MapKit to show the user where he is, i also want to show him the total time and duration
to his destination.
Can i use Google direction API to do that?
What I’m planning to do is to ask for direction every few seconds (up to 2500 requests i know..)
and only show the “direction” and “duration” values from the response to the user.

Answer 1

Yes you can.

The JSON response includes distance and duration, e.g.

"duration": {
    "value": 74384,
    "text": "20 hours 40 mins"
},
"distance": {
    "value": 2137146,
    "text": "1,328 mi"
},

I would suggest only calling the API every minute or so. You can use linear interpolation to work out the in-between values (your will have to estimate the speed to decrease distance by the right amount).

To implement this….

1. Frist save the time when the result is returned.

   self.responseTime = [NSDate date];

2. Calculate the speed that google used.

   Speed = Distance / Time

   So in the example the raw units are meters and seconds so

   Speed = 2137146 / 74384 = 28.7... ms^1

3. Use NSTimer to get a recurring callback every so often. In the callback you need:

   1. Decrease time by the elapsed time since the response time.

   2. Decease the distance by the calculated speed * elapsed time since the response time.

   3. Update the labels.