title: Checking for Deviation from Google Maps Route
body: <p>I am doing a project for school involving maps and navigation. What I have done till now is to  just use the Google Directions Web API to retrieve a JSON output and then parse it to get my directions. 
  When navigating, a user may deviate from the path and here is where I want to do some rerouting. I think this might be a bit vague, but, how can I check for deviation from a certain route?  </p>