Convert Polyline to Route

Question

I've got an app that tracks vehicles and draws a polyline of their travel path on a map. I want to convert this polyline into a route using the directions service routing. This will allow me to be able to drag the path around and manipulate it etc.

The problem is I can't think of a nice solution to this, and I'm not sure if it's possible. If I pass in the array of coordinates of the polyline to the directions service route it only draws a route using the start and the end of the polyline, it doesn't take into consideration any of the coordinates in between.

I tried to generate a 'waypoints' array using the polyline coordinates array by evenly dividing it and getting 8 coordinates in between and passing those in as the waypoints but it fails to render at all now. If I test the code using a coordinates array that was generated by drawing a route it works though, so I know the code is working. I'm presuming it fails because some of these coordinates may be slightly off the road (it's a polyline drawn from GPS positioning, so it's not 100% accurate), and Google doesn't just snap it to the nearest accepted location.

Can anyone think of a solution to this?

Here's code examples to make it a bit clearer:

// In the polyline app
var encoded_path = google.maps.geometry.encoding.encodePath(coordinate_array)



// In the route app
var coordinates = google.maps.geometry.encoding.decodePath(encoded_path);

var waypoints = [];

// Evenly get coordinates across the entire array to be used as waypoints
for (var i = 1; i <= 8; ++i) {
   var index = Math.floor((coordinates.length/10) * i);

   if (index >= coordinates.length - 1)
      break;

   waypoints.push({
      'location': new google.maps.LatLng(coordinates[index].lat(), coordinates[index].lng()),
      'stopover': false
   });
}

var request = {
   origin: coordinates[0],
   destination: coordinates[coordinates.length - 1],
   travelMode: google.maps.DirectionsTravelMode.DRIVING,
   waypoints: waypoints
};

MapService.directionsService.route(request, function(response, status) {
   if (status == google.maps.DirectionsStatus.OK) {
      MapService.directionsDisplay.setDirections(response);
   }
});

Answer 1

It's been a while and there's a better answer now, the Roads API: https://developers.google.com/maps/documentation/roads/intro

Directions API is not intended for this use case, there are several good reasons to not even try:

• Waypoints that are stop-over (default) will allow any direction of travel, in or out, when snapping to the nearest road, regardless of previous/next waypoints.

• Waypoints that are not stop-over (via:) will be very strict when snapping to roads, typical GPS offset will throw it off and cause ZERO_RESULTS (no route)-

• Even if all waypoints work out well, the route will be the best route for a generic driver, not necessarily the route followed by the vehicle that sampled the positions used as waypoints.

• If a vehicle samples a position at the intersection of 2 roads at different altitudes (elevated pass, bridge, tunnel, etc.), if the GPS offset makes the point be in the wrong road, it can throw routing wildly off.