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.

Answer 2

public String makeURL (double sourcelat, double sourcelog, double destlat, double destlog ){
    StringBuilder urlString = new StringBuilder();
    urlString.append("http://maps.googleapis.com/maps/api/directions/json");
    urlString.append("?origin=");// from
    urlString.append(Double.toString(sourcelat));
    urlString.append(",");
    urlString
            .append(Double.toString( sourcelog));
    urlString.append("&destination=");// to
    urlString
            .append(Double.toString( destlat));
    urlString.append(",");
    urlString.append(Double.toString( destlog));
    urlString.append("&sensor=false&mode=driving");
    return urlString.toString();

}

private List<LatLng> decodePoly(String encoded) {

    List<LatLng> poly = new ArrayList<LatLng>();
    int index = 0, len = encoded.length();
    int lat = 0, lng = 0;

    while (index < len) {
        int b, shift = 0, result = 0;
        do {
            b = encoded.charAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlat = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lat += dlat;

        shift = 0;
        result = 0;
        do {
            b = encoded.charAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlng = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lng += dlng;

        LatLng p = new LatLng( (((double) lat / 1E5)),
                 (((double) lng / 1E5) ));
        poly.add(p);
    }

    return poly;
}


public class JSONParser {

    InputStream is = null;
    JSONObject jObj = null;
    String json = "";
    // constructor
    public JSONParser() {
    }
    public String getJSONFromUrl(String url) {

        // Making HTTP request
        try {
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();           

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }

            json = sb.toString();
            is.close();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }
        return json;

    }
}

public void drawPath(String  result) {

    try {
            //Tranform the string into a json object
           final JSONObject json = new JSONObject(result);
           JSONArray routeArray = json.getJSONArray("routes");
           JSONObject routes = routeArray.getJSONObject(0);
           JSONObject overviewPolylines = routes.getJSONObject("overview_polyline");
           String encodedString = overviewPolylines.getString("points");
           List<LatLng> list = decodePoly(encodedString);

           for(int z = 0; z<list.size()-1;z++){
                LatLng src= list.get(z);
                LatLng dest= list.get(z+1);
                theMap.addPolyline(new PolylineOptions()
                .add(src,dest)
                .width(2)
                .color(Color.BLUE).geodesic(true));
            }

    } 
    catch (JSONException e) {

    }
} 


private class connectAsyncTask extends AsyncTask<Void, Void, String>{
        private ProgressDialog progressDialog;
        String url;
        connectAsyncTask(String urlPass){
            url = urlPass;

        }
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            progressDialog = new ProgressDialog(YOUR_Activity.this);
            progressDialog.setMessage("Fetching route, Please wait...");
            progressDialog.setIndeterminate(true);
            progressDialog.show();
        }
        @Override
        protected String doInBackground(Void... params) {
            JSONParser jParser = new JSONParser();
            String json = jParser.getJSONFromUrl(url);
            return json;
        }
        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);   
            progressDialog.hide();        
            if(result!=null){
                drawPath(result);
            }
        }
    }

Answer 3

You can use the direction api to check the waypoints when it ends at a road: Map of all points below a certain time of travel?. Then delete the others to create a route from the entire polyline.