Convert Polyline to Route - google-maps

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

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.

Answer 3

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);
}
}
}