How to buffer a polyline in Android or draw a polygon around a polyline?

Question

I am trying to put a buffer around a polyline in MapsV2 for android but I haven't find how to do it yet, I was thinking on drawing a polygon around the polyline but also haven't found anyone that have done that, is it possible?

Answer 1

in Google's directions api (https://maps.googleapis.com/maps/api/directions/json?origin=75+9th+Ave+New+York,+NY&destination=MetLife+Stadium+1+MetLife+Stadium+Dr+East+Rutherford,+NJ+07073&key=YOUR_API_KEY ) you get one overview_polyline jsonObject, get encoded points From here, and decode it using this method:

private List<LatLng> decodePoly(String encoded) {

        List<LatLng> poly = new ArrayList<>();
        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;
    }

You get List of latitude and longitude, now, using google map's getMapAsync Method add this latlng in your map :

googleMap.addPolyline(new PolylineOptions().geodesic(true).addAll(latLngList));

Answer 2

Do you want to draw Path on the map or Do you want to draw straight lines on the map.

In both cases you can follow below code

PolylineOptions polyLineOptions = new PolylineOptions();
ArrayList<LatLng> points = new ArrayList<>();

//Code to populate Latlng

polyLineOptions.addAll(points);
polyLineOptions.width(mActivity.getResources().getDimensionPixelSize(R.dimen._2sdp));
polyLineOptions.color(ContextCompat.getColor(mContext, Color_Resource_id));
if (polyLineOptions != null) {
    googleMap.addPolyline(polyLineOptions);
}

Above code is to draw only straight lines on Map.

Now if you wanna draw complete path on Map, You would probably need to use google direction api https://maps.googleapis.com/maps/api/directions/

You can use below class to parse response from the same to get total latlngs

public class PathJSONParser {

    public List<List<HashMap<String, String>>> parse(JSONObject jObject) {
        List<List<HashMap<String, String>>> routes = new ArrayList<>();
        JSONArray jRoutes;
        JSONArray jLegs;
        JSONArray jSteps;
        try {
            jRoutes = jObject.getJSONArray("routes");
            /** Traversing all routes */
            for (int i = 0; i < jRoutes.length(); i++) {
                jLegs = ((JSONObject) jRoutes.get(i)).getJSONArray("legs");
                List<HashMap<String, String>> path = new ArrayList<>();

                /** Traversing all legs */
                for (int j = 0; j < jLegs.length(); j++) {
                    jSteps = ((JSONObject) jLegs.get(j)).getJSONArray("steps");

                    /** Traversing all steps */
                    for (int k = 0; k < jSteps.length(); k++) {
                        String polyline;
                        polyline = (String) ((JSONObject) ((JSONObject) jSteps
                                .get(k)).get("polyline")).get("points");
                        List<LatLng> list = decodePoly(polyline);

                        /** Traversing all points */
                        for (int l = 0; l < list.size(); l++) {
                            HashMap<String, String> hm = new HashMap<>();
                            hm.put("lat",
                                    Double.toString(( list.get(l)).latitude));
                            hm.put("lng",
                                    Double.toString(( list.get(l)).longitude));
                            path.add(hm);
                        }
                    }
                    routes.add(path);
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
        return routes;
    }

    /**
     * Method Courtesy :
     * jeffreysambells.com/2010/05/27
     * /decoding-polylines-from-google-maps-direction-api-with-java
     * */
    private List<LatLng> decodePoly(String encoded) {

        List<LatLng> poly = new ArrayList<>();
        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;
    }
}

And finally you can use this in your class with below code

private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String, String>>>> {

        @Override
        protected List<List<HashMap<String, String>>> doInBackground(String... jsonData) {

            JSONObject jObject;
            List<List<HashMap<String, String>>> routes = new ArrayList<>();

            try {
                jObject = new JSONObject(jsonData[0]);
                PathJSONParser parser = new PathJSONParser();
                routes = parser.parse(jObject);
            } catch (Exception e) {
                e.printStackTrace();
            }

            return routes;
        }

        @Override
        protected void onPostExecute(List<List<HashMap<String, String>>> routes) {
            if (routes != null && routes.size() > 0) {
                new DrawPoly().execute(routes);
            }

        }
    }

    private class DrawPoly extends AsyncTask<List<List<HashMap<String, String>>>,
            PolylineOptions, PolylineOptions> {

        @Override
        protected PolylineOptions doInBackground(List<List<HashMap<String, String>>>... params) {
            PolylineOptions polyLineOptions = new PolylineOptions();
            ArrayList<LatLng> points;

            if (params[0] != null && params[0].size() > 0) {
                // traversing through routes
                for (int j = 0; j < params[0].size(); j++) {
                    points = new ArrayList<>();
                    polyLineOptions = new PolylineOptions();
                    try {
                        List<HashMap<String, String>> path = params[0].get(j);
                        for (int k = 0; k < path.size(); k++) {
                            HashMap<String, String> point = path.get(k);
                            double lat = Double.parseDouble(point.get("lat"));
                            double lng = Double.parseDouble(point.get("lng"));
                            LatLng position = new LatLng(lat, lng);
                            points.add(position);
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    polyLineOptions.addAll(points);
                    polyLineOptions.width(mActivity.getResources().getDimensionPixelSize(R.dimen.five));
                    polyLineOptions.color(ContextCompat.getColor(mContext, R.color.red));
                }
            }
            return polyLineOptions;
        }

        @Override
        protected void onPostExecute(PolylineOptions polyLineOptions) {
            super.onPostExecute(polyLineOptions);
            if (polyLineOptions != null) {
                googleMap.addPolyline(polyLineOptions);
            }
        }
    }

You need to make sure you are putting it in asyncTask. I hope it will work for you.