Android谷歌地图绘制两点之间的路径

Question

我想在两点之间绘制一条路径并计算从A移动到B需要多长时间.我认为Google Maps API是一项微不足道的任务.

我找到的所有内容PolyUtil都是文档中的小片段,而不是如何使用它.

我做了什么 ？

MapsActivity在onMapReady方法内部我正在尝试创建一个编码路径:

List<LatLng> latLngList = new ArrayList<>();
latLngList.add(new LatLng(56.952503, 24.083719));
latLngList.add(new LatLng(55.877526, 26.533898));

String encodedPath = PolyUtil.encode(latLngList);

但下一步是什么？如何在地图上绘制此路径？如何计算这点之间的车/步行距离？

Answer 1

路径是点的序列.其中一个解决方案是向Google maps API发出HTTP请求,将两个位置指定为参数,然后返回JSON,描述在两点之间建立路径所需的点.要求执行此操作的代码如下所示:

1. 获取路线网址需要调用Google Maps API

private String  getMapsApiDirectionsUrl(LatLng origin,LatLng dest) {
   // Origin of route
 String str_origin = "origin="+origin.latitude+","+origin.longitude;

 // Destination of route
 String str_dest = "destination="+dest.latitude+","+dest.longitude;        


 // Sensor enabled
 String sensor = "sensor=false";            

 // Building the parameters to the web service
 String parameters = str_origin+"&"+str_dest+"&"+sensor;

 // Output format
 String output = "json";

 // Building the url to the web service
 String url = "https://maps.googleapis.com/maps/api/directions/"+output+"?"+parameters;


 return url;

}

2. 在后台进行URL调用

   private class ReadTask extends AsyncTask<String, Void , String> {
   
   @Override
   protected String doInBackground(String... url) {
       // TODO Auto-generated method stub
       String data = "";
       try {
           MapHttpConnection http = new MapHttpConnection();
           data = http.readUr(url[0]);
   
   
       } catch (Exception e) {
           // TODO: handle exception
           Log.d("Background Task", e.toString());
       }
       return data;
   }
   
   @Override
   protected void onPostExecute(String result) {
       super.onPostExecute(result);
       new ParserTask().execute(result);
   }
   
   }
   

  public class MapHttpConnection {
  public String readUr(String mapsApiDirectionsUrl) throws IOException{
      String data = "";
      InputStream istream = null;
      HttpURLConnection urlConnection = null;
      try {
          URL url = new URL(mapsApiDirectionsUrl);
          urlConnection = (HttpURLConnection) url.openConnection();
          urlConnection.connect();
          istream = urlConnection.getInputStream();
          BufferedReader br = new BufferedReader(new InputStreamReader(istream));
          StringBuffer sb = new StringBuffer();
          String line ="";
          while ((line = br.readLine()) != null) {
              sb.append(line);
          }
          data = sb.toString();
          br.close();


      }
      catch (Exception e) {
          Log.d("Exception while reading url", e.toString());
      } finally {
          istream.close();
          urlConnection.disconnect();
      }
      return data;

  }
}

3. 创建Parser类以将数据从JSON解析为指针列表

   public class PathJSONParser {
   
   public List<List<HashMap<String, String>>> parse(JSONObject jObject) {
       List<List<HashMap<String, String>>> routes = new ArrayList<List<HashMap<String,String>>>();
       JSONArray jRoutes = null;
       JSONArray jLegs = null;
       JSONArray jSteps = null;
       try {
           jRoutes = jObject.getJSONArray("routes");
           for (int i=0 ; i < jRoutes.length() ; i ++) {
               jLegs = ((JSONObject) jRoutes.get(i)).getJSONArray("legs");
               List<HashMap<String, String>> path = new ArrayList<HashMap<String,String>>();
               for(int j = 0 ; j < jLegs.length() ; j++) {
                   jSteps = ((JSONObject) jLegs.get(j)).getJSONArray("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);
                       for(int l = 0 ; l < list.size() ; l ++){
                           HashMap<String, String> hm = new HashMap<String, String>();
                           hm.put("lat",
                                   Double.toString(((LatLng) list.get(l)).latitude));
                           hm.put("lng",
                                   Double.toString(((LatLng) list.get(l)).longitude));
                           path.add(hm);
                       }
                   }
                   routes.add(path);
               }
   
           }
   
       } catch (Exception e) {
           e.printStackTrace();
       }
       return routes;
   
   }
   
   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;
   }}
   

4. 使用另一个线程 进行解析以扩展性能

private class ParserTask extends AsyncTask<String,Integer, List<List<HashMap<String , String >>>> {
  @Override
  protected List<List<HashMap<String, String>>> doInBackground(
          String... jsonData) {
      // TODO Auto-generated method stub
      JSONObject jObject;
      List<List<HashMap<String, String>>> routes = null;
      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) {
      ArrayList<LatLng> points = null;
      PolylineOptions polyLineOptions = null;

      // traversing through routes
      for (int i = 0; i < routes.size(); i++) {
          points = new ArrayList<LatLng>();
          polyLineOptions = new PolylineOptions();
          List<HashMap<String, String>> path = routes.get(i);

          for (int j = 0; j < path.size(); j++) {
              HashMap<String, String> point = path.get(j);

              double lat = Double.parseDouble(point.get("lat"));
              double lng = Double.parseDouble(point.get("lng"));
              LatLng position = new LatLng(lat, lng);

              points.add(position);
          }

          polyLineOptions.addAll(points);
          polyLineOptions.width(4);
          polyLineOptions.color(Color.BLUE);
      }

      googleMap.addPolyline(polyLineOptions);

  }}

4. 当你想获得两点的路径时

 String url = getMapsApiDirectionsUrl(latlngOne, latlngTwo);                    
    ReadTask downloadTask = new ReadTask();       
    // Start downloading json data from Google Directions API
    downloadTask.execute(url);

计算点之间的距离

float[] results = new float[1];
Location.distanceBetween(latLongA.latitude, latLongB.longitude,
                         latLongB.latitude, latLongB.longitude,
                         results); 

结果将以米为单位