android - 在多边形上找到离用户位置最近的点

Question

我有一个应用可以找到我的用户与多边形之间的最短距离。

我想将多边形转换为地理围栏以检查用户与区域之间的距离，以便为用户提供更准确的信息。

我该怎么做？

这是 MapsActivity

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, LocationListener, MinimumDistanceTask.GetMinimumDistanceListener {
    private GoogleMap mMap;
    private  LocationManager manager;
    private double lat, lng;
    private KmlLayer layer;
    private LatLng latLngTest;
    private  boolean contains = false;
    private  ArrayList<LatLng> outerBoundary;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
        manager = (LocationManager) getSystemService(LOCATION_SERVICE);
    }

    @Override
    protected void onResume() {
        super.onResume();
        String provider = LocationManager.GPS_PROVIDER;

        //take the user location every second
        try {
            manager.requestLocationUpdates(provider, 1000, 0, this);
        }catch (SecurityException e){

        }
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
    }

    @Override
    public void onLocationChanged(Location location) {
        //clear map before create new location
        mMap.clear();
        try {
            //load the kml file
            layer = new KmlLayer(mMap, R.raw.polygon_layer, this);
            layer.addLayerToMap();

        } catch (IOException e) {
            e.printStackTrace();
        } catch (XmlPullParserException e) {
            e.printStackTrace();
        }

        lat = location.getLatitude();
        lng = location.getLongitude();
        latLngTest = new LatLng(lat,lng);
        // Add a marker in user location
        LatLng userLocation = new LatLng(latLngTest.latitude, latLngTest.longitude);
        mMap.addMarker(new MarkerOptions().position(userLocation).title("you are here"));
        mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(userLocation, 15));

        //check if the user in the polygon
        boolean inside = ifUserInside();

        if(inside){
            Toast.makeText(MapsActivity.this, "you are in the polygon", Toast.LENGTH_SHORT).show();
        }else{
            Toast.makeText(MapsActivity.this, "you are outside the polygon", Toast.LENGTH_SHORT).show();
            //create the string address for the url
            String address = "";
            for (int i = 0; i < outerBoundary.size(); i++) {
                address += (outerBoundary.get(i).toString() + "|");
                address = address.replace("lat/lng:", "");
                address = address.replace(" ", "");
                address = address.replace("(", "");
                address = address.replace(")", "");
            }
            MinimumDistanceTask task = new MinimumDistanceTask(this);
            task.execute("https://maps.googleapis.com/maps/api/distancematrix/json?units=imperial&origins="+latLngTest.latitude+ "," + latLngTest.longitude
                    + "&destinations=" + address + "&mode=walking");
        }

    }

    @Override
    public void getMinimumDistance(int closeLocation) {
        //check if you get results properly
        if(closeLocation != -1) {
            GetDirection direction = new GetDirection();
            direction.execute("https://maps.googleapis.com/maps/api/directions/json?origin=" + latLngTest.latitude + "," + latLngTest.longitude
                    + "&destination=" + outerBoundary.get(closeLocation).latitude + "+" + outerBoundary.get(closeLocation).longitude);
        }
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }

    public boolean ifUserInside(){
        if (layer.getContainers() != null) {
            for (KmlContainer container : layer.getContainers()) {
                if (container.getPlacemarks() != null) {
                    for (KmlPlacemark placemark : container.getPlacemarks()) {
                        contains = false;

                        if (placemark.getGeometry() instanceof KmlPolygon) {
                            KmlPolygon polygon = (KmlPolygon) placemark.getGeometry();

                            // Get the outer boundary and check if the test location lies inside
                            outerBoundary = polygon.getOuterBoundaryCoordinates();
                            contains = PolyUtil.containsLocation(latLngTest, outerBoundary, true);



                            if (contains) {
                                // Get the inner boundaries and check if the test location lies inside
                                ArrayList<ArrayList<LatLng>> innerBoundaries = polygon.getInnerBoundaryCoordinates();
                                if (innerBoundaries != null) {
                                    for (ArrayList<LatLng> innerBoundary : innerBoundaries) {
                                        // If the test location lies in a hole, the polygon doesn't contain the location
                                        if (PolyUtil.containsLocation(latLngTest, innerBoundary, true)) {
                                            contains = false;

                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        return contains;
    }

    public class GetDirection extends AsyncTask<String , Void, String> {
        HttpsURLConnection connection = null;
        BufferedReader reader = null;
        StringBuilder builder = new StringBuilder();
        @Override
        protected String doInBackground(String... params) {
            String address = params[0];

            try {
                URL url = new URL(address);
                connection = (HttpsURLConnection) url.openConnection();
                if(connection.getResponseCode() != HttpURLConnection.HTTP_OK){
                    return "Error from server";
                }

                reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String line;
                while ((line = reader.readLine()) != null){
                    builder.append(line);
                }

            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return builder.toString();
        }

        @Override
        protected void onPostExecute(String s) {
        //get the polyline string
            String polygonPoints = "";

            try {
                JSONObject object = new JSONObject(s);
                JSONArray array = object.getJSONArray("routes");
                for (int i = 0; i < array.length(); i++) {
                    JSONObject arrObj1 = array.getJSONObject(i);
                    JSONObject points = arrObj1.getJSONObject("overview_polyline");
                    polygonPoints = points.getString("points");

                }
                //convert the string to polyline;
                ArrayList<LatLng> a = new ArrayList<>(decodePolyPoints(polygonPoints));
                //add polyline to the map
                mMap.addPolyline(new PolylineOptions().addAll(a).width(10).color(Color.BLUE));

            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }

    //the method that convert the string to polyline
    public static ArrayList<LatLng> decodePolyPoints(String encodedPath){
        int len = encodedPath.length();

        final ArrayList<LatLng> path = new ArrayList<LatLng>();
        int index = 0;
        int lat = 0;
        int lng = 0;

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

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

            path.add(new LatLng(lat * 1e-5, lng * 1e-5));
        }

        return path;
    }
}

这是我获取最小距离点的AsyncTask

public class MinimumDistanceTask extends AsyncTask<String, Void, Integer>{

    private int closeLocation;
    // private String points;
    private GetMinimumDistanceListener listener;

    public MinimumDistanceTask(GetMinimumDistanceListener listener){
        // this.points = points;
        this.listener = listener;
    }

    @Override
    protected Integer doInBackground(String... params) {
        HttpsURLConnection connection = null;
        BufferedReader reader = null;
        StringBuilder builder = new StringBuilder();
        int minimumDis = -1;

            String address = params[0];

            try {
                URL url = new URL(address);
                connection = (HttpsURLConnection) url.openConnection();
                if(connection.getResponseCode() != HttpURLConnection.HTTP_OK){
                    return -1;
                }

                reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String line;
                while ((line = reader.readLine()) != null){
                    builder.append(line);
                }
            ///get the json data
                JSONObject jsonObject1 = new JSONObject(builder.toString());
                JSONArray points = jsonObject1.getJSONArray("rows");
                JSONObject jsonObject2 = points.getJSONObject(0);
                JSONArray elements = jsonObject2.getJSONArray("elements");
                for (int i = 0; i < elements.length(); i++) {
                    JSONObject jsonObject3 = elements.getJSONObject(i);
                    JSONObject distance = jsonObject3.getJSONObject("distance");
                    if( distance.getInt("value") < minimumDis || minimumDis == -1) {
                        minimumDis = distance.getInt("value");
                        closeLocation = i;
                    }
                }

            } catch (MalformedURLException | JSONException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

        return closeLocation;
        }

    @Override
    protected void onPostExecute(Integer closeLocation) {
            listener.getMinimumDistance(closeLocation);

    }

    public interface GetMinimumDistanceListener{
        void getMinimumDistance(int closeLocation);
    }
}

非常感谢:)

Answer 1

您可以使用如下函数来计算距离由 List<LatLng> 定义的多边形最近的点。和给定的 LatLng .

它使用 PolyUtil.distanceToLine来自 Google Maps Android API Utility Library计算测试之间的距离 LatLng和列表的每一段，以及一个基于 distanceToLine 的方法方法来自 https://github.com/googlemaps/android-maps-utils/blob/master/library/src/com/google/maps/android/PolyUtil.java计算点在线段上的投影。

private LatLng findNearestPoint(LatLng test, List<LatLng> target) {
    double distance = -1;
    LatLng minimumDistancePoint = test;

    if (test == null || target == null) {
        return minimumDistancePoint;
    }

    for (int i = 0; i < target.size(); i++) {
        LatLng point = target.get(i);

        int segmentPoint = i + 1;
        if (segmentPoint >= target.size()) {
            segmentPoint = 0;
        }

        double currentDistance = PolyUtil.distanceToLine(test, point, target.get(segmentPoint));
        if (distance == -1 || currentDistance < distance) {
            distance = currentDistance;
            minimumDistancePoint = findNearestPoint(test, point, target.get(segmentPoint));
        }
    }

    return minimumDistancePoint;
}

/**
 * Based on `distanceToLine` method from
 * https://github.com/googlemaps/android-maps-utils/blob/master/library/src/com/google/maps/android/PolyUtil.java
 */
private LatLng findNearestPoint(final LatLng p, final LatLng start, final LatLng end) {
    if (start.equals(end)) {
        return start;
    }

    final double s0lat = Math.toRadians(p.latitude);
    final double s0lng = Math.toRadians(p.longitude);
    final double s1lat = Math.toRadians(start.latitude);
    final double s1lng = Math.toRadians(start.longitude);
    final double s2lat = Math.toRadians(end.latitude);
    final double s2lng = Math.toRadians(end.longitude);

    double s2s1lat = s2lat - s1lat;
    double s2s1lng = s2lng - s1lng;
    final double u = ((s0lat - s1lat) * s2s1lat + (s0lng - s1lng) * s2s1lng)
            / (s2s1lat * s2s1lat + s2s1lng * s2s1lng);
    if (u <= 0) {
        return start;
    }
    if (u >= 1) {
        return end;
    }

    return new LatLng(start.latitude + (u * (end.latitude - start.latitude)),
            start.longitude + (u * (end.longitude - start.longitude)));


}

您可以使用以下代码进行测试:

List<LatLng> points = new ArrayList<>();
points.add(new LatLng(2, 2));
points.add(new LatLng(4, 2));
points.add(new LatLng(4, 4));
points.add(new LatLng(2, 4));
points.add(new LatLng(2, 2));

LatLng testPoint = new LatLng(3, 0);

LatLng nearestPoint = findNearestPoint(testPoint, points);
Log.e("NEAREST POINT: ", "" + nearestPoint); // lat/lng: (3.0,2.0)
Log.e("DISTANCE: ", "" + SphericalUtil.computeDistanceBetween(testPoint, nearestPoint)); // 222085.35856591124