Question

我有一个数组列表，ArrayList（），用于保存lat和lng。我想在这个数组中得到元素，以便计算距离。

private void whereAmI(){

    Location location = manager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
    updateWithNewLocation(location);

    //GPS Listener
    manager.addGpsStatusListener(gpsListener);

    //Location Listener
    int minTime = 0;//ms
    int minDist = 0;//meter
    manager.requestLocationUpdates(LocationManager.GPS_PROVIDER, minTime, minDist, locationListener);
}

GpsStatus.Listener gpsListener = new GpsStatus.Listener() {
    @Override
    public void onGpsStatusChanged(int event) {
        switch (event) {
            case GpsStatus.GPS_EVENT_STARTED:
                Log.d("x=", "GPS_EVENT_STARTED");
                Toast.makeText(MapsActivity.this, "GPS_EVENT_STARTED", Toast.LENGTH_SHORT).show();
                break;
            case GpsStatus.GPS_EVENT_STOPPED:
                Log.d("x=", "GPS_EVENT_STOPPED");
                Toast.makeText(MapsActivity.this, "GPS_EVENT_STOPPED", Toast.LENGTH_SHORT).show();
                break;
            case GpsStatus.GPS_EVENT_FIRST_FIX:
                Log.d("x=", "GPS_EVENT_FIRST_FIX");
                Toast.makeText(MapsActivity.this, "GPS_EVENT_FIRST_FIX", Toast.LENGTH_SHORT).show();
                break;
            case GpsStatus.GPS_EVENT_SATELLITE_STATUS:
                Log.d("x=", "GPS_EVENT_SATELLITE_STATUS");
                break;
        }
    }
};

LocationListener locationListener = new LocationListener(){
    @Override
    public void onLocationChanged(Location location) {
        updateWithNewLocation(location);
    }

    @Override
    public void onProviderDisabled(String provider) {
        updateWithNewLocation(null);
    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        switch (status) {
            case LocationProvider.OUT_OF_SERVICE:
                Log.v("x=", "Status Changed: Out of Service");
                Toast.makeText(MapsActivity.this, "Status Changed: Out of Service", Toast.LENGTH_SHORT).show();
                break;
            case LocationProvider.TEMPORARILY_UNAVAILABLE:
                Log.v("x=", "Status Changed: Temporarily Unavailable");
                Toast.makeText(MapsActivity.this, "Status Changed: Temporarily Unavailable", Toast.LENGTH_SHORT).show();
                break;
            case LocationProvider.AVAILABLE:
                Log.v("x=", "Status Changed: Available");
                Toast.makeText(MapsActivity.this, "Status Changed: Available", Toast.LENGTH_SHORT).show();
                break;
        }
    }

};

private void showMarkerMe(double lat, double lng){
    if (markerMe != null) {
        markerMe.remove();
    }

    MarkerOptions markerOpt = new MarkerOptions();
    markerOpt.position(new LatLng(lat, lng));
    markerOpt.title("I am here!");
    markerMe = mMap.addMarker(markerOpt);

    //Toast.makeText(this, "lat:" + lat + ",lng:" + lng, Toast.LENGTH_SHORT).show();
}

private void cameraFocusOnMe(double lat, double lng){
    CameraPosition camPosition = new CameraPosition.Builder()
            .target(new LatLng(lat, lng))
            .zoom(16)
            .build();

    mMap.animateCamera(CameraUpdateFactory.newCameraPosition(camPosition));
}

private void trackToMe(double lat, double lng){
    if (traceOfMe == null) {
        traceOfMe = new ArrayList<LatLng>();
    }
    traceOfMe.add(new LatLng(lat, lng));

    calculateDistance(traceOfMe);

    PolylineOptions polylineOpt = new PolylineOptions();
    for (LatLng latlng : traceOfMe) {
        polylineOpt.add(latlng);
    }

    polylineOpt.color(Color.RED);

    Polyline line = mMap.addPolyline(polylineOpt);
    line.setWidth(10);
}

private void calculateDistance(ArrayList<LatLng> points) {

    for (int i =0; i < points.size() -1; i++) {
        LatLng pointA =  points.get(i);
        LatLng pointB = points.get(i + 1);
        float[] results = new float[3];
        Location.distanceBetween (pointA.latitude, pointA.longitude, pointB.latitude, pointB.longitude, results);
        totalD +=  results[0];
    }
}

private void updateWithNewLocation(Location location) {

    String where = "";
    if (location != null) {

        double lng = location.getLongitude();

        double lat = location.getLatitude();

        float speed = location.getSpeed();

        long time = location.getTime();
        String timeString = getTimeString(time);

        speedList.add(""+ speed);

        where = "Lng: " + lng +
                "  Lat: " + lat +
                "  Speed: " + speed +
                "\nTime: " + timeString +
                "  Provider: " + "gps" +
                "  Distance: " + totalD ;


        showMarkerMe(lat, lng);
        cameraFocusOnMe(lat, lng);
        trackToMe(lat, lng);

    }else{
        where = "No location found.";
    }


    txt.setText(where);
}

我使用上面的代码来跟踪路线，我想使用distanceBetween计算总距离，但我不知道该怎么做。

Answer 1

你必须经历你的轨迹的所有要点。并为路径的每个段调用distanceBetween。

distanceBetween方法采用float []参数并将结果存储在其中。

results [0] =以米为单位的两点之间的距离。

结果1 =初始方位（似乎并非总是设定）

结果[2] =最终方位（似乎并不总是设定）

有关详细信息，请参阅文档there

所以这样的事情应该做的工作

private float calculateDistance(ArrayList<LatLng> points) {
    float totalDistance = 0f;
    for (int i =0; i < points.size() -1; i++ {
        LatLng pointA =  points.get(i);
        LatLng pointB = points.get(i + 1);
        float[] results = new float[3];
        Location.distanceBetween (pointA.latitude, pointA.longitude, pointB.latitude, pointB.longitude, results);
        totalDistance +=  results[0];
    }
    return totalDistance;
}

这是一个更优化的解决方案：

在您的活动中，您存储了两个变量

LatLng previousLocation float totalDistance

然后在你的onLocationChanged方法中。你可以像那样调用addToDistance方法

// Goes inside your Location listener
@Override
public void onLocationChanged(Location location) {
    updateWithNewLocation(location);
    addToDistance(location);
}

// Goes inside your activity
public void addToDistance(LatLng newPoint) {
        if (previousLocation !=  null) { 
            float[] results = new float[3];
            Location.distanceBetween (previousLocation.latitude, previousLocation.longitude, newPoint.latitude, newPoint.longitude, results);
        totalDistance +=  results[0];
        } 
        previousLocation = newPoint;
}

Android从ArrayList获取元素<latlng>（）

1 个答案: