android – 如何使用其经度和纬度值计算两个位置之间的距离

这里我的代码我使用下面的代码来计算两个位置之间的距离使用它们的纬度和经度。这是错误的距离。有时变得正确,有时变得无关紧要。

我们从数据库获取lat1和lng1。

//getting lat2 and lng2 from GPS as below

public class MyLocationListener implements LocationListener {

  @Override
  public void onLocationChanged(Location loc)
  {
    lat2=loc.getLatitude();
    lng2=loc.getLongitude();
    String Text = "My current location is: " +"Latitud = "+ loc.getLatitude() +"Longitud = " + loc.getLongitude();

    //System.out.println("Lat & Lang form Loc"+Text);
    //Toast.makeText( getApplicationContext(), Text,Toast.LENGTH_SHORT).show();
  }

  @Override
  public void onProviderDisabled(String provider)
  {
  }

  @Override
  public void onProviderEnabled(String provider)
  {
  }

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


  //Calculating distance
  double earthRadius = 3958.75;

  double dLat = Math.toRadians(lat1-lat2);
  double dLng = Math.toRadians(lng1-lng2);
  double a = Math.sin(dLat/2) * Math.sin(dLat/2) +
             Math.cos(Math.toRadians(lat2)) * Math.cos(Math.toRadians(lat1)) *
             Math.sin(dLng/2) * Math.sin(dLng/2);
  double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
  double dist = earthRadius * c;
这里距离公里(公里)

private double distance(double lat1, double lon1, double lat2, double lon2) {
    double theta = lon1 - lon2;
    double dist = Math.sin(deg2rad(lat1)) 
                    * Math.sin(deg2rad(lat2))
                    + Math.cos(deg2rad(lat1))
                    * Math.cos(deg2rad(lat2))
                    * Math.cos(deg2rad(theta));
    dist = Math.acos(dist);
    dist = rad2deg(dist);
    dist = dist * 60 * 1.1515;
    return (dist);
}

private double deg2rad(double deg) {
    return (deg * Math.PI / 180.0);
}

private double rad2deg(double rad) {
    return (rad * 180.0 / Math.PI);
}
http://stackoverflow.com/questions/6981916/how-to-calculate-distance-between-two-locations-using-their-longitude-and-latitu

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