function distance($lat1,$lng1,$lat2,$lng2) //(x1,y1,x2,y2)
{
  $lat1  = deg2rad($lat1); 
  $lng1  = deg2rad($lng1);
  $lat2  = deg2rad($lat2);
  $lng2  = deg2rad($lng2); 
  $delta_lat  = ($lat2 - $lat1); 
  $delta_lng  = ($lng2 - $lng1); 
  return round( 6378137 * acos( cos( $lat1 ) * cos( $lat2 ) * cos( $lng1 - $lng2 ) + sin( $lat1 ) * sin( $lat2 ) ) ); 
}