title: how to calculate two coordinates distance in objective c?
body: <p>as title how to? i have tried the code from google earth, but seem like the result is different with the google map calculation result. below provided the code i did</p>
  
  <pre><code>-(double)GetDistance:(double)lat1 long1:(double)lng1 la2:(double)lat2 long2:(double)lng2 {
      //NSLog(@"latitude 1:%.7f,longitude1:%.7f,latitude2:%.7f,longtitude2:%.7f",lat1,lng1,lat2,lng2);
      double radLat1 = [self rad:lat1];
      double radLat2 = [self rad:lat2];
      double a = radLat1 - radLat2;
      double b = [self rad:lng1] -[self rad:lng2];
      double s = 2 * asin(sqrt(pow(sin(a/2),2) + cos(radLat1)*cos(radLat2)*pow(sin(b/2),2)));
      s = s * EARTH_RADIUS;
      s = round(s * 10000) / 10000;
      return s;
  }
  
  -(double)rad:(double)d
  {
      return d *3.14159265 / 180.0;
  }
  </code></pre>
  
  <p>the EARTH_RADIUS value is 6378.138</p>
  
  <p>by using this function by provided two coordinates the result come out is 4.5kM
  but when i use google map get direction between two same coordinates, it show me the distance  is about 8km</p>
  
  <p>can anyone help to point out the problem of my code?</p>