Calculating distance between two GPS coordinates

Now that I have a PHP script that can find out my physical location, I wanted to calculate how far from home I am. Since ‘home’ is a fixed GPS coordinate and my actual position varies, I needed a method to calculate the distance between two GPS coordinates. I found this suggested PHP code for the purpose and tested it out, it works pretty neat. I have updated my PHP script now to calculate the distance in meters between my current location and my home, it outputs something like this now:

Current location is:42.****,23.*****, accuracy is 40 m (Sofia, Bulgaria) from 12/18/12 08:13:31
Distance from home:19994.1161466m

(I have masked my actual location for privacy purposes)

So the PHP script now not only knows whre I am, but how far I am, may come in handy in my future home automation improvements.

/**
 * Calculates the great-circle distance between two points, with
 * the Vincenty formula.
 * @param float $latitudeFrom Latitude of start point in [deg decimal]
 * @param float $longitudeFrom Longitude of start point in [deg decimal]
 * @param float $latitudeTo Latitude of target point in [deg decimal]
 * @param float $longitudeTo Longitude of target point in [deg decimal]
 * @param float $earthRadius Mean earth radius in [m]
 * @return float Distance between points in [m] (same as earthRadius)
 */
function vincentyGreatCircleDistance(
  $latitudeFrom, $longitudeFrom, $latitudeTo, $longitudeTo, $earthRadius = 6371000)
{
  // convert from degrees to radians
  $latFrom = deg2rad($latitudeFrom);
  $lonFrom = deg2rad($longitudeFrom);
  $latTo = deg2rad($latitudeTo);
  $lonTo = deg2rad($longitudeTo);

  $lonDelta = $lonTo - $lonFrom;
  $a = pow(cos($latTo) * sin($lonDelta), 2) +
    pow(cos($latFrom) * sin($latTo) - sin($latFrom) * cos($latTo) * cos($lonDelta), 2);
  $b = sin($latFrom) * sin($latTo) + cos($latFrom) * cos($latTo) * cos($lonDelta);

  $angle = atan2(sqrt($a), $b);
  return $angle * $earthRadius;
}