Calculating Distance Between Two Latitude and Longitude Points

gistfile1.php

<?php

function distance($lat1, $lon1, $lat2, $lon2, $unit)
{
  $theta = $lon1 - $lon2;
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist = acos($dist);
  $dist = rad2deg($dist);
  $miles = $dist * 60 * 1.1515;
  $unit = strtoupper($unit);

  if ($unit == "K") {
    return ($miles * 1.609344);
  } else if ($unit == "N") {
      return ($miles * 0.8684);
    } else {
        return $miles;
      }
}

echo distance(41.928, -87.7044, 42.8807, -88.2014, "M") . " Miles<br>";
echo distance(41.928, -87.7044, 42.8807, -88.2014, "K") . " Kilometers<br>";

?>

<script>
// See: http://stackoverflow.com/questions/27928/how-do-i-calculate-distance-between-two-latitude-longitude-points
function getDistanceFromLatLonInKm(lat1,lon1,lat2,lon2)
{
  var R = 3963; // Radius of the earth in miles
  var dLat = deg2rad(lat2-lat1);  // deg2rad below
  var dLon = deg2rad(lon2-lon1);
  var a =
    Math.sin(dLat/2) * Math.sin(dLat/2) +
    Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) *
    Math.sin(dLon/2) * Math.sin(dLon/2)
    ;
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
  var d = R * c; // Distance in miles
  return d;
}

function deg2rad(deg) {
  return deg * (Math.PI/180)
}

console.log(getDistanceFromLatLonInKm(41.928, -87.7044, 42.8807, -88.2014));
</script>