Map - distance

<?php

class Map
{
    const UNIT_MILE          = 0;
    const UNIT_KILOMETER     = 1;
    const UNIT_NAUTICAL_MILE = 2;

    /**
     * Calculate distance between two coords positions
     *
     * @param float $lat1   Latitude of the first coord
     * @param float $lon1   Longitude of the first coord
     * @param float $lat2   Latitude of the second coord
     * @param float $lon2   Longitude of the second coord
     * @param int $unit     Unit of measure of the returned value
     *
     * @return float        Distance measured
     */
    public function distance($lat1, $lon1, $lat2, $lon2, $unit = self::UNIT_MILE)
    {
        $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;

        switch ($unit) {
           case self::UNIT_KILOMETER:
                return ($miles * 1.609344);
                break;

            case self::UNIT_NAUTICAL_MILE:
                return ($miles * 0.8684);
                break;

            case self::UNIT_MILE:
            default:
                return $miles;
                break;
        }
     }
}