Calculate distance between coordinates

distance_calculator.php

* Calculate distance between two users
 */
function distanceBetween( $user_num_1, $user_num_2 ) {
    $sql = "SELECT user_num,lat,lng,locationDiscovery FROM user_profile WHERE user_num in ('$user_num_1','$user_num_2')";
    $qry = $this->db->query( $sql );

    $users = array();
    foreach( $qry->result() as $row ) {
        $users[$row->user_num] = $row;
    }

    if( !array_key_exists($user_num_1, $users) OR  !array_key_exists($user_num_2, $users) ) {
        return -1;
    }

    // if users location discovery is off, or lat/long are not available, we can not calculate distance
    if( $users[$user_num_2]->locationDiscovery == 0 ) {
        return -1;
    }

    $lat1 = $users[$user_num_1]->lat;
    $lng1 = $users[$user_num_1]->lng;

    $lat2 = $users[$user_num_2]->lat;
    $lng2 = $users[$user_num_2]->lng;

    return $this->haversineGreatCircleDistance( $lat1, $lng1, $lat2, $lng2 );
}