PHP - Haversine Distance between two points ( latitude, longitude )

<?php /** * Distance between two points * * @param float $lat1 Latitude 1 * @param float $lng1 Longitude 1 * @param float $lat2 Latitude 2 * @param float $lng2 Longitude 2 * @param string $unit [mi|km] miles|kilometers * * @return float distance in mi|km. Default is miles. */ function harversineDistance($lat1, $lng1, $lat2, $lng2, $unit = 'mi') { $latd = deg2rad($lat2 - $lat1); $lngd = deg2rad($lng2 - $lng1); $a = sin($latd / 2) * sin($latd / 2) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * sin($lngd / 2) * sin($lngd / 2); $c = 2 * atan2(sqrt($a), sqrt(1 - $a)); $radius = ( $unit === 'km' ) ? 6371.009 : 3958.761; // miles return round($radius * $c, 3); }