Haversine Distance between two points ( latitude, longitude )

distance-between-two-points.php

<?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);
}

https://codepad.co/snippet/qxtkRxVG