PHP function to determine whether or not 2 lat/lon points are within a specified distance of each other (Great Circle)

index.php

<?php

$pointA = array(
	'lat' => 51.863119,
	'lon' => -2.21064
);

$pointB = array(
	'lat' => 51.957807,
	'lon' => -2.640603
);

$radius = 10;

if(withinRadius($pointA,$pointB,$radius))
{
	echo("within ".$radius);
} else {
	echo("not within ".$radius);
}

function withinRadius($pointA, $pointB, $within)
{	
	$earthR = 6371000; // radius of earth

	// convert to radians
	$latA = deg2rad($pointA['lat']);
	$lonA = deg2rad($pointA['lon']);
	$latB = deg2rad($pointB['lat']);
	$lonB = deg2rad($pointB['lon']);

	// get difference between lat/lon radians
	$deltaLat = $latA - $latB;
	$deltaLon = $lonA - $lonB;

	$distance = 2 * asin(sqrt(pow(sin($deltaLat / 2), 2) +
    cos($latA) * cos($latB) * pow(sin($deltaLon / 2), 2))) * $earthR;

	return $distance <= $within ? TRUE : FALSE;
}