Check two geo-coordinate points are within a specified range

check-in-range.php

<?php

check_in_distance($lat_a, $long_a, $lat_b, $long_b, $range)
{
    $dlat = ($lat_a / (180 / pi())) - ($lat_b / (180 / pi()));
    $dlong = ($long_a / (180 / pi())) - ($long_b / (180 / pi()));
    $c = pow(sin($dlat / 2), 2) + cos($lat_a);
    $c = $c * cos($lat_b) * pow(sin($dlong / 2), 2);
    $c = 2 * asin(sqrt($c));
    $c = 6371 * $c;

    return $c <= $range;
}