haversine.php

<?php  

/**
 * Calculates the great-circle distance between two points
 * using the Haversine formula.
 *
 * @param float $latitudeFrom Latitude of start point in [deg decimal]
 * @param float $longitudeFrom Longitude of start point in [deg decimal]
 * @param float $latitudeTo Latitude of target point in [deg decimal]
 * @param float $longitudeTo Longitude of target point in [deg decimal]
 * @param float $earthRadius Mean earth radius in [m]
 *
 * @return float Distance between points in [m] (same as earthRadius)
**/
private function haversineGreatCircleDistance($latitudeFrom, $longitudeFrom, $latitudeTo, $longitudeTo, $earthRadius = 6371000)
{
    // Convert from degrees to radians.
    $latFrom = deg2rad($latitudeFrom);
    $lonFrom = deg2rad($longitudeFrom);
    $latTo = deg2rad($latitudeTo);
    $lonTo = deg2rad($longitudeTo);

    $latDelta = $latTo - $latFrom;
    $lonDelta = $lonTo - $lonFrom;

    $angle = 2 * asin(sqrt(pow(sin($latDelta / 2), 2) +
    cos($latFrom) * cos($latTo) * pow(sin($lonDelta / 2), 2)));
    return $angle * $earthRadius;
}