CalculateDistance.php

    const EARTH_RADIUS = 6371000;
    
    /**
     * Calculates the great-circle distance between two points, with
     * 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]
     * @return float Distance between points in [m] (same as earthRadius)
     */
    public function calculateDistance(float $latitudeFrom, float $longitudeFrom, float $latitudeTo, float $longitudeTo) {
        // 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 * self::EARTH_RADIUS;
    }