PHP で 2 つの座標間の距離を正確に計算するにはどうすればよいですか?

class CoordDistance
{
    public $lat_a;
    public $lon_a;
    public $lat_b;
    public $lon_b;

    public $measure_unit = 'kilometers';
    public $measure_state = false;
    public $measure;
    public $error;

    public function DistAB()
    {
        $delta_lat = $this->lat_b - $this->lat_a;
        $delta_lon = $this->lon_b - $this->lon_a;

        $earth_radius = 6372.795477598;

        $alpha = $delta_lat / 2;
        $beta = $delta_lon / 2;
        $a = sin(deg2rad($alpha)) * sin(deg2rad($alpha)) + cos(deg2rad($this->lat_a)) * cos(deg2rad($this->lat_b)) * sin(deg2rad($beta)) * sin(deg2rad($beta));
        $c = asin(min(1, sqrt($a)));
        $distance = 2 * $earth_radius * $c;
        $distance = round($distance, 4);

        $this->measure = $distance;
    }
}

/**
 * Calculates the great-circle distance between two points, using the Vincenty 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)
 */
public static function vincentyGreatCircleDistance(
    $latitudeFrom, $longitudeFrom, $latitudeTo, $longitudeTo, $earthRadius = 6371000
) {
    // Convert from degrees to radians
    $latFrom = deg2rad($latitudeFrom);
    $lonFrom = deg2rad($longitudeFrom);
    $latTo = deg2rad($latitudeTo);
    $lonTo = deg2rad($longitudeTo);

    $lonDelta = $lonTo - $lonFrom;
    $a = pow(cos($latTo) * sin($lonDelta), 2) +
        pow(cos($latFrom) * sin($latTo) - sin($latFrom) * cos($latTo) * cos($lonDelta), 2);
    $b = sin($latFrom) * sin($latTo) + cos($latFrom) * cos($latTo) * cos($lonDelta);

    $angle = atan2(sqrt($a), $b);
    return $angle * $earthRadius;
}