PHP 根据两点间的经纬度计算距离

/**
 * 根据两点间的经纬度计算距离
 * @param float $lat1 纬度值
 * @param float $lng1 经度值
 * @param float $lat2 纬度值
 * @param float $lng2 经度值
 */
function getDistance($lat1, $lng1, $lat2, $lng2)
{
    $earthRadius = 6367000;
    $lat1 = ($lat1 * pi() ) / 180;
    $lng1 = ($lng1 * pi() ) / 180;
    $lat2 = ($lat2 * pi() ) / 180;
    $lng2 = ($lng2 * pi() ) / 180;
    $calcLongitude = $lng2 - $lng1;
    $calcLatitude = $lat2 - $lat1;
    $stepOne = pow(sin($calcLatitude / 2), 2) + cos($lat1) * cos($lat2) * pow(sin($calcLongitude / 2), 2);
    $stepTwo = 2 * asin(min(1, sqrt($stepOne)));
    $calculatedDistance = $earthRadius * $stepTwo;
    $range=round($calculatedDistance,2);
    if($range>1000){
        $range = round($range/1000,2)."km";
    }else{
        $range  =   $range.'m';
    }
    return $range;
}