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/**
 * 根据两点间的经纬度计算距离
 *
 * @param float $lat
 *            纬度值
 * @param float $lng
 *            经度值
 */
function getDistance($lat1, $lng1, $lat2, $lng2)
{
    $earthRadius = 6367000; // approximate radius of earth in meters
    $earthRadius = 6378138;
    
    /*
     * Convert these degrees to radians to work with the formula
    */

    $lat1 = ($lat1 * pi()) / 180;
    $lng1 = ($lng1 * pi()) / 180;

    $lat2 = ($lat2 * pi()) / 180;
    $lng2 = ($lng2 * pi()) / 180;

    /*
     * Using the Haversine formula http://en.wikipedia.org/wiki/Haversine_formula calculate the distance
    */

    $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;

    return showDistance(round($calculatedDistance));
}

function showDistance($distance)
{
    if ($distance == '') {
        return $distance;
    }
    if ($distance >= 1000) {
        $distance = number_format($distance / 1000, 2) . 'KM';
    } else {
        $distance .= 'M';
    }
    return $distance;
}