/**
 * 計(jì)算距離
 * @param  Decimal $lat1 起點(diǎn)緯度
 * @param  Decimal $lng1  起點(diǎn)經(jīng)度
 * @param  Decimal $lat2 終點(diǎn)緯度 
 * @param  Decimal $lng2  終點(diǎn)經(jīng)度
 */
function getDistance($lat1, $lng1, $lat2, $lng2){ 
    $earthRadius = 6367000; //近似地球半徑（米）
    $lat1 = ($lat1 * pi() ) / 180; 
    $lng1 = ($lng1 * pi() ) / 180; 
    $lat2 = ($lat2 * pi() ) / 180;
    $lng2 = ($lng2 * pi() ) / 180; 
    $calcLongitude = $lng2 - $lng1;     //長(zhǎng)度
    $calcLatitude = $lat2 - $lat1;      //緯度
    $stepOne = pow(sin($calcLatitude / 2), 2) + cos($lat1) * cos($lat2) * pow(sin($calcLongitude / 2), 2); 
    $stepTwo = 2 * asin(min(1, sqrt($stepOne))); 
    $Distance = $earthRadius * $stepTwo; 
    
    if ($Distance >= 1000) {
        $Distance = round($Distance/1000,2);
        return $Distance . 'km';
    }

    return round($Distance) . 'm'; 
}