在php中查询条件时无法从mongodb获取记录

Question

我有collection名称restaurant，它有120万条记录。我想根据我的地理位置（即纬度/长度）找到距离1英里半径近的餐厅

示例：在这里，我分享了120万restaurant集合中的2个文档：

{
    "_id" : ObjectId("5937aa44ae5fbf080d017fdc"),
    "factual_id" : "d37774d0-e379-4325-83ed-6fee2f6820f6",
    "name" : "Orange Deli Grocery",
    "address" : "145 Avenue D",
    "address_extended" : null,
    "po_box" : null,
    "locality" : "New York",
    "region" : "NY",
    "post_town" : null,
    "admin_region" : null,
    "postcode" : NumberInt("10009"),
    "country" : "us",
    "tel" : "(212) 228-2710",
    "fax" : null,
    "latitude" : 40.724909,
    "longitude" : -73.97533,
    "loc" : {
        "type" : "Point",
        "coordinates" : [
            -73.97533,
            40.724909
        ]
    }
},

/* 2 createdAt:6/7/2017, 1:06:53 PM*/
{
    "_id" : ObjectId("5937ad15ae5fbf8003000ff9"),
    "factual_id" : "18393fb5-6061-4281-84f5-d860d78e88a0",
    "name" : "El Rinconcito",
    "address" : "408 E 10th St",
    "address_extended" : "Frnt 2",
    "po_box" : null,
    "locality" : "New York",
    "region" : "NY",
    "post_town" : null,
    "admin_region" : null,
    "postcode" : NumberInt("10009"),
    "country" : "us",
    "tel" : "(212) 254-1381",
    "fax" : "(646) 590-3673",
    "latitude" : 40.725591,
    "longitude" : -73.976997,
    "loc" : {
        "type" : "Point",
        "coordinates" : [
            -73.976997,
            40.725591
        ]
    }
} 

现在，当我在mongo shell中运行以下查询时，我得到5000条记录。

var query = {
    "loc" : {
        $geoWithin : {
            $centerSphere : [[-73.993068,40.722355], 1/3959 ]
        }
    }
};
// Step 2: Query points.
db.restaurant.find(query)

但是当我尝试使用PHP同样的事情时，我会得到空的回复

$args = array(
    'loc' => array(
        "\$geoWithin" => array(
            "\$centerSphere" => array(
                array(-73.993068,40.722355), 1/3959 
            )
        )
    )
);

// here i have successfully connection with mongo
$collection = new MongoCollection($this->mongo_db->db, 'restaurant');
$cursor = $collection->find($args);
foreach ($cursor as $doc) {
    var_dump($doc);
}