MongoDB php Spatial天文数据这有什么问题？

I want to retrieve data within the bounding box ((ra_min,dec_min),(ra_max,dec_max)). Could anyone tell me what's wrong with below?

php Code and structure of data are below. Thanks......

Structure :

    {
        "filter": "E", 
        "loc": {
            "dec": 130, 
            "ra": 15
        }, 
        "path": "00015+00130E.jpeg"
    }, 
    {
        "filter": "Z", 
        "loc": {
            "dec": 130, 
            "ra": 15
        }, 
        "path": "00015+00130Z.jpeg"
    },

Code :

$lowerLeft = array("ra"=>$RA_min - $ra_offset, "dec"=>$DEC_min - $dec_offset);
$upperRight= array("ra"=>$RA_max + $ra_offset, "dec"=>$DEC_max + $dec_offset);

$cond = array("loc" => array('$within' => array('$box' => $lowerLeft, $upperRight)));
$cursor = $collection->find($cond);

i Think problem is on $box Usage

$box Usage Example:

$cursor = $collection->find( array( 'loc'=>array('$within'=> array('$box'=>array(array(0,0), array(100,100) ) ) ) ));

This will return all the documents that are within the box having points at: [0,0], [0,100], [100,0], and [100,100].

use print_r($cond); before find(); for see the array value that show you where is problem