json_encode在arrayObject和array（）上表现不同

I had a function in php:

我在php中有一个函数:

//simple method with array()
$sensors = array();
$query = "select id, x(transform(wkb_geometry,". $epsg . ")) as lon, y(transform(wkb_geometry,". $epsg . ")) as lat from mytable;";
$result = pg_query($query) or die('Query failed: ' . pg_last_error());
while ($row = pg_fetch_assoc($result)) {
            //var_dump($row);
            $mySensor = new sensor($row['id'],$row['lat'],$row['lon']);
            $sensors[] = $mySensor->geoJSON();
}

echo json_encode($sensors);
//sim