php 地址转换经纬度

//$ak开发密钥,$cityname城市名称(支持省县乡详细地址)
public  function   getposition($ak,$cityname){
	$callback=array('lng'=>0,'lat'=>0);
	$apiUrl='http://api.map.baidu.com/geocoder/v2/?address='.$cityname.'&output=json&ak='.$ak;
	$ret=json_decode(file_get_contents($apiUrl),true);
	if($ret['status']==0){
		$callback['lng']=$ret['result']['location']['lng'];
		$callback['lat']=$ret['result']['location']['lat'];			
	}
	return $callback;			
}