如何使用explode将字符串转换为数组？

How to convert this string into array using php? thank you in advance here is string:

((-111.448843339275,56.8746856298617))

$str = '((-111.448843339275,56.8746856298617))';
$str = str_replace ( array('((','))') , '', $str);
$array = explode(',',$str);