引自http://hi.baidu.com/mytudousipro/blog/item/5d38fa89c7344c9ca4c272f6.html
http://blog.csdn.net/suen/archive/2006/11/29/1420455.aspx
http://maweifeng.cnblogs.com/archive/2006/02/24/337181.html
http://www.gisdev.cn/space/?uid=4#