ref:android方向传感器

http://www.ibm.com/developerworks/cn/opensource/os-android-sensor/

http://blog.csdn.net/tinya0913/archive/2010/12/23/6095307.aspx

http://blog.csdn.net/stevenliyong/archive/2009/09/15/4555331.aspx

http://blog.csdn.net/tinya0913/archive/2010/12/23/6095307.aspx