title: track small movements of iphone with no GPS
body: <p>I have to write an application for iphone that tracks the movement of the iphone itself, given its initial position, without ever using GPS. That is, I can only use data provided by the gyroscope and the accelerometer.  The distances I need to measure are rather small and the precision I'm looking for is 40-50cm (~2 feet) at the very most.</p>
  
  <p>Is this possible? If so, what's the best way to go about it? Also, do you know of any existing (and possibly open source) projects that have implemented this already?</p>
  
  <p>Thanks a lot!</p>