I\'m working on a project right now in which we are developing an autonomous robot. I have to basically find out the distance travelled by the robot between any 2 intervals. I\'
The answer offered by Jacob is the right path to pursue, but you are likely to find that the resulting distance-traveled information is fairly noisy. You may want to consider using Kalman filters to improve your localization estimates over time.
There is a very large body of literature on Kalman filters, but I've listed one relevant paper below.
Larry H. Matthies, Richard Szeliski, and Takeo Kanade (1989). "Kalman Filter-based Algorithms for Estimating Depth from Image Sequences ", International Journal of Computer Vision, Vol 3, No. 3, September, pp 209–236.