1. A method of estimating position and orientation of an image-capturing device comprising: (A) obtaining a set of images by using said image-capturing device by processing a preceding set of frames; each said frame including a set of image data; (B) estimating previous position and orientation states of said image-capturing device by using state and covariance matrices including a set of image data included in at least one said preceding frame; and (C) estimating current position and orientation states of said image-capturing device by performing a sequential update of said state and covariance matrices; wherein for each new frame, said sequential update of said state and covariance matrices is performed by removing position and orientation states associated with an oldest preceding frame and by adding position and orientation states for said new frame.