1. A method of providing guidance in real-time or near real-time in conjunction with an endoscopic procedure, comprising the steps of: providing previously acquired three-dimensional (3D) image data of a body lumen; receiving a continuous live sequence of endoscopic video image data of the body lumen during a procedure from an endoscope; and registering the previously acquired 3D image data of the body lumen and the live endoscopic video image data of the body lumen to provide guidance to a user of the endoscope wherein the step of registering includes estimating the 3D location of the endoscope using the live sequence of endoscopic video image data and the previously acquired 3D image data.