1. A system, comprising: a probe comprising a housing and a physical pointer having a defined length; a video camera provided in the housing; a tracking system arranged to track the three-dimensional positions of the video camera and various reference points on a subject; a data processor with pre-stored three dimensional subject image data; and a display; wherein the data processor augments real time images from the video camera with virtual objects generated from the three dimensional subject image data in response to input from the tracking device and displays a composite image on the display; and wherein the physical pointer is attached to the housing at a defined offset from the housing so that all or a portion of it can been seen at a defined position within the view of the video camera.