A method and apparatus for defining the location of a medical instrument relative to features of a medical workspace including a patient's body region are described. Pairs of two-dimensional images are obtained, preferably by means of two video cameras making images of the workspace along...http://www.google.com.au/patents/US5836954?utm_source=gb-gplus-sharePatent US5836954 - Apparatus and method for photogrammetric surgical localization
