System for sensing at least two points on an object for determining the position and orientation of the object relative to another object. Two light emitters mounted in spaced relation to each other on an external portion of an invasive probe remaining outside an object into which an invasive tip is...http://www.google.co.uk/patents/US6442416?utm_source=gb-gplus-sharePatent US6442416 - Determination of the position and orientation of at least one object in space
