This project ist part of the SPP1124 "Medical navigation and robotics" encouraged by the DFG. The aim of this project is to provide the surgeon with the insertion of a three-dimensional model of preoperative acheived data into the operating microscope during a neurosurgical intervention. This method of augmenting the microscope's view via stereoscopic collimation has the advantage of bewaring the surgeon to turn his head towards the navigational monitor and to transfer the two-dimensional information provided by the navigational monitor to the three-dimensional situs. This transfer is not easy for most surgeons and contains some error sources according to accurracy of positioning the structures of interest.