after the reconstruction center generates the three dimensional image the data representing this three dimensional image are communicated back to the physician for generating the three dimensional image it is necessary to reference the respective 2d projections relative to each other in terms of their spatial relationship calibration there are several techniques available for undertaking this step an autocalibration can ensue at the reconstruction center in such a manner that natural landmarks are automatically detected and point correspondences calculated with image processing methods segmentation the 3d coordinates of the points as well as the projection parameters extrinsic and intrinsic camera parameters are subsequently assessed in a further autocalibration natural landmarks are manually detected and the point correspondences calculated with image processing methods segmentation at the reconstruction center the 3d coordinates of the points as well as the projection parameters are again subsequently assessed in a third embodiment of an autocalibration markers are applied to the patient when the 2d projections are obtained and these markers are automatically detected and the point correspondences calculated with image processing methods segmentation at the reconstruction center the 3d coordinates of the points as well as the projection parameters extrinsic and intrinsic camera parameters are again subsequently assessed calibration with a reference sample can also ensue by a calibration sample with known 3d geometry being located together with the patient data in the exposure the point features are automatically detected and the.