The present invention relates to a method for determining an imaging direction of an imaging apparatus (10), such as an x-
ray apparatus, with a
radiation source or an imaging source (12) that emits an imaging beam (14) to an imaging
detector (16) along a beam path, comprising the steps of imaging an object (18) from a first direction to obtain a first 2D image; providing 3D reference data, for example a generic or statistical 3D model or an earlier obtained 3D
data set, of the imaged object (18); performing a 2D / 3D matching of the first 2D image with the 3D reference data to determine a position of an imaging plane (20, 22, 24) of the first 2D image relative to the 3D reference data; and determining the imaging direction of the imaging apparatus (10) relative to the object (18) based on the position of the imaging plane (20, 22, 24) relative to the 3D reference data, as well as to a
navigation system for computer-assisted
surgery comprising the imaging
system of the preceding claim; a
tracking system (11), such as optical or IR tracking means; detection devices (13, 15) such as e.g. radiopaque markers (13) detectable by the imaging
system and markers (15) detectable by the
tracking system (11) attachable to an object (18), wherein the
navigation system is adapted to detect a position of the object (18) based on the detection devices (13, 15), in order to generate detection signals and to supply the detection signals to the computer (17) such that the computer can determine
point data on the basis of the detection signals received; a calibration object such as a patient body or a phantom bearing detection devices for calibrating the
navigation system.