1. A navigation system for computer-assisted surgery, comprising: a computer comprising a processor, the processor being configured to perform the steps of: a) acquiring, at the processor, predetermined constraint information defining one or more positions and/or orientations of an object in space; b) acquiring, at the processor, orientation data of the object while the object is positioned or moved while fulfilling a predetermined constraint; and c) determining, by the processor, compensation information based on the predetermined constraint information and the acquired orientation data of the object; a detection device for detecting an orientation of the object and supplying the orientation data to the computer; and a user interface for receiving data from the computer in order to provide information to a user, wherein the received data are generated by the computer on the basis of a result of processing performed by the computer.