1. A method for determining a coordinate transformation between a coordinate system of a first object and a coordinate system of a second object to be navigated relative to said first object, comprising the steps of: providing a position acquisition system having a coordinate system associated therewith; providing an X-ray apparatus for obtaining an X-ray image of said first object; providing a marking on said X-ray apparatus detectable by said position acquisition system, said marking having a coordinate system associated therewith; executing a calibration run prior to obtaining said X-ray image; in said calibration run, determining a coordinate transformation L between the coordinate system of said marking and the coordinate system of said position acquisition system, and a coordinate transformation V between the coordinate system of said position acquisition system and the coordinate system of said first object; determining a modified coordinate transformation L′ between said coordinate system of said marking and said coordinate system of said position acquisition system resulting from an altered position of said X-ray apparatus and said position acquisition system relative to each other while obtaining said X-ray image of said first object using said X-ray apparatus; determining a coordinate transformation L″ between the coordinate system of the second object and the coordinate system of the position acquisition system; and determining a coordinate transformation between said coordinate system of said second object and the coordinate system of said first object using said coordinate transformations V, L, L′ and L″.