1. A method for determining geometric imaging properties of a flat panel detector in an x-ray inspection system, the method comprising: arranging a calibration phantom between an x-ray source and the flat panel detector, wherein the calibration phantom comprises at least one discrete geometric object; recording at least one x-ray image of the calibration phantom with the flat panel detector, wherein at least one discrete geometric shape is generated in the x-ray image by imaging the at least one discrete geometric object of the calibration phantom; and determining a location-dependent distortion error of the flat panel detector from the at least one x-ray image on the basis of at least one characteristic of the at least one discrete geometric shape; wherein all of the at least one characteristic of the at least one discrete geometric shape used for determining the location-dependent distortion error are independent of the dimensions of the calibration phantom.