1. A method for measuring mechanical workpieces having a defined rotationally symmetric structure, the method comprising the steps of: providing a radiation source for generating radiation; providing a detector array for receiving the radiation, said detector array defining a two-dimensional imaging plane; positioning a workpiece between the radiation source and the detector array, so that the radiation penetrates the workpiece before it impinges on the detector array; moving the radiation source and the workpiece relative to one another in a step-by-step fashion; generating a number of two-dimensional images of the workpiece by means of the detector array for a plurality of movement positions of the workpiece; and computing a three-dimensional image of the structure from the two-dimensional images, wherein the step of computing comprises: detecting a high-contrast transition, which correspond to edges of the structure, in said two-dimensional images; registering points at said high-contrast transition from at least two two-dimensional images generated at two different movement positions; and determining a three-dimensional geometric equivalent body using the registered points; and comparing said equivalent body to a predefined nominal structure; wherein the geometric equivalent body only parameterizes said rotationally symmetric structure; and further wherein coordinates of a center point of the equivalent body are determined comprising the steps of: a) determining first coordinates of at least three points on a boundary of a first circular image of the structure in a first movement position of the workpiece; b) determining a first center point of the first circular image from the first coordinates; c) rotating the workpiece on the one hand, and the radiation source and the detector array on the other hand relative to one another by a predefined angular step from the first into a second movement position; d) determining second coordinates of at least three points on the boundary of a second circular image of the structure in the second movement position of the workpiece; e) determining a second center point of the second circular image from the second coordinates; f) determining a first center beam extending from the radiation source to the first center point and determining a second center beam extending from the radiation source to the second center point; g) determining a position of the smallest distance between the first and second center beams; and h) determining coordinates of a center of the smallest distance as the position of the center point of the equivalent body.