1. A method of producing an object data set describing a straightened reformat from an original object data set containing an elongated subject, from which an initial cross sectional slice is created transverse to the elongated subject and at least one further cross sectional slice is created transverse to the elongated subject, the method comprising: determining with a processor a reference direction in each cross sectional slice; and creating the object data set by concatenating the cross sectional slices, each cross sectional slice being orientated so that the reference directions in the cross sectional slices are aligned.