A method of determining the spatial orientation of a two-dimensional detector in an X-ray diffractometry system, and calibrating the detector position in response thereto, uses diffraction patterns from a powder sample collected at a plurality of detector swing angles. The overlapping of the detected patterns indicates relative errors in the detector orientation. In particular, intersection points between the different diffraction patterns may be located, and their relative locations may be used to identify errors. Such errors may be in the detector position, or they may be errors in different rotational directions, such as roll, pitch or yaw. Determination and correction of the detector orientation using this method may be part of a calibration routine for the diffractometry system. Roll error may also be determined using a single measurement with the detector at a swing angle perpendicular to the X-ray beam.