X-ray stress analysis with a 2D detector. Part 1. Data acquisition and treatment strategies

In the field of stress analysis via X-ray diffraction from polycrystalline specimens, the use of a 2D detector allows the operator to break free from the equatorial plane and devise new acquisition and treatment strategies for both synchrotron facilities and in-house laboratory equipment. Most of the time, however, the data acquired with these detectors are treated through radial–azimuthal binning in order to go back to classical pattern fitting strategies. The aim of the present paper is to propose a new approach to these issues, called RingFit-2D. First, it is shown that the set of angles used classically is no longer adapted to 2D detectors and a new set is proposed. A geometric description of the setup is then used to perform a global fitting of the images and to show that some issues linked to the spatial calibration of the detector can be easily detected through this approach. It is also shown that some specific formulations proposed in the literature can be derived from the general formulation described in the present paper. The second part of this work [François (2023). J. Appl. Cryst. 
 56, http://doi.org/10.1107/S1600576722010925] will deal with the modelling and quantification of alignment errors in the diffractometer.