Angle calculations for an area detector on a two-axis arm: application to powder diffraction

A procedure for the reduction (integration) of a two-dimensional powder diffraction pattern registered with an area detector after rotation about two orthogonal diffractometer axes is described. The procedure involves the conversion from pixel coordinates to scattering and azimuthal angle {2θ, ψ} coordinates. The article concludes with a mention of two possible applications of the procedure to studies of reciprocal space mapping with an area detector.