Automatic processing of rotation diffraction data from crystals of initially unknown symmetry and cell constants

An algorithm has been developed for the automatic interpretation of a given set of observed reciprocal-lattice points. It extracts a reduced cell and assigns indices to each reflection by a graph-theoretical implementation of the local indexing method. All possible symmetries of the observed lattice compatible with the metric of the reduced cell are recognized and reported, together with the unit-cell constants and the linear index transformation relating the conventional to the reduced cell. This algorithm has been incorporated into the program XDS [Kabsch (1988). J. Appl. Cryst. 21, 916–924], which is now able to process single-crystal area-detector data without prior knowledge of the symmetry and the unit-cell constants.