COMPANG: automated comparison of orientations

A search for similar orientations of a three-dimensional object is a usual task in structure analysis. An example is a comparison of peaks of rotation functions in molecular replacement. An automated comparison of orientations defined as a list or several lists of corresponding Eulerian angles can be performed using the interactive program COMPANG. When calculating the closeness of orientations, this program allows one to take into account the symmetry operations of the space group as well as non-crystallographic symmetry. The similarity of orientations can be considered at a given accuracy, thus allowing a user to identify the groups of close orientations, i.e. their clusters. The size of such clusters can be used as a criterion to choose the correct orientation in difficult cases of molecular replacement.