  An instrument and software algorithm is described for the purpose of
characterization of large single crystals at the Alignment Facility (ALF) of
the ISIS spallation neutron source. We describe a method for both
characterizing the quality of the sample and also aligning it in a particular
scattering plane. We present a software package written for this instrument and
demonstrate its utility by way of an example of the structural characterization
of large singles crystals of Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$. We suggest
extensions and modifications of characterization instruments for future
improved beamlines. It is hoped that this software will be used by the neutron
user community for pre characterizing large single crystals for spectroscopy
experiments and that future facilities will include such a facility as part of
the spectroscopy suite at spallation neutron sources.
