  The possibility of constructing a complete, continuous Wigner function for
any quantum system has been a subject of investigation for over 50 years. A key
system that has served to illustrate the difficulties of this problem has been
an ensemble of spins. Here we present a general and consistent framework for
constructing Wigner functions exploiting the underlying symmetries in the
physical system at hand. The Wigner function can be used to fully describe any
quantum system of arbitrary dimension or ensemble size.
