  Topological phases of materials are characterized by topological invariants
that are conventionally calculated by different means according to the
dimension and symmetry class of the system. For topological materials described
by Dirac models, we introduce a wrapping number as a unified approach to obtain
the topological invariants in arbitrary dimensions and symmetry classes. Given
a unit vector that parametrizes the momentum-dependence of the Dirac model, the
wrapping number describes the degree of the map from the Brillouin zone torus
to the sphere formed by the unit vector that we call Dirac sphere. This method
is gauge-invariant and originates from the intrinsic features of the Dirac
model, and moreover places all known topological invariants, such as Chern
number, winding number, Pfaffian, etc, on equal footing.
