  We apply the semi-classical limit of the generalized $SO(3)$ map for
representation of variable-spin systems in a four-dimensional symplectic
manifold and approximate their evolution terms of effective classical dynamics
on $T^{\ast }\mathcal{S}_{2}$. Using the asymptotic form of the star-product,
we manage to "quantize" one of the classical dynamic variables and introduce a
discretized version of the Truncated Wigner Approximation (TWA). Two emblematic
examples of quantum dynamics (rotor in an external field and two coupled spins)
are analyzed, and the results of exact, continuous, and discretized versions of
TWA are compared.
