  The Moyal equation describes the evolution of the Wigner function of a
quantum system in the phase space. The right-hand side of the equation contains
an infinite series with coefficients proportional to powers of the Planck
constant. There is an interpretation of the Moyal equation as a quantum
analogue of the classical Liouville equation. Indeed, if one uses the notion of
the classical passage to the limit as the Planck constant tends to zero, then
formally the right-hand side of the Moyal equation tends to zero. As a result,
the Moyal equation becomes the classical Liouville equation for the
distribution function. In this paper, we show that the right side of the Moyal
equation does not explicitly depend on the Planck constant, and all terms of
the series can make a significant contribution. The transition between the
classical and quantum descriptions is related not to the Planck constant, but
to the spatial scale.
  For a model quantum system with a potential in the form of a
{\guillemotleft}quadratic funnel{\guillemotright}, an exact 3D solution of the
Schr\"odinger equation is found and the corresponding Wigner function is
constructed in the paper. Using trajectory analysis in the phase space, based
on the representation of the right-hand side of the Moyal equation, it is shown
that on the spatial microscale there is an infinite number of
{\guillemotleft}trajectories{\guillemotright} of the particle motion (thereby
the concept of a trajectory is indefinite), and when passing to the macroscale,
all {\guillemotleft}trajectories{\guillemotright} concentrate around the
classical trajectory.
