  We show that a reference frame transformation could turn a topologically
trivial Dirac fermion into a topologically nontrivial Weyl semimetal. This is
elucidated by the transformation of the Dirac equation into the equation for
Weyl semimetals through specific infinitesimal local Lorentz transformations of
the orthonormal basis. This kind of transformation, interpreted as a change of
reference frame, could induce an observational effect that an axial gauge field
and/or a vector U(1) gauge field appears effectively, which are in fact
inertial forces in the non-inertial frame.The precise local Lorentz
transformations and the movement of observers needed to realize the two
additional fields are provided respectively. This novel effect can be viewed as
a generalization of the effect found in relativistic hydrodynamics that
topologically trivial modes in an inertial frame could become topologically
nontrivial observed by a special non-inertial observer.
