  Planewave propagation in a simply moving, dielectric-magnetic medium that is
isotropic in the co-moving reference frame, is classified into three different
categories: positive-, negative-, and orthogonal-phase-velocity (PPV, NPV, and
OPV). Calculations from the perspective of an observer located in a
non-co-moving reference frame show that, whether the nature of planewave
propagation is PPV or NPV (or OPV in the case of nondissipative mediums)
depends strongly upon the magnitude and direction of that observer's velocity
relative to the medium. PPV propagation is characterized by a positive real
wavenumber, NPV propagation by a negative real wavenumber. OPV propagation only
occurs for nondissipative mediums, but weakly dissipative mediums can support
nearly OPV propagation.
