Boosting into the local frame of a fluid parcel (shown as a square, with magnetic field line in red and electron gyromotion in blue). In this fluid frame, the orientation of the observer’s line of sight depends on the magnitude of ﹩{\gamma }_{\infty }\sin i﹩. If ﹩{\gamma }_{\infty }\sin i\gt 1﹩, then the observer lies above the emitting material. If ﹩{\gamma }_{\infty }\sin i\lt 1﹩, then the observer lies below the emitting material. This geometric flip causes the polarization pattern to reflect across the image when ﹩{\gamma }_{\infty }\sin i﹩ crosses one, as shown in Figures 11 and 15.