line with a relativistic addition of velocity along the azimuthal angle gives an aberrated emission direction ${\bf{u'}}=(u'_x,u'_y,u'_z)$. The time of flight gives a change of the phase of the rotation of the star. Combining these two effects, and choosing $\Phi=0$ for radiation in the (x,z) plane from the center of the star, $\zeta$ and $\Phi$ are given by $\cos\zeta = u'_z$ and $\Phi =-\phi_{u'}-{\vec{r}}\cdot{\hat{u'}}$, where $\phi_{u'}$ is the azimuthal angle of $\hat{u'}$ and $\vec{r}$ is the emitting location in units of $R_L$. We project photon emissions on the ($\zeta$, $\Phi$) plane and observe the emission patterns on the sky. In ($\zeta$, $\Phi$) plane, the null surface can be determined easily because it consists of the points at which magnetic field lines are perpendicular to the rotation axis. For a field line, the null charge crossing is where the projected line crosses the equatorial line ($\zeta=90^{\circ}$). As an example, we show the projections of photon emission both outwards and inwards from one outer gap in ($\zeta$, $\Phi$) plane for the magnetic inclination angle ($\alpha=65^{\circ}$) in the upper panel of Figure 2, where the extension of the outer gaps on the $\phi$-direction is assumed to be $180^{\circ}$ and $(r_{lim}-r_{in})\sim 0.55R_L$(CRZ). As mentioned 