X: A 3D point projected to two cameras.u_i, u_j: Corresponding image points in the two views.The line joining the two camera centers and X forms the epipolar plane.The intersections of this plane with each image plane form epipolar lines.The key idea: the corresponding point must lie on the epipolar line.Essential Matrix 𝐸 \begin{equation}\mathbf{u}_j^\top\mathbf{E}\mathbf{u}_i=0\end{equation}..