We observe that both camera centers C and C' ,the points x ,x' , and X are coplanar. This plane is the epipolar plane PI. The line that connects the two camera centers is called the baseline. The points E and E' where the baseline intersects the two views are called epipoles. The lines connecting x , E and X',E' are the epipolar lines. From the definition of perspective projection, we know that the points C,x , and X are collinear and that any point on this line between x and X projects as X in the first image. Therefore, we see that the correspondence of X must lie on the projection of the line from x to X in the second image. An illustration of epipolar geometry is shown in Fig. 2.