  In general it requires at least 7 point correspondences to compute the
fundamental matrix between views. We use the cross ratio invariance between
corresponding epipolar lines, stemming from epipolar line homography, to derive
a simple formulation for the relationship between epipoles and corresponding
points. We show how it can be used to reduce the number of required points for
the epipolar geometry when some information about the epipoles is available and
demonstrate this with a buddy search app.
