  We reveal a complete set of constraints that need to be imposed on a set of
3-by-3 matrices to ensure that the matrices represent genuine homographies
associated with multiple planes between two views. We also show how to exploit
the constraints to obtain more accurate estimates of homography matrices
between two views. Our study resolves a long-standing research question and
provides a fresh perspective and a more in-depth understanding of the multiple
homography estimation task.
