Matrix A, shown below, defines a perspectivity on the projectification of the euclidean plane. The axis of perspectivity is the x-axis. The center of perspectivity is on the y-axis at y = 1-k, and the homology coefficient of the perspectivity is k. The line parallel to the x-axis at y = 1 is mapped to the line at infinity. All the relevant definitions in the above statements are discussed in Perspectivity.html .