Developing Unmanned Aerial Vehicles (UAV) with self-stabilization capabilities represents an intensive research field nowadays. This paper aims to show that combining our previous horizon extraction algorithm with homography methods permits to estimate the homography more robustly and thus the UAV attitude. We show that imposing horizon constraint permits to remove evident inconvenient non-planar points. Moreover, we explain that computing the horizon in the sphere permits to compute the normal vector of the ground plane and thus retrieve the right motion among the four possible solutions obtained by planar homography, which is not a trivial problem usually.