Geometry between the skewed disk plane and the equatorial plane of a black hole. The boundary of the disk is a ring, at which equal mass test particles are injected continuously. At the initial position, indicated by p, there are two orthonormal tetrads, i.e., {p, e_r,e_θ,e_φ} and {p, }. To compute the constants of motion, we need to transform the initial physical velocities of a particle , which are specified by {p, }, into {p, e_r,e_θ,e_φ}.