The models where I'm going to trace rays consist of homogeneous transversely isotropic layers with dipping interfaces which are not allowed to cross in the area of interest. Each layer is defined by the intersects and dips of the boundaries, the five elastic constants that define a transversely isotropic medium and the orientation of the axis of symmetry with respect to the vertical. If the anisotropy is elliptical, only the velocities parallel and perpendicular to the axis of symmetry are required, as explained in Michelena (1992).