  The geometry of a light wavefront evolving in the 3--space associated with a
post-Newtonian relativistic spacetime from a flat wavefront is studied
numerically by means of the ray tracing method. For a discretization of the
bidimensional wavefront the surface fitting technique is used to determine the
curvature of this surface at each vertex of the mesh. The relationship between
the curvature of a wavefront and the change of the arrival time at different
points on the Earth is also numerically discussed.
