with one of the boundary FOV vectors.
                 ./
                 SpiceDouble             lat;
                 SpiceDouble             lon;

                 /.
                 The variable `pmgsmr' is the opposite of the apparent
                 position of Mars with respect to MGS.
                 ./
                 SpiceDouble             pmgsmr [3];

                 /.
                 The variable `radii' is a vector of the semi-axes of Mars.
                 ./
                 SpiceDou