 matrix
   equation:

                  t          |                                  t
      (dx, dy, dz)   = jacobi|              * (dlon, dlat, dalt)
                             |(lon,lat,alt)


   This routine computes the matrix

            |
      jacobi|
            |(lon,lat,alt)


   In the planetographic coordinate system, longitude is defined
   using the spin sense of the body.  Longitude is positive to the
   west if the spin is prograde and positive to the east if the spin
   is retrograde. 