on of an object in the
   planetographic coordinate system.  However, when performing
   vector computations it's hard to beat rectangular coordinates.

   To transform states given with respect to planetographic
   coordinates to states with respect to rectangular coordinates,
   one makes use of the Jacobian of the transformation between the
   two systems.

   Given a state in planetographic coordinates

      ( lon, lat, alt, dlon, dlat, dalt )

   the velocity in rectangular coordinates is given by the