 outward surface normal at P.  For a point P
   off the spheroid, latitude is defined as the latitude of the
   nearest point to P on the spheroid.  Note if P is an interior
   point, for example, if P is at the center of the spheroid, there
   may not be a unique nearest point to P.

   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.  The sp