Geodetic versus Geocentric Coordinates
---------------------------------------

All spherical rotations are applied to geocentric coordinates.
This means that incoming data points and grids are considered
to represent geodetic coordinates and must first
be converted to geocentric coordinates. Rotations are then applied, and the
final reconstructed points are converted back to geodetic
coordinates.  This default behavior can be bypassed if the
ellipsoid setting :ref:`PROJ_ELLIPSOID <Projection Parameters>`
is changed to Sphere.
