Last modified June 28, 2004 by Jim Hansen.

The location_mod.f90 for the annulus is a modified version
of ~/DART/location/threed_sphere/location_mod.f90.  The most
important thing to keep in mind in the annulus version is that
longitude actually mean azimuthal angle, and latitude actually
means radius.

The location_mod.f90 requires the parameters inner_rad (inner
radius of the annulus) and outer_rad (outer radius of the annulus)
from the input.nml.

Longitude (azimuthal angle) is in degrees, latitude (radius) is
in meters.
