Loading computation.

   Displacements are computed in frequency domain. The original data are
   re-gridded to the uniform equiangular grid D2047 (4097x8192) with
   refined land-sea mask. The points of the ocean tides model that fall
   in land according to GTOPO30 are considered as land. The points of 
   the ocean tide model that fall in ocean according to GTOPO30 but 
   have the fill value (i.e. considered as land in odenan tide model) 
   are computed from adjacent points by interpolation with with 
   exponentially decaying weights.

   Then for every tide, cosine and sine components of ocean tide heights 
   is expanded into spherical harmonic of degree/order 2047. The harmonics
   are scaled by factors that depends on loading Love numbers. These scaled 
   spherical harmonics are used for computing 3D tidal displacement: 
   up, east, and north components. The up component is defined
   as a displacement towards direction orthogonal to the reference ellipsoid.

   Adopted density of sea water: 1025 kg/meter^3.

   The displacement is computed with respect to the center of the solid
   Earth's mass, excluding the mass of the ocean.

