Geoid Height Calculation (HGEOID)

NAME
    sgeoid - Select geoid model by its name.
             [National Geospatial-Intelligence Agency (USA) "NGA" model is
              available at present with mesh resoluion of 1 min.Lat. and 1.5
              min.Long.]
             [Global but lower resolution model is available by the name ".",
              at the resolution of 10 min.Lat. x 15 min.Long.]
             Before this routine is called, the NGA model is the default.
    hgeoid / jhgeoid -
             Calculate Geoid height for the position as a linear interpolation
             of model data.
             (Higher resolution data is prepared only for the range of
              20-50 deg.N and 120-150 deg.E, for "NGA" model.  The user may
              bring in another model data with the form of Standard GRID data
              of each 1 deg.Lat. x 1 deg.Long. area.)
 (Note 1) The NGA regional data used for the calculation are stored under the
    directory /home/SHARE/date/geoid/NGA/, with a subdirectory tree for each
    UTM zone (e.g. Z53).  For instance, "Z53/N35E137.hgeoid" file includes
    the mesh data for a [1 deg.Lat. x 1 deg.Long.] range, SW corner of which
    is 35 deg.N Lat., 137 deg.E Long., in a form of Standard GRID data of
    coordinate number 199.
      Users may place their own model data in /home/SHARE/date/geoid/Name/ with
    the simillar way, in order to use it as model name of Name.
    [For southern hemisphere N?? may be alternated by S?? (south latitude),
    and also E### by W### (west longitude) for western hemisphere (still
    corresponding to SE corner of the range).]
 (Note 2) The worldwide geoid data are stored with a similar format in the
    /home/SHARE/data/geoid/world.hgeoid file, and consist of 1081*1441 values
    corresponding to 10min.Lat. by 15min.Long. mesh.
      The program only selects an appropriate set of data and executes a
    linear interpolation.

SYNOPSIS

      call sgeoid(model)
  model       [char]   Geoid model name [20 bytes at most].
          The model name is same as the name of subdirectory including data.

      hg = hgeoid(flat, flon)
  flat, flon  [float]  WGS Lat. and Lon. (in minutes) of the calc. point.
  hg          [float]  Calculated results. Geoid height (in meters) is given.
          If the model does not yield valid data, subprogram will error exit.

      k = jhgeoid(flat, flon, hg)
  flat, flon  [float]  WGS Lat. and Lon. (in minutes) of the calc. point.
  k           [int]    Flag whether valid data is obtained (=0), or not.
  hg          [float]  Calculated results if k=0.
                        Geoid height (in meters) is given.
          If the model does not yield valid data,
           subprogram will return k=2, and hg=0.

SUPPLEMENT
   The "NGA" model data above is prepared in use of the geoid model "EGM2008"
  by the National Geospatial-Intelligence Agency (USA).
  (http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008/egm08_wgs84.html)