Geoid Height Calculation (HGEOID)
SGEOID, HGEOID, JHGEOID
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)