[Proj] GeographicLib geoid calculations

[support.mn at elisanet.fi]

Paul,

it says:

"egm96.c 	 997 	 22 months 	 paul 	 Improved documentation for "standalone" UTM and EGM96 conversion functions
egm96.dat 	 466 	 2 years 	 paul 	 Add WGS84 --> EGM96 conversion functionality. Not well tested yet. "

"NOT WELL TESTED YET!"

regards: Janne.

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Paul Kelly [paul-grass at stjohnspoint.co.uk] kirjoitti: 
> Charles Karney wrote:
> > 
> > GeographicLib uses 2 bytes per grid point to store the data (vs 4 bytes
> > per grid point for most other implementation) and, by default, does not
> > read the entire table into memory.
> 
> While not as polished as the very impressive GeographicLib, I thought it 
> was worth pointing out that an implementation I wrote a couple of years 
> ago in C has similar properties (2 bytes per grid point, and 
> user-specifiable how much of the grid to load into memory). It uses the 
> cubic convolution interpolation method proposed by Keys in 1981. Some 
> details here:
> 
> <https://haptimap.ee.qub.ac.uk/doc/group__standalone__gps.html>
> (look at the egm96_* functions) and source code as well as binary grid 
> file available here:
> 
> <https://haptimap.ee.qub.ac.uk/viewvc/haptimap/trunk/plugins/>
> 
> The software may be distributed under the LGPL license, although I have 
> to admit this isn't at all clear from the above links...
> 
> > (Incidentally, GeographlicLib lets you work directly with the spherical
> > harmonic expansions of the geoid models using the Gravity class.  So you
> > can construct grids for any of EGM84, EGM96, or EGM2008 at any
> > resolution.)
> 
> Again, not so elegant (requires manual pre-processing with no nice API, 
> but maybe still useful for an embedded application) - grids of any size 
> at various resolutions may be created using the software here (slightly 
> modified version of C code by D. Ineiv from 2006):
> 
> <https://haptimap.ee.qub.ac.uk/viewvc/haptimap/trunk/external/egm96/>
> 
> Just in case it is useful to anybody!
> 
> Best regards,
> 
> Paul
> 
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