EGM96 and EGM2008 and Other Geoid Grids
Geoid models created by NGA as a grid. These have the height above the ellipsoid in meters, and
should range up to approximately 100 m in absolute value.
EGM2008
EGM1996
-
Grid has 15 arc minute resolution
Using in MICRODEM
The grids are downloaded with the geology download, and then files will be in
available in C:\mapdata\geology\geology_grids
- Grid: EGM2008 can be used to do a vertical datum shift on the
edit menu.
- Point data base (such as ICEsat2): EGM2008 can be used to add a field VDATM_SHFT, Edit, Map coordinates.
You can then
- add to an elevation field in the database to get the geoid height if
you ellipsoid heights
- subtract from an elevation field in the database to find the
ellipsoid heights if you have geoid heights.
NAVD88 to other datums:
https://vdatum.noaa.gov/download.php#download_geoid has
GTX files
GEOID12B_CONUS
GEOID
18 US
GDAL reads a number of the grid shift files needed for the vertical datum
shifts:
- GTX
- NRCAN (Canada, but might have trouble with all the subsets)
- NTv2
References
Last revision 6/4/2020