EGM2008 Earth Geoid
Geodynamics studies have an interest in the Earth’s geoid. The US National Geospatial-Intelligence Agency’s Office of Geomatics provide spherical harmonics models for the geopotential. The latest EGM2008 [Pavlis et al., 2012] geoid model is now available for remote use in GMT.
Usage
You access a global geoid grid by specifying the special name
@earth_geoid[_rru[_reg]]
The following codes for rru and the optional reg are supported (dimensions are listed for pixel-registered grids; gridline-registered grids increment dimensions by one):
Code
Dimensions
Reg
Size
Description
01d
360 x 180
g,p
98 KB
1 arc degree global EGM2008 geoid (1 min @ 315 km)
30m
720 x 360
g,p
320 KB
30 arc minute global EGM2008 geoid (1 min @ 157 km)
20m
1080 x 540
g,p
658 KB
20 arc minute global EGM2008 geoid (1 min @ 105 km)
15m
1440 x 720
g,p
1.1 MB
15 arc minute global EGM2008 geoid (1 min @ 79 km)
10m
2160 x 1080
g,p
2.3 MB
10 arc minute global EGM2008 geoid (1 min @ 52 km)
06m
3600 x 1800
g,p
5.9 MB
6 arc minute global EGM2008 geoid (1 min @ 32 km)
05m
4320 x 2160
g,p
8.0 MB
5 arc minute global EGM2008 geoid (1 min @ 26 km)
04m
5400 x 2700
g,p
11 MB
4 arc minute global EGM2008 geoid (1 min @ 21 km)
03m
7200 x 3600
g,p
20 MB
3 arc minute global EGM2008 geoid (1 min @ 16 km)
02m
10800 x 5400
g,p
34 MB
2 arc minute global EGM2008 geoid (1 min @ 11 km)
01m
21600 x 10800
g
100 MB
1 arc minute global EGM2008 geoid (1 min original)
Note that resolutions 05m and higher are tiled. See Remote Data Sets for more information.
See GMT remote dataset usage for when resolution codes are optional or required.
All of these data will, when downloaded, be placed in your ~/.gmt/server directory, with
the earth_geoid files being placed in an earth/earth_geoid sub-directory. If you do not
specify a CPT, the default CPT for this dataset (the GMT master turbo CPT) will be used.
Technical Information
We scale and reformat the original data to take up very little space so that downloads from the servers are as fast as possible. For the geoid grid this means we chose 0.01 m as the smallest data unit, which is well below the uncertainties in the model. Data are scaled and shifted to fit in a short integer grid that is highly compressed by netCDF lossless compression and chunking. The data are reported in meters.
Data References
Pavlis, N.K., Holmes, S.A., Kenyon, S.C. and Factor, J.K., 2012: [https://doi.org/10.1029/2011JB008916].