ADOBE (Adobe's colorimage definition) [Default].
TILES (Plot image as many individual rectangles).
SEPARATION (Use 3 image calls for color separation).
The last method is only to be used to produce PostScript files for processing with the psto24 application; if submitted to other interpreters the job may crash. It is only intended as a way to create 24bit rasterimages from PostScript on Sun 8bit workstations.
0 Longitudes go from 0 to 360, latitudes from -90 to 90 [Default].
1 Longitudes go from -180 to 180, latitudes from -90 to 90.
2 Longitudes are unsigned 0 to 180, latitudes unsigned 0 to 90.
3 Same as 2, but with letters W, E, S, or N appended as appropriate.
4 Same as 0, but using decimal degrees instead of degrees, minutes, and seconds.
5 Same as 1, but using decimal degrees instead of degrees, minutes, and seconds.
WGS-84 1984 World Geodetic System
GRS-80 1980 International Geodetic Reference System
WGS-72 1972 World Geodetic System
Australian 1965 Used down under
Krasovsky 1940 Used in the Soviet Union
International 1924 Worldwide use
Hayford-1909 1909 Same as the International 1924
Clarke-1880 1880 Most of Africa, France
Clarke-1866 1866 North America, the Phillipines
Airy 1830 Great Britain
Bessel 1841 Central Europe, Chile, Indonesia
Everest 1830 India, Burma, Pakistan, Afghanistan, Thailand, etc.
Sphere 1980 The mean radius in GRS-80 (for spherical/plate tectonics applications)
Note that for some global projections, GMT may default to GRS-80 Sphere regardless of ellipsoid actually chosen. A warning will be given when this happens. If a different ellipsoid name than the ones mentioned here is given, GMT will attempt to open this name as a file and read the ellipsoid name, date, major axis (in m), minor axis (in m), and flattening from the first record, where the fields must be separated by white-space (not commas). This way a custom ellipsoid (e.g., those used for other planets) may be used.
gmtdefaults -D > ~/.gmtdefaults
You may now change the settings by editing this file using a text editor of your choice, or use gmtset to change specified parameters on the command line.