GMT is a program useful for mapping. it has a set of 60 tools for manipulating geographic and Cartesian data sets.It is able to produce encapsulated Postscript file (EPS).The kind of figure that is capable of plot range from a simple x-y plots until illuminated surfaces and 3D perspective views.
Ploting A simple mapA common way of usign GMT is by inputing the commands through a terminal window(using cygwin for example) Let's see a simple example Suppose that you want to do a map of your country the way you could do this is using the next commands pscoast -Rxmin/xmax/ymin/ymax -Jproyection -GR/G/B -SR/G/B -Dquality > outputfilename pscoast -R272/278/10/15.5 -JM15c -Ba2g2 -G245/245/200 -S140/170/235 -Lf273/10.5/10.5/100 -Dh -N1 -W1 -P -K >outputfile1.ps
Figure 1. A simple map plot. GMT has many useful tools, one of them is the psmeca.The function of this command is to plot focal mechanism. you can get focal mechanism data from http://www.globalcmt.org/CMTsearch.html
Ploting Focal mechanism
There you should specify the date and the output file type that you select should be psmeca input. the common parameters of the psmeca command are as follows psmeca inputfilename -Rregion -Jproyection -GR/G/B -Smxc(size of the symbol in centimeters or inches) -Pfor portrait> outputfile2.ps for example using the previous example pscoast -R272/278/10/15.5 -JM15c -Ba2g2 -G245/245/200 -S140/170/235 -Dh -Lf273/10.5/10.5/100 -Dh -N1 -W1 -P -K >gmt2.ps psmeca 2005cmt.gmt -R -JM -Sm0.5c/-1 -G0/0/255 -P -O -K>>gmt2.ps pstext -R -JM -P -O -K <
> gmt2.ps 274.2 13 18 0 1 LT Nicaragua EOF Here is the script for figure 2 focal mechanims
Figure 2. Focal mechanisms.As you can see the text was added by using the "pstext" command.
Relief like plotsSo far just "plane" have we seen.As mentioned before GMT is capable of produce relief like plots. For making a relief like map, it is important to have topographic data. a site where you can download it is http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.htmlHere is the script for figure 3 USrelief
This data "GTOPO30" are DEM type data so you must converted to GMT type before you proceed. Here is a shell script DEM2xyz After you have this data in xyz you should make a grid. This can be done by using the GMT command xyz2grd as follows xyz2grd inputfilename -Rregion -Idivision of the grid -Goutputfile0.grd -N-9999 -Vverbose mode to be able to know what GMT is doing. Once we have converted the xyz data to grid we can make a illumination file for helping enhance our map, for this purpose we use the grdgradient command grdgradient inputfilename.grd -Ne.8(a function wich varies from 0 to 1 normalizes using a cumulative Laplace distribution) -AAzimuthal direction for a directional derivative -Munits -Goutputfilename.grd for example grdgradient us.grd -Ne.8 -A100 -M -Gus_i.grd>gmt3.ps and the next step is ploting all the previous results. Using grdimage command grdimage us.grd -JM6i -P -B2 -Ctopo1.cpt -V -K -Ius_i.grd > gmt3.ps psscale -D3i/8.5i/5i/.25ih -Ctopo1.cpt -I0.4 -B/:m: -O >> gmt3.ps The last command(psscale)plot a color scale of the different elevations in the map
Figure 3. Relief like map. Figure 4. Relief like map.Here is the script for figure 4 NICrelief
Again,for making a perspective like map, it is important to have topographic data. Another site where you can download it is http://srtm.csi.cgiar.org/
Finally a more realistic map could be do it by using the command grdview grdview inputfilename.grd -Jprojection -Eview_Az/view_el -Qtype -I1intesitygrid.grid -Ccolor palette -Vverbose mode -Bmap boundary annotations and tickmark intervals5 -JZsets the vertical scaling>gmt4.ps grdview 06.grd -JM12i -E272/10 -Qi50 -I18i.grd -Ctopo.cpt -V -B5 -JZ0.5i>gmt4.ps
Figure 5. Perspective of a set of data gridded.Of course the quality of the image will depend on the quality of the topographic data