4.2.2 Changing GMT Defaults

As mentioned, GMT programs will attempt to open a file named .gmtdefaults4. At times it may be desirable to override that default. There are several ways in which this can be accomplished.

1. Supply another filename using the +filename syntax, i.e., on the same command line as the GMT command we append the name of the alternate .gmtdefaults4 file with the plus sign as a prefix. Because any changes only apply to that one command you would have to append the alternate file to every command in your script. This is tedious but may be an option for situations when you cannot write in the current directory.
2. A perhaps less tedious method is to start each script by making a copy of the current .gmtdefaults4, then copy the desired .gmtdefaults4 file to the current directory, and finally undo the changes at the end of the script. Possible side effects include premature ending of the script due to user error or bugs which means the final resetting does not take place (unless you write your script very carefully.)
3. To permanently change some of the GMT parameters on the fly inside a script the gmtset utility can be used. E.g., to change the primary annotation font to 12 point Times-Bold we run
   

   gmtset ANNOT_FONT_PRIMARY Times-Bold ANNOT_FONT_SIZE_PRIMARY 12
   

   These changes will remain in effect until they are overridden.

4. Finally, if all you want to achieve is to change a few parameters during the execution of a single command but otherwise leave the environment intact, consider passing the parameter changes on the command line via the --PAR=value mechanism. For instance, to temporarily set the output format for floating points to have lots of decimals, say, for map projection coordinate output, append --D_FORMAT=%.12lg to the command in question.

In addition to those parameters that directly affect the plot there are numerous parameters than modify units, scales, etc. For a complete listing, see the gmtdefaults man pages. We suggest that you go through all the available parameters at least once so that you know what is available to change via one of the described mechanisms.

Figure 4.3: Even more GMT parameters that affect plot appearance.