4.10 PostScript Features

PostScript is a command language for driving graphics devices such as laser printers. It is ASCII text which you can read and edit as you wish (assuming you have some knowledge of the syntax). We prefer this to binary metafile plot systems since such files cannot easily be modified after they have been created. GMT programs also write many comments to the plot file which make it easier for users to orient themselves should they need to edit the file (e.g., % Start of x-axis). All GMT programs create PostScript code by calling the pslib plot library (The user may call these functions from his/her own C or FORTRAN plot programs. See the manual pages for pslib syntax). Although GMT programs can create very individualized plot code, there will always be cases not covered by these programs. Some knowledge of PostScript will enable the user to add such features directly into the plot file. By default, GMT will produce freeform PostScript output with embedded printer directives. To produce Encapsulated PostScript (EPS) that can be imported into graphics programs such as IslandDraw and Adobe Illustrator for further embellishment, change the PAPER_MEDIA setting in the .gmtdefaults file. See Appendix C and the gmtdefaults man page for more details.