B.1.1.2 Optional segment header records

When dealing with time- or (x,y)-series it is usually convenient to have each profile in separate files. However, this may sometimes prove impractical due to large numbers of profiles. An example is files of digitized lineations where the number of individual features may range into the thousands. One file per feature would in this case be unreasonable and furthermore clog up the directory. GMT provides a mechanism for keeping more than one profile in a file. Such files are called multiple segment files and are identical to the ones just outlined except that they have subheaders interspersed with data records that signal the start of a segment. The subheaders may be of any format, but all must have the same character in the first column. When using such files, you must specify the -M option. The unique character is by default '$>$', but you can override that by appending your chosen character to the M option. E.g., -MH will look for subheaders starting with H, whereas -M'*' will check for asterisks (The quotes are necessary since * has special meaning to UNIX). Some programs such as psxy will examine the subheaders to see if they contain -W and -G options for specifying pen and fill attributes for individual segments, -Z to change color via a cpt-file, or -L for label specifications. These settings (and occasionally others) will override the corresponding command line options.