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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.
Next: B.1.2 Binary tables
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Paul Wessel
2004-10-01