All GMT programs that accept table data input may read ASCII
or binary data. When using binary data the user must be aware
of the fact that GMT has no way of determining the actual
number of columns in the file. You must therefore pass that
information to GMT via the binary -bi[s]n option,
where n is the actual number of data columns (s
indicates single (4 bytes) rather than double (8 bytes) precision). If uppercase
S (or D) are used it implies that byte-swapping should be performed
just prior to writing (for output) or immediately after reading (for input).
Note that n may be larger than m, the number of
columns that the GMT program requires to do its task. If
n is not given then it defaults to m. If
n 
m an error is generated. For more information,
see Appendix B.