gnuplot documentation

60 PLOT gnuplot 4.3 67
The keyword filetype in controls the routine used to read the file, i.e., the format of the
data. For a list of the supported file types, type show datafile binary filetypes. If no file type is
given, the rule is that traditional gnuplot binary is assumed for splot if the binary keyword stands
alone. In all other circumstances, for plot or when one of the keywords appears, a raw
binary file is assumed whereby the keywords specify the binary format.
General binary data files fall into two basic classes, and some files may be of both classes depending upon
how they are treated. There is that class for which uniform sampling is assumed and point coordinates
must be generated. This is the class for which full control via the keywords applies. For
this class, the settings precedence is that command line parameters override in-file parameters, which
override default settings. The other class is that set of files for which coordinate information is contained
within the file or there is possibly a non-uniform sampling such as gnuplot binary.
Other than for the unique data files such as gnuplot binary, one should think of binary data as conceptually
the same as ASCII data. Each point has columns of information which are selected via the associated with using. When no format string is specified, gnuplot will retrieve a number of
binary variables equal to the largest column given in the . For example, using 1:3 will
result in three columns being read, of which the second will be ignored. There are default using lists
based upon the typical number of parameters associated with a certain plot type. For example, with
image has a default of using 1, while with rgbimage has a default of using 1:2:3. Note that the
special characters for using representing point/line/index generally should not be used for binary data.
There are keywords in that control this.
60.2.2.1 Array Describes the sampling array dimensions associated with the binary file. The coordinates
will be generated by gnuplot. A number must be specified for each dimension, thereby calling
out the size of the array. For example, array=10x20 means the underlying sampling structure is twodimensional
with 10 points along the first (x) dimension and 20 points along the second (y) dimension.
A special "number", Inf, can be used to indicate that data should be read until the end of file. A colon
can be used to separate the dimensions for multiple records. For example, array=25:35 indicates there
are two one-dimensional records within the file. The colon behavior applies to the remaining keywords
in this list for which it makes sense to be associated with individual records.
Currently, syntax allows for up to three-dimensional arrays. However, no conventions have yet been
made for handling three-dimensional coordinates.
60.2.2.2 Record This keyword serves the same function as array, having the same syntax. However,
record causes gnuplot to not generate coordinate information. This is for the case where such
information may be included in one of the columns of the binary data file.
60.2.2.3 Format The default binary format is a float. For more flexibility, the format can include
details about variable sizes. For example, format="%uchar%int%float" associates an unsigned character
with the first using column, an int with the second column and a float with the third column. If
the number of size specifications is less than the greatest column number, the size is implicitly taken to
be similar to the last given variable size.
Furthermore, the format specification can include "discarded" terms via the * character. For example, to
skip the middle column of the previous example, one could write format="%uchar%*int%float" and
gnuplot will discard the middle integer. To list variable sizes, type show datafile binary datasizes.
There are a group of names that are machine dependent along with their sizes in bytes for the particular
compilation. There is also a group of names which attempt to be machine independent.
60.2.2.4 Endian Often the endianess of binary data in the file does not agree with the endianess
used by the platform on which gnuplot is running. Several words can direct gnuplot how to arrange
bytes. For example endian=little means treat the binary file as having byte significance from least to
greatest. The options are
little:
big:
least significant to greatest significance
greatest significance to least significance