The plotutils Package

 [image of the Head of a GNU]

The GNU plotutils package contains software for both programmers and technical users. Its centerpiece is libplot, a powerful C/C++ function library for exporting 2-D vector graphics in many file formats, both vector and bitmap. On the X Window System, it can also do 2-D vector graphics animations.

libplot is device-independent, in the sense that its API (application programming interface) does not depend on the type of graphics file to be exported. A Postscript-like API is used both for file export and for graphics animations. A libplot programmer needs to learn only one API: not the details of many graphics file formats.

The package also contains command-line programs for plotting scientific data, such as GNU graph for XY plotting. Many of them use libplot to export graphics. So, they can export graphics in any of libplot's supported formats, such as

The current version of the plotutils package is 2.6, released September 2009. It can be installed on GNU/Linux, FreeBSD, and Unix systems.

The plotutils package comes with a 185-page manual. Here is an English-language version of the manual, and here is a Japanese-language version of the manual. People working through the many examples given in the manual should look at the expected output (PDF). (Thanks to Daisuke TOMINAGA for the last two items!).

The package is free software. Its source code is distributed as a 3.7 megabyte gzipped tar file. Here is how you can get it.

What command-line programs does the package contain?

It includes

We developed these command-line programs to replace the Unix command-line programs graph, plot, and spline. The GNU versions are far more powerful, and are free software.

What graphics library does the package contain?

GNU libplot, a C/C++ function library for device-independent 2-D vector graphics. GNU libplot is compatible with the traditional Unix libplot library, but is far more powerful. It is installed as part of the package. On systems that support shared libraries, it is installed as a shared library. A C++ class library called libplotter, which provides an object-oriented interface to libplot's functionality, is optionally installed as well.

GNU libplot and libplotter support all the output formats mentioned above (X11, SVG, PNG, PNM format, pseudo-GIF, WebCGM, Illustrator format, idraw-editable Postscript, PCL 5, Fig format, HP-GL/2, ReGIS, Tektronix, and GNU Metafile). They can produce animated pseudo-GIFs, and smooth, double-buffered animations on any X Window System display. The libplot imaging model is similar to Postscript's. In any output format, they can draw the following.

When using libplot or libplotter, a programmer draws vector graphics in a `user frame', rather than in the device frame. As in Postscript, the user frame may be transformed into the device frame by an arbitrary affine map. Scaling, rotation, shearing, and translation are all supported.

Does the package really produce GIF files?

Even though the plotutils package can produce what appear to be GIFs and animated GIFs, it does not transgress any patents covering the LZW compression algorithm. The reason is that instead of LZW encoding, it uses run-length encoding, which is not patentable. To avoid confusion, we call the files produced by the package `pseudo-GIF files'.

What related software is available elsewhere?

A simple piechart plotting program that illustrates the use of GNU libplot is available here. It was contributed by Bernhard Reiter. Chris Elliott has developed a libplot-based program called ascii_chart, which takes data in a two-column format and prepares a piechart plot or a line plot.

There is a Python wrapper for libplot, and a SWIG wrapper too. libplot drawing functions can also be used from a Perl module (Graphics::Libplot).

Who developed the plotutils package?

The two primary authors of the plotutils package are Robert Maier and Nick Tufillaro (who developed ode). Many other people have also contributed. The rasterization code used by the export filters, which is distributed as a separate package, is based on the scan-conversion code in the sample X Window System server.

Visit the Free Software Directory's Science section for more utilities and related software.