The default UNIX plotting tools are pretty lame. The graph command has very limited control over data presentation, let alone annotation. Its companion, plot, supports a bevy of antique devices. I can't imagine using either tool for real work.

If your UNIX vendor provides Documenter's WorkBench (DWB), you also get grap, a pic preprocessor for drawing graphs. This is a real tool, but it is still severely limited. Fortunately, the freeware community has risen to the challenge. This column examines Geomview, GMT, Gnuplot, Graphics, and GRASS.

Geomview

Geomview is an interactive viewer for 3- and 4-D geometric objects. Based on OOGL, an object-oriented geometry library, it supports control panels, direct interaction, a large number of data types, and alternative spaces (for example, hyperbolic 3-space and Euclidean 4-space). It looks like a nifty tool for exploratory geometry and visualization. Sadly, it only runs on SGI Irises at present. Versions for NeXT and Sun are in the pipeline, however, so stay tuned.

Geomview can be found in ftp://geom.umn.edu/pub/software/geomview/. For more information on the package, contact the Geometry Center of the University of Minnesota (software@geom.umn.edu).

Generic Mapping Tools (GMT)

GMT is a very powerful batch-mode plotting package, with particular strengths in geographic applications. Its design borrows heavily from UNIX notions, and should seem familiar to UNIX-oriented scientists and programmers.

Small, specialized programs are used in combination to produce arbitrarily complex results. The programs (over 50 at this count) are written in C, and are normally used by means of shell scripts. For convenience, all GMT programs read default parameter settings from a "defaults" file, located in the current (or home) directory. They also "remember" parameters given in previous invocations. A shorthand syntax can be used to "recall" these in subsequent calls.

Most input and intermediate data are kept in ASCII form, for portability and readability. (2-D gridded data sets are kept in NCAR's binary netCDF format.) Graphical output files are written in PostScript, allowing a wide range of display devices.

The GMT-SYSTEM, distributed as seven megabytes of compressed archives, can be found in ftp://kiawe.soest.hawaii.edu/pub/gmt/. The software comes with a license agreement, designed for use by non-profit educational/research institutions and U.S. Government agencies. Other parties should contact Paul Wessel (wessel@soest.hawaii.edu). The Unidata network Common Data Form (netCDF) software can be found in ftp://unidata.ucar.edu/pub/netcdf/.

Gnuplot

Gnuplot is a command-driven interactive function and data plotting program. Surprisingly, it is not a product of the GNU Project, just a happy coincidence in the freeware name space. This C program accepts function descriptions in a superset of C syntax. It provides a variety of scaling and labeling options, and supports dozens of output devices, including LaTeX pictures.

Gnuplot is archived in ftp://ftp.cs.dartmouth.edu/pub/gnuplot/. Many authors have worked on Gnuplot, and it is still supported by an active community. To join the Gnuplot mailing list, send a note to info-gnuplot-request@dartmouth.edu. Even better, read the equivalent newsgroup comp.graphics.gnuplot.

GRASS

The Geographic Resources Analysis Support System (GRASS) combines a raster geographical information system (GIS), a vector GIS, an image processing system, and a graphics production system. Consequently, it is fairly large; the compressed archives take up more than 15 MB.

With nearly 200 programs and 300,000 lines of code, GRASS is not a system to approach casually. It requires a substantial investment of time, but repays this with a broad range of capabilities. It isn't for everyone, but any individual or institution who is interested in large-scale analysis of data should give GRASS a serious look.

More generally, GRASS is an excellent (award-winning!) example of properly handled government freeware. The software is developed by and for the government, with coordination provided by an inter-agency steering committee. GRASS is very actively supported, with annual user meetings, classes, distribution centers, educational materials, email lists, a newsletter, and videotapes.

GRASS has a diverse user community. Federal agencies account for 40% of the users. Private firms and educational institutions each take up another 25%. The remaining 10% is split among domestic and foreign governmental bodies. GRASS is in the public domain; public distribution and use is encouraged. The official GRASS archive is ftp://moon.cecer.army.mil/grass/. Contact the Grass Information Center: gic@zorro.cecer.army.mil or +1 800-872-2375x220 (+1 800-252-7122x220 inside Illinois) for more information.