Remote plotting via XTerm

Remote plotting via XTerm
=========================

One of the main features of UNIX systems is ability to work remotely.
Many of us have shell accounts at the SDF or elsewhere so it is not
necessary to explain the features of remote access.

I think that the most of people uses their remote shells for
console-oriented stuff like IRC, mail, git, text editors, off-line data
processing and so. But if one works with some data it is often useful
to be able to visualize them. The obvious way is to use X11 [1]. This
is of course possible but remote X11 connection is usually slow and
lagging when it is used via big networks. Then using of modern GUI
programs (based on the Gtk, for example) is usually a pain.

But in many cases a simple 2D graph is enough. And there is one
somewhat forgotten way how to visualize these things from remote
machines: the old good XTerm [2] can actually show simple graphics
elements. It can do because it can only work as a VT100 (or better)
emulator but it also can emulate the Tektronix 4014 graphical terminal.
The emulation might be limited but it is still enough to show black and
white lines and texts.

The XTerm has to be started with the "-t" parameter:

-------------------------------------
xterm -t
-------------------------------------

But how to generate such graphics? Some software offer direct output in
Tektronix format. The old UNIX command plot(1) [2] can do the same and
the graph(1) can prepare the graph data from text files. The modern
"plot" and "graph" implementations can be found in the GNU Plotutils
package [4].

To plot a simple graph on a Tektronix terminal one needs to prepare a
text file (say, "file.txt") with data (two colums, first is X value,
second is Y) and then to plot it:

-------------------------------------
cat file.txt |graph |plot -Ttek
-------------------------------------

And if one wants something more sophisticated then there is always the
Gnuplot [5]. It can use the "tek40xx" or the "vttek" terminals or a
terminal called "xterm". I recommend the later because it opens two
windows: the first is the usual XTerm (vt100 compatible) with the
Gnuplot command line and the second is a Tektronix-compatible window
for graphics. So one can work normally with the exception that the
graphics is only black and white.

And of course the GNU Octave often uses the Gnuplot for graphics so one
can benefit from this solution also when working with the Octave.

References:

[1] https://sdf.org/?tutorials/x11_forwarding
[2] http://invisible-island.net/xterm
[3] https://linux.die.net/man/1/plot
[4] https://www.gnu.org/software/plotutils/
[5] https://gnuplot.info