FE 'tkGooie' Utilities


'PLOTtools' group



a GUI 'front-end' for 'gnuplot'

(FE = Freedom Environment)

FE Home Page > FE Downloads Page or FE Overview Page > FE 'tkGooies' Description Page >
FE 'tkGooies' 'PLOTtools' Page > This Log-Plot Page

INTRODUCTION to 'tkGnuplotXY_logORloglog_file2or3cols'

On a tkPiePlot page of this site, I describe a personal commitment to donate about five 'PlotQuik' utilities (Tk scripts) to the Tcl-Tk wiki at wiki.tcl.tk.

Since it may be late 2016 or 2017 or so before I get around to making some auto-plot-scaling and auto-ticmarking code in those scripts more robust (and modular), I have decided to make some Tk GUI 'front-ends' for the popular, widely-available 'gnuplot' program --- some plot utilities for

  1. XY plots of 2 or 3 columns of data from a text data file

  2. bar charts from a data file

  3. XY plots from math expressions of the form f(x)

  4. 3D surface plots from math expressions of the form g(x,y)

  5. and a few other 'gnuplot' front ends --- such as for making log and log-log plots.

Items 1, 2, 3, and 4 have been published at other web pages of this site. Those pages are accessible via the several links above.

I have written a Tk script for making log and log-log plots with gnuplot. That is the subject of this page. The code is presented further below.


I had some general goals for the Tcl-Tk 'front-end' script for this GUI. Those goals were shaped by the capabilities of the 'gnuplot' program.

As I proceeded in the coding and testing, my knowledge of the capabilities of 'gnuplot' advanced, and some of my goals were augmented or altered. Here are the main goals to which I gravitated.

  • Provide a row of buttons at the top of the GUI with labels such as 'Exit', 'Help', 'RePlot', and several color buttons to allow for setting some color options that are available with 'gnuplot'.

  • Provide an entry field for a file name --- and a 'GetFilename' button --- to use the Tcl-Tk 'tk_getOpenFile' utility to provide a way to navigate a directory structure to select a data file.

  • Provide 3 entry fields so that the user can tailor the plot title, and the x-axis and y-axis titles, as desired.

  • Provide 3 entry fields so that the user can specify, by integer number, the data columns of the file to be used for the x-values and a y1-plot --- and an optional y2-plot on the same graph.

  • Provide a checkbutton at the top of the GUI labelled something like 'Same Axis Units for Y1 and Y2' --- to, eventually, allow for the option to have a separate scale (min,max) for the Y2 data --- and, in that case, provide a y2-axis on the right side of the plot. But, for a first release, have that checkbutton set to 'Same Units' and grayed-out (disabled).

  • Provide several radiobuttons by which to specify whether the y-axis values, the x-axis values, or both are to be plotted in their logarithmic form. Since having the y-axis in lograrithmic form is the most common of the three, use that as the initial default.

    (For convenience in quickly comparing a log plot to a non-log plot, provide a 4th radiobutton with which to specify a 'no-log' plot.)

  • Provide 6 entry fields so that the user can specify min and max values for x, y1, and y2 --- with the min,max entry fields for y2 grayed-out (disabled), for now. So 4 of the min-max entry fields are enabled in the first release.

  • Provide 3 radiobuttons by which to specify which type of plot to render: lines-only, point-symbols-only, or both lines-and-points.

  • Provide an entry filed by which to specify the line width (1 to 6 pixels). Provide a couple of checkbuttons by which to ask for a border and/or a grid.

  • Provide radiobuttons for some of the output ('terminal type') options of 'gnuplot' --- GIF, PNG, JPEG, PS (Postscript), and SVG (Scalable Vector Graphics).

    In addition, provide a 'Test' button next to the radiobuttons, to take advantage of a 'gnuplot' ability to put out a 'test image' for any of the 'terminal types' --- showing the line-types and text orientation options and other options for the terminal type.

  • Provide 2 entry fields by which to specify the size of the image output (x-pixels, y-pixels).

  • Provide Y1 and Y2 entry fields by which to specify any of the 29 or so line types that 'gnuplot' provides.

  • Provide an X entry field, by which to specify a column of the file from which to fetch labels for the X axis tic-marks. Example labels: Oct2014, Nov2014, Dec2014, Jan2015, ..., Sep2015

  • Provide an option on the GUI, someday, to rotate the X and Y tic-labels by 90 degrees or some other angle like -45 degrees. 'gnuplot' supports this capability, for most of the 'terminal types'.


Like for some other Tk GUI scripts that I posted here, I made a 'text-sketch' for the GUI for this 'gnuplot' 'front-end' utility.

CONVENTIONS for the GUI 'text-sketch' below:

   * SQUARE-BRACKETS indicate a comment not to be included on the GUI.
   * BRACES indicate a Tk 'button' widget.
   * UNDERSCORES indicate a Tk 'entry' widget.
   * A COLON indicates that the text before the colon is on a 'label' widget.
   * CAPITAL-O indicates a Tk 'radiobutton' widget.
   * CAPITAL-X indicates a Tk 'checkbutton' widget.

              Gnuplot LOG or LOG-LOG plot of 2 or 3 columns from a data file:
              [window title]

  .fRbuttons  {Exit} {Help} {Plot} {Color of      {Color of  {Color of        X SameAxisUnits for Y1,Y2
                                    Lines}         axes}      background}

  .fRfile      Data Filename: _______________________________________________  {Browse...}

  .fRtitle     Plot title: _________________Plot title goes here._____________________________________________________

  .fRlogtype   Log axes:  O  x    O  y   O xy   O neither

  .fRxaxis     XColumn: 1__     XaxisMin ______  XaxisMax _______ XticLabelsCol#: __  _____X-axis label goes here____

  .fRy1axis    Y1Column: 2__    Y1axisMin ______ Y1axisMax _______ LineType(1-29): __  _____Y1-axis label goes here___

  .fRy2axis    Y2Column: ___    Y2axisMin ______ Y2axisMax _______ LineType(1-29): __  _____Y2-axis label goes here___

  .fRplotopts  PlotType: O Line  O Point  O Both     LineWidth(1-6): 1   X Grid?   X Border?

  .fRtics      XticLabelsAngle: ___  YticLabelsAngle: ___  X Minor Tics?

  .fRoutopts   Image file type: O GIF O PNG O JPG O PSc O PSbw O SVG O WXT {TestImg}  Xpixels: 800__   Ypixels: 600__  

  .fRmsg        [ ..........  Messages go here  ......................................................]

From the GUI 'sketch' above, it is seen that the GUI consists of about

  • 7 button widgets
  • 13 label widgets
  • 15 entry widgets (3 more could be added to specify tic-mark interval)
  • 12 radiobutton widgets in 3 groups
  • 4 checkbutton widgets
  • 0 scale widgets
  • 0 listbox widgets

Here is an image of the GUI that I ended up with for a 'first release'.

As I use this utility, I may find that I want to alter the GUI somewhat. If I make some significant changes, I intend to replace the script file here with the new file.

This GUI is not meant to be a toy or simply a demo. The LOG-plot of world population data shown (reduced) at the top of this page indicates that this Tk GUI is meant to be an actual 'productivity' tool --- a free and open-source one --- a tool that is open to enhancement and 'tweaking'.


In this example of world-population growth, note that a y-log plot of simple exponential growth would appear as a SINGLE STRAIGHT LINE angled upward in the plot.

However, this plot indicates that world-population growth exhibits a bi-exponential or tri-exponential growth pattern.

The graph is approximated pretty well by TWO straight lines --- one from year zero to about year 1800 --- and then, faster growth, from 1800 to 2000. The faster growth from about 1800 may be attributed to discoveries in microbiology thanks to the microscope and other new instruments and techniques --- in particular, discovery of bacterial and parasitic disease causes and discovery of ways to curb such diseases through better sanitation, better food preparation and storage, avoidance of risky situations, etc.

The graph may be approximated a little more accurately with THREE straight lines --- one from year zero to about year 1750 --- a second line from 1750 to about 1950 --- and a 3rd line from 1950 to 2000. The growth spurt after 1950 might be attributed to the discovery and widespread distribution of vaccines to combat diseases such as smallpox, polio, diptheria, whooping cough, tetanus, mumps, and measles --- and the roll-out of much better sewage, drainage, and water-treatment facilities and the ramped up manufacture and distribution of window and door screens and glass windows and doors.

Here is the original 600 x 400 pixels plot image for better examination. There are some dips in the 1300 to 1700 years that indicate the devastation caused by some plagues --- when large urban centers resulted in diseases spreading quite rapidly to large numbers of people when knowledge-of-cause (what to avoid) and effective-cures (for those already afflicted) were not available.

In summary, the log plot indicates some subtleties of the world-population data that is not apparent in a non-log plot.

Back to the code for this utility ...


Below is a link to the code that produced this GUI.

I follow my usual 'canonical' structure for Tk code, for this Tk script:

  0) Set general window & widget parms (win-name, win-position,
     win-color-scheme, fonts, widget-geometry-parms, win-size-control).

  1a) Define ALL frames and sub-frames.
  1b) Pack   ALL frames and sub-frames.

  2) Define & pack all widgets in the frames.

  3) Define keyboard or mouse/touchpad/touch-sensitive-screen
     action BINDINGS, if needed.

  4) Define PROCS, if needed.

  5) Additional GUI initialization (typically with one or more of
     the procs), if needed.

This Tk coding structure is discussed in more detail on the page A Canonical Structure for Tk Code --- and variations.

This makes it easy for me to find code sections --- while generating and testing Tk scripts, and when looking for code snippets to include in other Tk scripts (code re-use).

Experimenting with the GUI

As in all my scripts that use the 'pack' geometry manager (which is all of my 100-plus Tk scripts, so far), I provide the four main pack parameters --- '-side', '-anchor', '-fill', and '-expand' --- on all the 'pack' commands for the frames and widgets.

I think I have found a good setting of the '-side', '-anchor', '-fill', and '-expand' parameters on the 'pack' commands for the various widgets of this GUI. In particular ...

The filename, plot-title, axis-titles entry widgets expand/contract appropriately when the window size is changed --- and button and label widgets stay fixed in size and relative-location as the window size is changed. Entry fields for column-numbers, axis-limits, line-width/types, and pixel-sizes stay fixed in size.

If anyone wants to change the way the GUI configures itself as the main window size is changed, they can experiment with the '-side', '-anchor', '-fill', and '-expand' parameters on the 'pack' commands for the various widgets --- to get the widget behavior that they want.


Additional experimentation: You could change the fonts used for the various GUI widgets. For example, you could change '-weight' from 'bold' to 'normal' --- or '-slant' from 'roman' to 'italic'. Or change font families.

In fact, you may NEED to change the font families, because the families I used may not be available on your computer --- and the default font that the 'wish' interpreter chooses may not be very pleasing.

Furthermore, there are variables used to set geometry parameters of widgets --- parameters such as border-widths and padding. Feel free to experiment with those parameters as well.


Note that the 3 'Color' buttons call on an RGB color-selector-GUI script to set the colors.

You can make that color-selector script by cutting-and-pasting the code from the page offering 'a non-obfuscated color selector GUI', on this site.

Some features of the code

There are plenty of comments in the code to describe what most of the code-sections are doing.

See the 'PROCS' section of the code to see the code in all the procs that are used in this Tk script.

The main plotting code is in the proc 'replot'. See the comments in that proc for details on how the plotting is implemented by creating a 'gnuplot' script of commands to pass to the 'gnuplot' program.

Here is a list of the procs in this Tk script:


Although it sounds like stating the obvious, it is probably worth mentioning that the 'get_filename' proc is called by the 'GetFilename' button, and the 'replot' proc is called by the 'RePlot' button --- and the 'getset_color' proc is called by the 'Color' buttons.

The 'update_color_button' proc is called (once for each color button) near the bottom of the Tk script to initialize the GUI, after initializing some color variables. And the 'update_color_button' proc is also called in the 'getset_color' proc.

Just a few more comments on some 'features' of this script:

  1. ViewFile:

    After using a similar Tk 'gnuplot-frontend' utility on a few test files, I found that it would be handy to open the data file in a text file browser --- for example, in order to see the comments that I put at the top of a file, to help in setting titles --- or to see the data columns, to set min,max values for over-riding the default 'autoscale' functionality of 'gnuplot' (i.e. replace the asterisks in the min,max entries with numeric values).

    So I added a 'ViewFile' button to the GUI --- and the 'view_file' proc is called by that button. A 'TXTFILEviewer' variable can be used to set the text-file-viewer program to use. I have it set to use the FE 'xpg' utility.

    By the way, 'gnuplot' recognizes '#' as a comment line indicator in a data file. And 'gnuplot' allows you to change that indicator.

  2. EditInput:

    The 'edit_inputs' proc is called by the 'replot' proc to check the entries on the GUI --- that they are the proper numeric type, in the proper range, etc. If there is an exception, the 'popup_msgVarWithScroll' proc is used to popup a message to the user.

    The 'popup_msgVarWithScroll' proc is also called by the 'Help' button to show the text in the 'HELPtext' variable, which is set at the bottom of the script.

  3. Output Display:

    'gnuplot' typically renders the plot into an output file in a fraction of a second. Some 'viewer' variables are used in this Tk script to set the viewer program to use for the various output types. I have set variables as follows:

               set GIFviewer "/usr/bin/eog"
               set PNGviewer "/usr/bin/eog"
               set JPGviewer "/usr/bin/eog"
               set PSviewer "/usr/bin/evince"
               set SVGviewer "/usr/bin/inkscape"

    where 'eog' is the 'Eye of Gnome' image file viewer utility. 'evince' is a PDF and Postscript file viewer. Inkscape is an SVG editor. Inkscape is slow to open. It might be just as fast to use a web browser, like Firefox, as the SVG viewer.

It is my hope that the copious comments in the code will help Tcl-Tk coding 'newbies' get started in making GUI's like this.

Without the comments, potential young Tcler's might be easily frustrated and be tempted to return to their iPhones and iPads and iPods --- to watch how celebrities are mis-behaving --- while the really 'lasting', significant stuff is being done by inventors, researchers, engineers, scientists (physicists, chemists, biologists, etc.), architects, and millions of crafts-people and manufacturers, including carpenters, electricians, plumbers, iron-workers, bridge-builders, tunnel-builders, etc.

(Try the Science channel for some really interesting programming --- like the "How It's Made" and "How the Universe Works" and "Outrageous Acts of Science" series.)


Here is a link to CODE for the script 'tkGnuplotXY_logORloglog_file2or3cols.tk'.

And here is a link to a SAMPLE DATA file 'gnuplot_DATA_world_population.txt'.

I have most of the entry field variables set, in an 'Additional GUI Initialization' section near the bottom of the Tk script, to accomodate this test file when you first try this Tk GUI.

Other 'gnuplot' utilities

This is the fifth of several 'gnuplot front-end' utilities that I had planned to write. See the links to 4 others at the top of this page.

I still have a few more in mind. Other Tk 'gnuplot front-end' scripts that may follow are:

  1. MANY-LINES-with-LEGEND plot:
    a many-column xy-plot, created by selecting many columns of data, say, up to 10, from a text file containing columns of data --- with text-strings in the file containing names that can be used for a plot 'key' (legend) for the many lines on the plot.

  2. MAPS plot:
    a front-end to plot maps in 2D or 3D form, which 'gnuplot' is capable of doing.

  3. PIE plot:
    a front-end to do pie-plots, which 'gnuplot' was not originally designed to do, but which some people have accomplished with 'gnuplot'

Future Enhancements:

I have not tested this script extensively. No doubt, if I use it some more, I will find a few things to change, add, or fix.

I pointed out, above, that I may someday implement the 'Same Scale for Y1,Y2' checkbutton. In that case, if a user unchecks the button, several entry fields on the GUI would be changed from 'disabled' mode to 'enabled' mode. For example, the Y2 min,max entry fields and the Y2 axis label entry field.


I have provided for most of the 'gnuplot' 'terminal types' for output.

Note that I have provided for 2 types of Postcript output --- color and black-and-white. The 'PSc' option implements 'terminal postscript landscape color colortext'. The 'PSbw' option implements 'terminal postscript landscape mono blacktext'.

Furthermore, I have enabled the 'WXT' terminal type. The 'wxt' terminal uses the wxWidgets library, which is where the 'wx' comes from. The actual drawing is done via Cairo, a 2D graphics library, and Pango, a library for laying out and rendering text.

The 'wxt' terminal may offer the ability to get some high-quality output, because it may offer better quality lines and text (perhaps due to better anti-aliasing). However, the 'wxt' terminal does not write to an image file. The output is put in a terminal window. To get an image file, the user can use a screen-capture utility (such as 'gnome-screenshot' on Linux) to get the image in a PNG file. Then an image editor (such as 'mtpaint' on Linux) can be used to crop and resize the image file, if necessary. And a command like 'pngcrush -brute' can be used to minimize the size of the final PNG file.

At this time (2016 Feb), I do not plan to add anymore 'terminal types' to the GUI.

As I point out at the bottom of the 'HELPtext' for this Tk script, someday I may try to get more appealing plots --- with color gradient backgrounds and with 'shadow curves' and with 'ribbon curves' --- by using some of the 'gnuplot tricks' of Zoltan Voros, that can be seen at 'www.phyast.pitt.edu/~zov1/' in

If those pages are no longer available, you can see a couple of examples of that high-quality 'gnuplot' output at the bottom of a page on a Tk GUI Front-End for 'gnuplot' - for generating MATH EXPRESSION xy-plots - allowing for up to 3 math expressions on a plot.

By the way, here is the gnuplot script file that was created in one of my test runs.

    ! cd /tmp
    set terminal gif size 600 , 400  nocrop noenhanced butt xFFFFFF x000000 x000000
    set output '/tmp/userid_temp.gif'
    set title '      World Population (year 1 to 2000)'
    set timestamp '%Y %b %d %a %H:%M:%S'
    set xlabel '           Year'
    set ylabel '      World Population (millions)'
    set logscale y
    set xrange [ * : * ]
    set yrange [ * : * ]
    set xtics rotate by 0
    set ytics rotate by 0
    set xzeroaxis
    set yzeroaxis
    set border 15
    set nokey
    plot '...a filename goes here ...' using 1:2 with lines linewidth 1 linecolor rgb '#FF0000' linetype 1
    ! /usr/bin/eog  /tmp/userid_temp.gif &

The 'set logscale y' command is the command that is essential to this log-plot utility. It calls for a log-scale on the y-axis.

This is pretty crisp and clean, compared to all the comments that I have around the Tcl-Tk code that is writing out these gnuplot commands.

Note that by using the Tk GUI, the user can typically avoid having to page back and forth through 'gnuplot' documentation trying to find commands to use and the proper syntax for those commands --- and parameters to use with those commands.

And the user avoids many syntax errors, because I filtered out the errors that I made during testing, resulting in gnuplot commands that are probably going to work --- with gnuplot 4.2 and thereafter.

Essentially all of a user's documentation searching and syntax debugging is eliminated by use of this Tk GUI.

Thanks (again)

On many of my 'tkGooie' code donation pages, I have said ...

There's a lot to like about a utility that is 'free freedom' --- that is, no-cost and open-source so that you can modify/enhance/fix it without having to wait for someone else to do it for you (which may be never).

A BIG THANK YOU to Ousterhout for starting Tcl-Tk, and a BIG THANK YOU to the Tcl-Tk developers and maintainers who have kept the simply MAH-velous 'wish' interpreter going.

Bottom of the page for tkGnuplotXY_logORloglog_file2or3cols --- a plot utility in the FE 'tkGooies' system, in the 'PLOTtools' group.

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This code may someday be posted in a page on the Tcler's Wiki --- wiki.tcl.tk. If I do that, I will put a link to the page here.

This FE web page was created 2016 Feb 02.