A.5 Available marker symbols

The GNU libplot library supports a standard set of marker symbols, numbered 0...31. A marker symbol is a visual representation of a point. The libplot marker symbols are the symbols that the graph program will plot at each point of a dataset, if the ‘-S’ option is specified.

Like a text string, a marker symbol has a font size. In any output format, a marker symbol is guaranteed to be visible if its font size is sufficiently large. Marker symbol #0 is an exception to this: by convention, symbol #0 means no symbol at all. Marker symbols in the range 1...31 are defined as follows.

1. dot
2. plus (+)
3. asterisk (*)
4. circle
5. cross
6. square
7. triangle
8. diamond
9. star
10. inverted triangle
11. starburst
12. fancy plus
13. fancy cross
14. fancy square
15. fancy diamond
16. filled circle
17. filled square
18. filled triangle
19. filled diamond
20. filled inverted triangle
21. filled fancy square
22. filled fancy diamond
23. half filled circle
24. half filled square
25. half filled triangle
26. half filled diamond
27. half filled inverted triangle
28. half filled fancy square
29. half filled fancy diamond
30. octagon
31. filled octagon

The interpretation of marker symbols 1 through 5 is the same as in the well known Graphical Kernel System (GKS).

By convention, symbols 32 and up are interpreted as characters in a certain text font. For libplot, this is simply the current font. But for the graph program, it is the symbol font selected with the ‘--symbol-font-name’ option. By default, the symbol font is the ZapfDingbats font except in graph -T png, graph -T pnm, graph -T gif, graph -T pcl, graph -T hpgl and graph -T tek. Those variants of graph normally have no access to ZapfDingbats and other Postscript fonts, so they use the HersheySerif font instead.

Many of the characters in the ZapfDingbats font are suitable for use as marker symbols. For example, character #74 is the Texas star. Doing

     echo 0 0 1 2 2 1 3 2 4 0 | graph -T ps -m 0 -S 74 0.1 > plot.ps

will produce a Postscript plot consisting of five data points, not joined by line segments. Each data point will be marked by a Texas star, of a large font size (0.1 times the width of the plotting box).

If you are using graph -T pcl or graph -T hpgl and wish to use font characters as marker symbols, you should consider using the Wingdings font, which is available when producing PCL 5 or HP-GL/2 output. Doing

     echo 0 0 1 2 2 1 3 2 4 0 |
         graph -T pcl -m 0 --symbol-font Wingdings -S 181 0.1 > plot.pcl

will produce a PCL 5 plot that is similar to the preceding Postscript plot. The Wingdings font has the Texas star in location #181.