Homepage of Stefan Salewski
Scaling axes in diagrams and data plots
When we try to write a program for plotting data or drawing diagrams, i.e. with GTK+/Cairo, a not always trivial task is to find a fine partition for the axes. In particular when the range of the data is not bound to a fixed range.
So I wrote a small function, which generates tic position and label values for arbitrary data ranges and a width number of desired tics/intervals. It is written in C language, but it should not be difficult to convert it to other programing languages. Of course, we may find a similar, maybe more sophisticated function in the famous gnuplot program.
The C source files are available in this directory for download:
This is the function header and some testing output:/* x1, x2: range to partition majors, minors: DESIRED! number of intervals==(tics-1). 1 <= majors <= 50, 1 <= minors <= 10. extend: if true, we may extend bounds with major tics, else only with subtics. array t holds position of tics. Its size should be at least 3*majors*minors. For major tics we may generate a string and write it at that position in diagram, for subtics we may print a |. return: total number of generated tics. */ int scaleaxis(double x1, double x2, int majors, int minors, int arraysize, bool extend, Tic t[]); stefan@AMD64X2 ~ $ cd AxisScale stefan@AMD64X2 ~/AxisScale $ gcc -lm -Wall AxisScale.c ASTest.c stefan@AMD64X2 ~/AxisScale $ ./a.out Scaling of axis in diagrams and data plots -- some examples: x1=-10 x2=90 majors=5 minors=5 extend=true |...|...|...|...|...|...| -20 0 20 40 60 80 100 x1=-1100 x2=90 majors=10 minors=10 extend=true |.........|.........|.........|.........|.........|.........|.........| -1200 -1000 -800 -600 -400 -200 0 200 x1=0 x2=100 majors=5 minors=5 extend=true |...|...|...|...|...| 0 20 40 60 80 100 x1=9 x2=106 majors=5 minors=5 extend=true |...|...|...|...|...|...| 0 20 40 60 80 100 120 x1=9 x2=106 majors=5 minors=5 extend=false ...|...|...|...|...|.. 20 40 60 80 100 x1=-2.1 x2=9.8 majors=6 minors=10 extend=true |.........|.........|.........|.........|.........|.........|.........| -4 -2 0 2 4 6 8 10 x1=-2.1 x2=9.8 majors=6 minors=10 extend=false .|.........|.........|.........|.........|.........|......... -2 0 2 4 6 8 x1=-117.2 x2=112.4 majors=10 minors=1 extend=true ||||||||||||| -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 x1=-1.172e+07 x2=1.124e+07 majors=10 minors=2 extend=true |.|.|.|.|.|.|.|.|.|.|.|.| -1.2e+07 -1e+07 -8e+06 -6e+06 -4e+06 -2e+06 0 2e+06 4e+06 6e+06 8e+06 1e+07 1.2e+07 x1=-0.001172 x2=0.001124 majors=6 minors=2 extend=false .|.|.|.|.|. -0.001 -0.0005 0 0.0005 0.001 x1=-117.2 x2=112.4 majors=10 minors=2 extend=true |.|.|.|.|.|.|.|.|.|.|.|.| -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 x1=-212 x2=-51.3 majors=3 minors=2 extend=false .|.|. -200 -100 x1=2.1 x2=9.8 majors=6 minors=10 extend=true |.........|.........|.........|.........| 2 4 6 8 10 x1=2.1 x2=9.8 majors=6 minors=10 extend=false |.........|.........|.........|......... 2 4 6 8 x1=-2.1 x2=9.8 majors=6 minors=10 extend=true |.........|.........|.........|.........|.........|.........|.........| -4 -2 0 2 4 6 8 10 x1=-2.1 x2=9.8 majors=6 minors=10 extend=false .|.........|.........|.........|.........|.........|......... -2 0 2 4 6 8 x1=-2.1 x2=-1.2 majors=6 minors=10 extend=false ......|.........|.........|.........|.........| -2 -1.8 -1.6 -1.4 -1.2 x1=-2.1 x2=-1.2 majors=6 minors=10 extend=true |.........|.........|.........|.........|.........| -2.2 -2 -1.8 -1.6 -1.4 -1.2 x1=-210000 x2=-120000 majors=6 minors=5 extend=true |...|...|...|...|...| -220000 -200000 -180000 -160000 -140000 -120000
This function is not much tested jet, but at least it may be a starting point for people who intend do develop plotting tools.