Recap of the hierarchy of each plot element

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Revision as of 03:32, 20 January 2013 by Sinanb (talk | contribs) (syntax highlighting.)
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Octave aims at being compatible with Matlab as much as possible, so the graphics part is very similar too to Matlab. In Octave the first choice to make is the graphics_toolkit(). Standard is the 'gnuplot' toolkit using the Gnuplot software package . The second choice is 'fltk'. You might want to try to test both of them for your plotting aims to see which solves your problem.

After the choice of the graphics_toolkit('gnuplot') or graphics_toolkit('fltk'), there is the following hierarchy to address when make/adapting your plot:

  • root (any hierarchy needs to start somewhere)
  • gcf () (the handle to your figure: one for every figure)
  • gca () (the handle to the axes inside a particular figure (several if you have subplots)
  • p = plot (x, y) (p is the handle (inside the current axes handle) to the data, data symbols, data line thickness, etc)
  • t = text (xlocation, ylocation, "some text") (t is the handle to the text and is a child of the current axes handle, like p)
  • pp = patch ([x1 x2 x3 x4], [y1 y2 y3 y4], "r") (pp is the handle to a red patch using the coordinates inside the current axes handle)

Let's do an example:

 graphics_toolkit ("gnuplot");
 x = 0:0.1:3;
 y = sin (x);
 p = plot (x, y, "b");

This should get you a plot of a part of a sine wave. Octave has used all standard properties like line widths, fonts, etc, except for the line color which was forced to be blue (via the 'b').

Before going into the hierarchy and how to change things, let's make things more complicated:

graphics_toolkit ("gnuplot");
figure (1)
x = 0:0.1:3;
y = sin (x);
p = plot (x, y, "b");
figure (2)
subplot (2, 1, 1);
r = plot (x, y.^2, "og");
subplot (2, 1, 2);
q = plot (x, x.^2, "k");
  • You now have 2 windows that popped up on your screen: figure 1 and figure 2.
  • figure 2 has two axes objects inside: a y = sin (x) .^2 and a y = x.^2.
  • the actual data and data-plot-properties are inside the handles p and r.

So let's say you want to change the line thickness of the data in the first figure:

figure (1)
set (p, "linewidth", 3)

You can get the color of the two other plots by referring to their handles:

get (q, "color")
get (r, "color")

Which will give you the RGB code for black (0,0,0) and green (0,1,0).

Have a look at all the things you can change with:

get (q)

And set anything that is not to your taste to something else (for what's available see the manual).

set (p, "marker", "*")

Adding text() inside an axes() object is done by

text (2, 0.8, "HERE");

... but it now is inserted in figure1, which might NOT be want you anticipated.

The text() command does not have the option to tell it in which figure or axes object to write the text. Make sure you have moved to current figure and axes before calling text() to insert text:

figure (2) % the following command will operate on figure(2)
get (gcf (),"children") % which two axes objects are there inside the current figure ?
set (gcf (), "currentaxes", (get (gcf (), "children"))(2)) % chose the second set of axes
text (1.0, 0.5, "THIS IS WHAT I WANTED")