matlab_graphics

matlab_graphics, a MATLAB code which illustrates how to achieve graphics effects.

I love MATLAB, I really do, but if the default behavior of MATLAB's graphic system doesn't work for you, it can be difficult to discover a technique for getting what you want - moreover, there rarely seems to be a sensible logical structure to explain what is going on, nor a systematic procedure for building an image.

Languages:

matlab_graphics is available in a MATLAB version.

Related Data and Programs:

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tri_surface_display, a MATLAB code which displays the 3D graphics information in a TRI_SURFACE file;

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triangulation_display, a MATLAB code which displays the nodes and elements of a triangulation on the MATLAB graphics screen;

triangulation_order1_display, a MATLAB code which plots piecewise constant data associated with a triangulation;

Source Code:

You plot a circle, and it comes out an ellipse. What is going on? Briefly, MATLAB uses a rectangle to display your plot. It takes the X and Y ranges of your data, and stretches them along the horizontal and vertical directions of the rectangle. This guarantees that a plot that is logically square will be displayed as a rectangle, and thus a circle becomes an ellipse. Luckily, the "axis equal" command helps. MATLAB still plots inside a rectangle, but now it stretches your X and Y data by the same single scale factor, resulting in some new white space to the left and right of your plot of a perfect circle.

• circle_test.m, a program that plots a circle twice, the second time using the "axis square" command.
• circle_test01.png, the first circle (which looks like an ellipse).
• circle_test02.png, the second version of the circle, which looks OK.

Surprisingly, a typical MATLAB plot can involve a lot of empty space. In the simple case where you are plotting a circle, you will get white space in the grid region itself if you enforce equal axis units, since MATLAB wants to display the grid within a rectangle. But you will also get a substantial margin of white space around the plot area itself. This can be annoying when you are trying to prepare graphics for use in a publication, or if you want to put several images side by side - the white space, which contains no information, eats up lots of space.

Can you cut back that white space? In particular, if you want to plot a circle (or anything else whose shape doesn't correspond to MATLAB's "golden rectangle"), can you make an image that is mathematically correct, and economic in terms of wasted white space?

You may try various combinations of "axis equal", "axis square", "axis tight", "axis ( [0,1,0,1] )" and so on, all the time coming halfway to your goal, without ever actually achieving an image that is square (or whatever aspect ratio you want), doesn't have wasted graph space, and doesn't have that excessive margin around the plot.

After wasting a lot of time, I stumbled across a few commands that, used together, seem to achieve the correct result. However, in my case, the image still looks rectangular in the MATLAB interactive viewer - but comes out nice and square in the PNG image rendered by the PRINT command.

Last revised on 30 May 2013.