I want to create printouts with exact sizes (1=1")

I somewhat frequently use Matlab to create images of things I want to build (as in build a physical object). In some situations, it would be useful to create a figure that's the exact size of the object I want to build. I can create, for example, a box that's 1x1 in the dimensions of my figure, but by the time I go through saving and then printing with all the attendant options, the "size" gets changed multiple times.

I'm about to write a function that creates a figure of a specified size and then exports that figure to a file and then print that file and then measure 1 unit with a ruler and then keep adjusting the parameters until I get it approximately right, but if there's a cleaner way to do it I'd like to hear it.

Answer 1

[Chunru]

g = figure;
g.Units = 'inches';
g.Position = [1 2 3  3];    % 3 by 3 inches
plot(rand(10,1));
saveas('test.pdf'); 
% You can measure the figure size in pdf to be the one you specified (outer
% box including the axis labels)

% If you want to set the axes size
%{
a = gca;
a.Units = "inches";
g.Position = [1 2 3  3];    % adjust these values
%}

[Lane]

Well, it produced a 2.34" square. There's definitely some scaling that goes on behind the scenes that makes Matlab's "inches" units worthless, so I guess I'll just keep iterating on the scale factor like my original plan.

[Chunru]

The square is the figure size which include the labelling text and so on.

If you do need the axes box to be 3 in by 3 in. Use the method mentioned in the comments section above or the following. You will have the axes box measured by 2"x2".

g = axes;
g.Units = 'inches';
g.Position = [1 1 2  2];    % 2 by 2 inches
plot(rand(10,1));
saveas(gcf, 'test.pdf'); 

[Stephen23]

"Well, it produced a 2.34" square."

Lets check your statement. I used the code from Chunru and added a background color to see the figure size:

g = figure();
g.Units = 'inches';
g.Position = [1 2 3  3];    % 3 by 3 inches
set(g,'InvertHardCopy','off'); % figure background color
g.Color  = [1,1,0];            % figure background color
plot(rand(10,1));
saveas(g,'bad4.pdf'); 

I then opened the PDF using Foxit Reader and used its inbuilt measuring tool:

I then opened the PDF using Inkscape and measured the size of the background object:

So I used two independent tools to confirm that Chunru's code works exactly as expected, and that your stament is incorrect: MATLAB did not perform any kind of scaling. Of course the axes do not have size 3" x 3", but because your question specifically asks to specify the size of the figure, the sizes of the axes are irrelevant.

"There's definitely some scaling that goes on behind the scenes that makes Matlab's "inches" units worthless"

Nope, as I demonstrated above, MATLAB has not scaled anything at all.

What is much more likely is that you are mixing up terms axes and figure. You will probably find this useful: https://www.mathworks.com/help/matlab/creating_plots/automatic-axes-resize.html

[Chunru]

hi @Stephen. Thanks for the clarificaiton. I did measure the size of figure and axes and confirmed that MATLAB produced right sized figures and axes.

[Lane]

You're not really suggesting that I was actually producing a 3" square and mismeasuring it as 2.34", are you?

The confusion was caused my me, I think, because when I said I wanted to create a "figure that's the exact size of the object I want to build" I wasn't confusing figures and axes, but I was using "figure" to mean "the paper version of the physical object I want to create". The problem is that almost every word I could use to describe that (including "object" for that matter) has a specific meaning in Matlab.

Anyway, Chunru's second variant (in which the printed graphics are the size of the real world) is exactly what I needed. Thanks.

[Lane]

Actually, there turned out to be one more step. Like I said in the original post, my goal was not to make the (matlab) figure or axes a certain size, but to make the actual plot units true to life. In Chunru's solution, the axes were indeed two inches, but those two inches contained 10 units and I needed them to contain two units (so one unit is one inch). I modified Chunru's code thusly:

figure(1); clf;
a = gca;
a.Units = "inches";
a.Position = [1 2 3 3];    
plot([0 3],[0 3])
axis tight
grid on
saveas(gcf,'~/test2.pdf');