How to draw a "xline" with a given height for the line and a given vertical position for the text?

How to draw a xline with a given height for the line and a given vertical position for the text?

In other words, I need a shorter xline and I want to decide exactly how short that line will be.

Also, I would like to customise more the vertical position of the text, i.e. putting it a bit higher or a bit lower than what given by 'LabelVerticalAlignment'.

Answer 1

[Star Strider]

The xline function by default goes to the limits if the y-axis. The label only has limited options for positioning.

It will likely be easier to create a single vertical line and attach a text object to it:

x = 1:0.1:10;
y = sin(2*pi*x/5);

figure
plot(x, y)
[xl,xt] = xlin(7,'Message', 0.1,  0.8, 0.25);
grid

function [hl,ht] = xlin(x,txt,ylo,yhi,ytxt) 
% Documentation: 
%   x       = x-Position
%   txt     = Text String
%   ylo     = Low y-Value (Start)
%   yhi     = High y-Value (End)
%   ytxt    = Text Starting Position
hold on
hl = plot([x x],[ylo yhi],'DisplayName',txt, 'LineWidth',1);
ht = text(x,ytxt, txt, 'Horiz','left', 'Vert','top', 'Rotation',90);
hold off
end

Returning the ‘hl’ and ‘ht’ handles permits easily changing certain attributes of the line and text objects without changing the function.

.

[Sim]

Thanks a lot, exactly what I needed!!! :)

[Star Strider]

As always, my pleasure!

Answer 2

[Voss]

Here's how you can specify the Vertical and Horizontal Alignment of the xline's label:

warning off all
figure();
xline(1,'_','Line at x = 1','LabelVerticalAlignment','top');
xline(2,'_','Line at x = 2','LabelVerticalAlignment','bottom');
xline(3,'-','Line at x = 3','LabelVerticalAlignment','middle');
xlim([0 4]);

figure();
xline(1,'_','Line at x = 1','LabelHorizontalAlignment','left');
xline(2,'_','Line at x = 2','LabelHorizontalAlignment','right');
xline(3,'_','Line at x = 3','LabelHorizontalAlignment','center');
xlim([0 4]);

If you don't want the xline itself to span the y-limits of the axes, i.e., have an xline of a given height, and/or have more control over where the label is, then you're better off creating a regular line (not an xline) and a text label separately:

figure();
line([1 1],[0 4],'Color','k');
text(1,1.5,'Line at x = 1','Rotation',90,'VerticalAlignment','bottom','HorizontalAlignment','center');
ylim([0 6]);

[Sim]

Thanks a lot, very nice answer @_! I would accept both your solution and the @Star Strider's one.... I will go with the @Star Strider's one just because it is slightly more compact... but basically they are very similar.....!!! Many many thanks!!

[Voss]

You're welcome!

Note that it is more efficient to use the low-level function line() than the high-level function plot(), and that plot() can potentially do unwanted things to your axes (or objects in it) that line() will not do. Therefore, I think it is better to use line() for this purpose.

[Sim]

Ah ok, I did not know it....... Can I accept both answers?? I would like to... :-)

Answer 3

[Walid]

Please check ConstantLine Properties (frome MATLAB R2021a):

you must use: xline(5,'LabelHorizontalAlignment',''left'') and likewise LabelVerticalAlignment for top, middle or button of the xline.

[Sim]

Thanks @Walid... I am already using those properties.... But, I need to customise them with precise/given heights/positions (not just the usual 'left','right','up','down',...)