Problem with second axis in subplot

Question

Thomas Schaefer 2017-10-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/361670-problem-with-second-axis-in-subplot

编辑： Stephen23 2017-10-20

Hi all! I plot in a loop several graphs in the same subplot. Now I need a second x axis in the subplot.

figure(1)
HandleP1 = subplot(2, 2, 1, 'Parent', p);
hold on; 
plot(n, CH2VS)
ax1 = gca % current axes
ax1.Visible = 'off'; %just to see is the second axis is hidden anywhere
ac12 = axes('Position',ax1.Position,'XAxisLocation','top','YAxisLocation','right','Color','none');
ax12 = gca;
ax12.Visible = 'on';
ax12pos = ax1.Position;
ax12.XLim = ax1.XLim;

In my opinion, these few lines should do the trick, with the second x axis on top of the subplot. But the axis is simply not visible.

Whats wrong?

Best regards, Thomas

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Stephen23 2017-10-20

在 MATLAB Online 中打开

Thomas Schaefer's "Answer" moved here:

Hi!

I made a test file, to address the problem. And I think I know the problem, but not the solution. When I leave the figure as it is, the second x axis on subplot 1 is will be shown. If I make a uipanel from the figure, it is not shown.

    %%Test second x axis
clear all;
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
Fs = 10000;            % Sampling frequency                    
T = 1/Fs;             % Sampling period       
L = 5990;             % Length of signal
t = (0:L-1)*T;
n = 1:5990;
%%Initialize figure
fig1 = figure(1);
p = uipanel('Parent',fig1,'BorderType','none'); 
p.Title = sprintf('Figure 1, No second x axis in subplot 1 visible'); 
p.TitlePosition = 'centertop'; 
p.FontSize = 12;
p.FontWeight = 'bold';
out = 200*rand(1,5990);
ax1 = subplot(2,2,1, 'Parent', p) 
ax1_pos = ax1.Position; % position of first axes
ax12 = axes('Position',ax1.Position,...
    'XAxisLocation','top',...
    'YAxisLocation','right',...
    'Color','none');
ax12.XLim = [0, (L*T)];
ax12.XTick = 0:(1000*T):(L*T);
ax12.YTick = [];
%%figure 2
fig2 = figure(2);
out = 200*rand(1,5990);
ax1 = subplot(2,2,1); 
ax1_pos = ax1.Position; % position of first axes
ax12 = axes('Position',ax1.Position,...
    'XAxisLocation','top',...
    'YAxisLocation','right',...
    'Color','none');
ax12.XLim = [0, (L*T)];
ax12.XTick = 0:(1000*T):(L*T);
ax12.YTick = [];
currentFigure = gcf;
supertitle = get(currentFigure, 'Children');
title(supertitle, 'Figure 2');

So, the correct question is: Why is the second axis in a subplot in an uipanel not shown?

Best, Thomas

Thomas Schaefer 2017-10-20

在 MATLAB Online 中打开

Maybe there is a missunderstanding. I need the second x axis! But it is not shown, although I devined everything.

 Fs = 10000;            % Sampling frequency                    
T = 1/Fs;             % Sampling period       
L = 5990;             % Length of signal
t = (0:L-1)*T;
n = 1:5990;
 %%Initialize figure
fig1 = figure(1);
p = uipanel('Parent',fig1,'BorderType','none'); 
p.Title = sprintf('Figure 1, No second x axis in subplot 1 visible'); 
p.TitlePosition = 'centertop'; 
p.FontSize = 12;
p.FontWeight = 'bold';
 out = 200*rand(1,5990);
ax1 = subplot(2,2,1, 'Parent', p); 
 ax1_pos = ax1.Position; % position of first axes
ax12 = axes('Position',ax1.Position,...
    'XAxisLocation','top',...
    'YAxisLocation','right',...
    'Color','none');
ax12.XLim = [0, (L*T)];
ax12.XTick = 0:(1000*T):(L*T);
ax12.YTick = [];

Stephen23 2017-10-20

编辑：Stephen23 2017-10-20

在 MATLAB Online 中打开

As I wrote before, you need to specify the axes parent. Your code does not specify the axes parent, and so the second axes are created in the figure rather than in the uipanel. And thus the second axes are perfectly hidden under the uipanel, because you made them exactly the same size!

You need to do this:

axes(p, ...) % specify the parent as the first input argument!

instead of this:

axes(...)

which you are doing now. Have a look at your code where you create the axes.

Every time you create or access a graphics object you should always specify the handles explicitly. Do NOT rely on the current axes/figure/etc. as being the correct object that you need!

You did not specify the axes parent, and so it defaults to using the current figure as its parent.

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