App Designer: Plotting on uiaxes from a callback. Formatting X-axis as HH:mm:ss

I have arrays of accelerometer sensor data which have been recorded at 10Hz. The array "time" contains time data as a sequence of seconds with 0.1s resolution: {1.1,1.2,1.3,1.4...etc}. I can plot my acceleration variables (Ax, Ay,Az) on the Y-axis against the X-axis timebase in seconds without a problem.

properties (Access = private)

time

Ax

Ay

Az

The data recordings are usually around 8 hrs long and I would like to format the x-axis in HH:mm.

After reading several helpful comments here, I supposed that app.graph_plot.XTickFormat = 'HH:mm'; but it doesn't work (the code jumps to the "catch" error handler). The only thing which I can get to slightly work is with "datetick".. however MATLAB gives me a warning that it is better to use "xtickformat".

app.CNS_plot = uifigure("Name",'Acceleration Plot','Color','white');

app.graph_plot = uiaxes(app.CNS_plot,'YLimMode','auto','YLim',[-inf,inf]);

app.graph_plot.Toolbar.Visible = 'on';

app.graph_plot.XAxis.Exponent = 0;

app.graph_plot.TickDir = 'out';

datetick(app.graph_plot,'x','HH:mm'); {Matlab warns me that this is not recommended}

app.graph_plot.XLabel.String = 'Time in Seconds';

When the figure is created, the X-axis is formatted as 00:00, 06:00, 12:00, 18:00 so it seems to work, however when I plot the data using

plot(app.graph_plot, app.time, app.Ax,"Color",'black','LineStyle','-','DisplayName','Accel X');

then all formatting disappears. Now I suppose that the issue could be with my "time" array definition. It is not explicitely defined as a 'datetime' or a 'duration' array. I am sure this must be a common problem, and all the answers I have seen so far (using XTickFormat) won't run.

Can anyone please suggest a solution?

many thanks

Answer 1

[Umar]

Hi @SteveM,

Thank you for your insightful comments regarding the x-axis time formatting issue.

After reviewing the MathWorks documentation, it’s clear that `xtickformat` works properly only when the x-axis data is a `duration` or `datetime` array. Since my `time` array is numeric (seconds), this explains why `app.graph_plot.XTickFormat = 'HH:mm';` fails and why formatting disappears after plotting.The recommended solution is to convert the numeric time to a `duration` type before plotting:

    time_dur = seconds(app.time);
    plot(app.graph_plot, time_dur, app.Ax, 'Color', 'black');
    xtickformat(app.graph_plot, 'hh:mm');

This approach avoids the deprecated `datetick` function and ensures the HH:mm formatting persists correctly.

Thanks again for your guidance. Let me know if this helped resolved your issue.

[SteveM]

Hi Umar,

yes you are right! I think I had come to the same conclusion as your answer arrived! I changed the arrays into "seconds" as you said and now the xtickformat operation works fine. Many thanks.

Steve