converting indices into time

Hi,

I have attached my Matlab graph. I have 163000 indices for speed and sampling rate was 3000. I would like to convert the x-axis into time so it will be around 54 seconds.

could anyone help? thanks.

openfig figure1

ans = 
  Figure (1) with properties:

      Number: 1
        Name: ''
       Color: [1 1 1]
    Position: [314 365 1184 495]
       Units: 'pixels'

  Show all properties

Answer 1

[Star Strider]

Try this —

F = openfig('figure1.fig');
Lines = findobj(F, 'Type','line');
tidx = Lines.XData;
speed = Lines.YData;
Fs = 3E+3;                                              % Sampling Frequency (Hz)
tsec = tidx/Fs;
Lines.XData = tsec;                                     % Set X-Axis To 'tsec'

Check = tsec(end)

Check = 54.3333

EDIT — (20 Jul 2023 at 10:47)

The ‘XData’ are currently indices, and in MATLAB, indexing begins at 1, not 0. To have the time axis vector begin at 0, subtract 1 from ‘tidx’ or equivalently:

Lines.XData = (Lines.XData-1)/Fs;

The last value is then 54.330.

.

[Adam Danz]

Here's an extension to @Star Strider's solution that converts the xdata to seconds and changes the X-ruler to a DurationRuler where the tick labels will include the duration units (sec, in this case).

F = openfig('figure1.fig');
Lines = findobj(F, 'Type','line');
tidx = Lines.XData;
speed = Lines.YData;
Fs = 3E+3;                    % Sampling Frequency (Hz)
tsec = tidx/Fs/24/60/60;      % 
Lines.XData = tsec; 
ax = ancestor(Lines,'axes'); 
set(ax,'XRuler',matlab.graphics.axis.decorator.DurationRuler)