plot Datetime on x Axes

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MoHa 2020-3-9

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https://ww2.mathworks.cn/matlabcentral/answers/509832-plot-datetime-on-x-axes

评论： Noah Prisament 2023-7-19

Hello! I have a endless while loop, that generates every 20 min a number. I'm trying to figure out how to plot the data with the dates on the x axis and numbers on the Y.

how can i plot the date and time on x axes?

I'm pretty new to Matlab, would really appreciate any help!

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Answer 1

Benjamin Großmann 2020-3-9

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There are mainly 2 possibilities

You can use datetick() to format your x axis ticks to date or time values
You can define your x-values as datetime() and the plot command automatically formats your x-axis with dateticks

For a mwe, we can assume that we start "now" and are collecting data for 12 hours resutling in a time vector t

t = datetime('now'):minutes(20):datetime('now')+hours(12);
y = rand(size(t));
plot(t, y)

You can also append t with the current time

t = []; % initialization
% ...
% ...
% ...
% every iteration / callback
t(end+1) = datetime('now');

As you are new to matlab, i would also recommend not to use a "endless while loop, that generates every 20 min a number". Have a look at the timer class. With the timer class you can define an instance of the timer which calls a function (schedules) every 20 minutes "in the background". Please let me know if you need help with that.

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MoHa 2020-3-9

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Thanks you for your answer Benni,

t = datetime('now'):minutes(20):datetime('now')+hours(12);

this is for only next 12 hours. actually i work on a permanent Monitoring and i get the data eyery for Example 30 min (adjustable in my GUI). in every period my code calculates a number at specific time. i want to plot the numbers with the his time on x axes. therefore i have to have a unlimited time (not limited of 12 hours). i attached my func. please tell how can i optimise my code (ex. timer).

other question is abaout: tic - toc

i dont know why gives me this a wrong diuration. this code takes for ex. 4 minutes time, but tic toc displays some seconds ??

if ~isempty(instrfind)
    fclose(instrfind);
    delete(instrfind);
end
% global S; 
global ComPort; global baudrate;global ScanFullName; %global newFileName;
global newFileNameExtra; global StP;
S=serial(num2str(ComPort),'Baudrate',str2num(baudrate));
fopen(S);
t1=datestr(now);
disp(t1)
    %  code ...
hi=1.453;
% i get the time from my gui
Repeat=str2double(get(handles.MonitoringTime,'String'));
Repeat=Repeat*60;
plt=animatedline('color','r');
hold on
grid on
xlabel('Time [Minutes]','color','w');
ylabel( '3d-Displacement [Meter]','color','w')
title('Station stability');
set(gca,'xcolor','w','ycolor','w')
    while true
        tic
% 1 Cal & Set PPM 
        
         %func ...
% set the ppm 
           %  code ....
% 2 Ref. Points Measurement  
        
          %  func ...
% 3 Prepare the Meseurements and Reference File to Helmert Transformation
        
            %  func ...
% 4 Calc. Station Coord. with Helmert Transformation & Set Coord.
            if ~isempty(instrfind)
                fclose(instrfind);
                delete(instrfind);
            end
            S=serial(num2str(ComPort),'BaudRate',str2num(baudrate));
            fopen(S);
            fst=fopen(newFileNameExtra,'a');
            [xyz,tp,ac,tr]= freeStation_with_HelmertTr;
            St3d_Dist=sqrt(((StP(1)-xyz(1))^2)+((StP(2)-xyz(2))^2)+((StP(3)-xyz(3))^2));
            assignin('base','St3d_Dist',St3d_Dist);
% plotting the data (y) and time (x)             
            t = datevec(now);
            q=t(1,5);
            addpoints(plt,q,St3d_Dist);
            view(handles.StAndRefDisplacement)
            drawnow
       
            % set the calculated coord. with Hel. Transformation
                % code... 
% Writting data into a file
            fprintf(fst,'StationCoordinate:\n');
            fprintf(fst,'\t %d %d %d\n', xyz); 
            fprintf(fst, 'Translation for measured Points resultet from Helmert Transformation\n'); 
            fprintf(fst, '\t %d \t %d \t %d \t \n', tr);
            fprintf(fst,'ThreeD_Difference_to_first_StationCoordinate:\n');
            fprintf(fst, '\t %d \n', St3d_Dist);
            fprintf(fst, 'Transformation Parameter of measured Points resultet from Helmert Transformation\n'); 
            fprintf(fst, '\t %d \n', tp);
            fprintf(fst, 'Accuracy of Helmert Transformation of measured Points\n'); 
            fprintf(fst, '\t %d \n', ac);
            fclose('all');
            movefile(newFileNameExtra, 'output_clouds')
% 5 Start Scanning
        scannerEditedMe_successfullyDone
        fprintf('Scanning Successfully done!\n')    
        t2=datestr(now)
        disp([t1;t2])
        T=toc
        pause(Repeat-T)
        
    end

thanks for your help

Benjamin Großmann 2020-3-9

在 MATLAB Online 中打开

Let's use a simple example as introduction:

clearvars
close all
clc
delete(timerfindall);
t = timer; % timer instance
t.ExecutionMode = 'fixedRate'; % can be 'singleShot', 'fixedRate', 'fixedDelay', 'fixedSpacing'
t.Period = 0.1; % Period in seconds
t.StartFcn = @myTimerInit; % function which is evaluated at start of timer --> initialization
t.TimerFcn = @myTimerFunction; % function which is evaluated every period
t.start % start the timer#+
% use t.stop to stop the timer, timerfindall to find all timers and delete(timerfindall) to delete all timers

The StartFcn

function myTimerInit(src, evnt)
    % some initial values, could also be datetime.empty, but then plotting
    % makes some problems
    src.UserData.t = datetime('now');
    src.UserData.y = 0;
    
    src.UserData.fig = figure('CloseRequestFcn', {@myCloseRequestFcn, src});
    src.UserData.ax = axes('Parent', src.UserData.fig);
    src.UserData.p = plot(src.UserData.ax, src.UserData.t, src.UserData.y);
end

The TimerFcn

function myTimerFunction(src, evnt)
    src.UserData.t(end+1) = datetime('now'); % you can also do some windowing etc. to limit the length of the vector
    src.UserData.y(end+1) = rand;
    
    src.UserData.p.XData = src.UserData.t;
    src.UserData.p.YData = src.UserData.y;
end

The close request of the figure to stop the timer before closing the figure

function myCloseRequestFcn(src, evnt, mytimer)
if isvalid(mytimer)
    mytimer.stop;
    mytimer.delete;
end
closereq

Benjamin Großmann 2020-3-9

You can set the timer interval via the period property of the timer class. See line 9 in my first code snippet.

First, write a function and put everything inside the function which should be evaluated with the specified rate. This is going to be your timerFcn. Please note that a timer fcn (and other callbacks) must have an input argument for the source and event. You can add additional arguments and pass values to those callbacks like i did with the myCloseRequestFcn().

If you want to store data, you can use the UserData of the timer class as I did with the x data, y data and so on.

Then you just have to adapt the definition of the timer instance from my first code snippet.

If you can post a mwe of your problem, than I can try my best to support you with the timer function.

Noah Prisament 2023-7-19

在 MATLAB Online 中打开

The "animatedline" now supports datetimes and durations for all axes as of R2023a!

So, you no longer need to convert your datetimes into a "datevec" which should give your plots a nicer looks with better axes ticks. In order to plot your data on an "animatedline" you can now utilize the following example:

h = animatedline(NaT, NaN);
addpoints(h, Xdata, Ydata);

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plot Datetime on x Axes

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