MATLAB: How do i calculate True data values being plotted from a mouse coordinate

MATLAB and Simulink Student Suitematlab coordinatesmouse eventsxdata and ydata from mouse coordinate

I have been trying for hours to do this and i cant figure it out. Here is my problem i am plotting 4 subplots in one figure. The plots come out like i need them and here is an example of one of them

The X is DateTime series that is read in from a csv file, the Y is various statistics that pertain to that DateTime. What i am attempting at doing is to hover my cursor at some point on the subplot and retrieve the values that are not the global coordinates but the real values as they are considered in the plot.

As an example of wanted behavior when i hover over near 1,0 on the subplot above i should get the datetime of Jan 07,20,00(or something close) and the Y value of -1080(or something close)

Here is what i have done so far my main figure is called 'fig' then after everything is plotted i set the callback function

set(fig,'WindowButtonMotionFcn',@mouseMove);

 function mouseMove(object,eventdata)
        c = get(0,'PointerLocation');
        datax1 = get(pl1,'XData');
        datay1 = get(pl1,'YData');
        pos = getpixelposition(p1);
        dim1 = [1420 917 300 20];
        legendString = ['(X,Y) = (', num2str(c(1,1)),', ',num2str(c(1,2)), ')'];
        h1 = uicontrol('style','text','posit',dim1,'backg',mainBackColor,...
            'fontsize',12,'fontweight','bold','string',legendString,...
            'ForegroundColor', nearWhite);
        drawnow;
    end

At the moment it just creates a text field with the global x and y values of the mouse. pl1 is the plot call for one of the subplots. datax1 and datay1 do have the values for that specific plot i just dont know how to turn c(1) and c(2) into a value from datax1 and datay1 that is visually closest to those mouse coordinates.

If anything is missing for you MatLab wizards please ask i can provide more code. Any help or guidance to how to do this is appreciated.

Best Answer

ayar - since you have four subplots (or axes) you will need to determine which axes your mouse cursor is hovering over before you try to determine the (x,y) coordinate for that axes. For example, suppose we plot four sine and cosine curves as

    axesHandles = [];
    hFig = figure;
    xx = -2*pi:0.001:2*pi;
    axesHandles = subplot(2,2,1);
    plot(xx,sin(xx));
    axesHandles = [axesHandles subplot(2,2,2)];
    plot(xx,cos(xx));
    axesHandles = [axesHandles subplot(2,2,3)];
    plot(xx,5*sin(xx));
    axesHandles = [axesHandles subplot(2,2,4)];
    plot(xx,5*cos(xx));

With the above, we create the four subplots and store the handle to each axes. We then assign the WindowButtonMotionFcn as

    set(hFig,'WindowButtonMotionFcn',@mouseMove);
    hText = [];

where hText will be the handle to our text graphics object. (We hold on to this handle because we don't want to create a new text graphics object whenever we move the mouse.) Now are callback will look like

    function mouseMove(hObject,eventdata)
        % get the position of the mouse
        figCurrentPoint = get(hObject, 'CurrentPoint');
        position      = get(hObject, 'Position');
        xCursor       = figCurrentPoint(1,1)/position(1,3); % normalize

        yCursor       = figCurrentPoint(1,2)/position(1,4); % normalize
        % iterate over each axes (subplot) to see where the mouse cursor is
        % hovering over
        isOverAxes = 0;
        for k=1:length(axesHandles)
            hAxes = axesHandles(k);
            % get the position of the axes within the GUI
            axesPos = get(hAxes,'Position');
            minx    = axesPos(1);
            miny    = axesPos(2);
            maxx    = minx + axesPos(3);
            maxy    = miny + axesPos(4);
            % is the mouse down event within the axes?

            if xCursor >= minx && xCursor <= maxx && yCursor >= miny && yCursor <= maxy
                currentPoint = get(hAxes,'CurrentPoint');
                x            = currentPoint(2,1);
                y            = currentPoint(2,2);
                textString = sprintf('(X,Y) = (%.6f,%.6f)', x, y);
                if isempty(hText)
                    hText =  uicontrol('Style', 'text','BackgroundColor', 'r',...
                    'FontSize',10,'FontWeight', 'bold','ForegroundColor', 'k');
                end
                set(hText,'Visible','on','Position', [figCurrentPoint(1,1) figCurrentPoint(1,2) 150 20], 'String', textString);
                isOverAxes = true;
                break;
            end
            if ~isOverAxes &&  ~isempty(hText)
                set(hText,'Visible','off');
            end
        end
    end

In the above, we get the current position of the mouse cursor and normalize it so that we can compare it to the normalized positions of the four axes. We loop over each axes until we find the one which satisfies

    % is the mouse down event within the axes?
    if xCursor >= minx && xCursor <= maxx && yCursor >= miny && yCursor <= may

We then get the current point within the axes which will be your "true" plotted data values. The text floats to the current position of the mouse cursor (rather than being static). See the attached for the full example.

Related Solutions

MATLAB: Dynamically reading cursor location

You can use the WindowButtonMotionFcn callback of the figure object. Run the following example

fig = figure();
ax = axes(fig);
fig.WindowButtonMotionFcn = {@mouseMotionCB, ax};
function mouseMotionCB(fig, event, ax_handle)
    fprintf('Current Point is %f %f %f\n', ax_handle.CurrentPoint(1,1:3));
end

MATLAB: How to move a plotted line vertically with mouse in a GUI

Ruben - here is a quick and rough way to do what I think that you want. It makes several assumptions which are hopefully valid for what you are trying to do, namely that plot (or some equivalent) function is used to plot the data on the 2D axes - so we have access to the x and y data that makes up the graphic. I've used GUIDE to mock up a GUI - it has a single axes (named axes1) and a push button (named pushbutton1). The button is used to plot some data on the axes. Its callback is

 % --- Executes on button press in pushbutton1.
 function pushbutton1_Callback(hObject, eventdata, handles)
 % define an array of colours
 colours = {'b','r','g','k','m','y'};
 % is the plot handles field defined for the handles structure?
 if ~isfield(handles,'plotHandles');
    handles.plotHandles = [];
 end
 % determine the number of handles (a maximum of six are plotted)
 numHandles = mod(length(handles.plotHandles),6);
 % get the x and y data for the sine wave, offset by the number of handles
 x   = -2*pi:0.01:2*pi;
 y   = sin(x) + numHandles;
 % plot the data
 h   = plot(handles.axes1,x,y,colours{numHandles+1});
 % update the plot handles to the array of plot handles
 handles.plotHandles = [handles.plotHandles ; h];
 % save the data


 guidata(hObject,handles);

The above just plots up to six sine waves on the axes. The important part is the saving of the plot graphics handle to the handles structure. This will allow us to manipulate the data later on.

Now, in order to enable the user to move a graphic object on the axes, we are going to assign three callbacks to the GUI/figure. In the Opening function (myGuiName_OpeningFcn), add the following code

 set(hObject, ...
    'WindowButtonDownFcn',   @mouseDownCallback, ...
    'WindowButtonUpFcn',     @mouseUpCallback,   ...
    'WindowButtonMotionFcn', @mouseMotionCallback);

hObject is our GUI/figure, and we are going to create callbacks for the (mouse) button down, up and motion events.

Each callback (within our m-file) is then defined.

The purpose of the mouseDownCallback is to check to see if the mouse down event is within axes1 (as opposed to anywhere else within the GUI). If this is true, then given the position within axes1, find (using the Euclidean distance equation) which plot graphics is closest to this position. This information is then saved for the mouse motion callback.

 function mouseDownCallback(figHandle,varargin)
    % get the handles structure


    handles = guidata(figHandle);
    % get the position where the mouse button was pressed (not released)
    % within the GUI
    currentPoint = get(figHandle, 'CurrentPoint');
    x            = currentPoint(1,1);
    y            = currentPoint(1,2);
    % get the position of the axes within the GUI
    axesPos = get(handles.axes1,'Position');
    minx    = axesPos(1);
    miny    = axesPos(2);
    maxx    = minx + axesPos(3);
    maxy    = miny + axesPos(4);
    % is the mouse down event within the axes?
    if x>=minx && x<=maxx && y>=miny && y<=maxy 
        % do we have graphics objects?
        if isfield(handles,'plotHandles')
            % get the position of the mouse down event within the axes
            currentPoint = get(handles.axes1, 'CurrentPoint');
            x            = currentPoint(2,1);
            y            = currentPoint(2,2);
            % we are going to use the x and y data for each graphic object
            % and determine which one is closest to the mouse down event
            minDist      = Inf;
            minHndl      = 0;
           for k=1:length(handles.plotHandles)
               xData = get(handles.plotHandles(k),'XData');
               yData = get(handles.plotHandles(k),'YData');
               dist  = min((xData-x).^2+(yData-y).^2); 
               if dist<minDist
                   minHndl = handles.plotHandles(k);
                   minDist = dist;
               end
           end
           % if we have a graphics handle that is close to the mouse down
           % event/position, then save the data
           if minHndl~=0
               handles.mouseIsDown     = true;
               handles.movingPlotHndle = minHndl;
               handles.prevPoint       = [x y];
               guidata(figHandle,handles);
           end
        end
    end

The purpose of the mouseUpCallback is to just reset any fields that correspond to the moving of the graphic, indicating that we are finished with the move.

 function mouseUpCallback(figHandle,varargin)
    % get the handles structure
    handles = guidata(figHandle);
    if isfield(handles,'mouseIsDown')
        if handles.mouseIsDown
            % reset all moving graphic fields
            handles.mouseIsDown     = false;
            handles.movingPlotHndle = [];
            handles.prevPoint       = [];
            % save the data
            guidata(figHandle,handles);
        end
    end

Finally, the purpose of mouseMotionCallback is to move the graphic from the previous position to the current one.

 function mouseMotionCallback(figHandle,varargin)
    % get the handles structure
    handles = guidata(figHandle);
    if isfield(handles,'mouseIsDown')
        if handles.mouseIsDown
            currentPoint = get(handles.axes1, 'CurrentPoint');
            x            = currentPoint(2,1);
            y            = currentPoint(2,2);
            % compute the displacement from previous position to current
            xDiff = x - handles.prevPoint(1);
            yDiff = y - handles.prevPoint(2);
            % adjust this for the data corresponding to movingPlotHndle
            xData = get(handles.movingPlotHndle,'XData');
            yData = get(handles.movingPlotHndle,'YData');
            set(handles.movingPlotHndle,'YData',yData+yDiff,'XData',xData+xDiff);
            handles.prevPoint = [x y];
            % save the data
            guidata(figHandle,handles);
        end
    end

I've attached the code to this answer. Hope that it helps!

Best Answer

Related Solutions

MATLAB: Dynamically reading cursor location

MATLAB: How to move a plotted line vertically with mouse in a GUI

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