zoom on the mouse pointer

Hi, I made an app on the app Designer and I created a function for zooming on a plot using the location of the mouse pointer. Here is how it works and the script of the function:

function UIFigureWindowButtonMotion(app, event)
    pointerLocation = get(app.UIFigure,'CurrentPoint'); %location of pointer
        axisYcoords = [app.UIAxes.InnerPosition(2),...
            app.UIAxes.InnerPosition(2) + app.UIAxes.InnerPosition(4)]; %UIAxes y coordinates
        axisXcoords = [app.UIAxes.InnerPosition(1),...
            app.UIAxes.InnerPosition(1) + app.UIAxes.InnerPosition(3)]; %UIAxes x coordinates
        
        %if you're pointing inside the UIAxes and if there is data in the UIAxes. 
        if pointerLocation(1) > axisXcoords(1) &&...
                pointerLocation(1) < axisXcoords(2) &&...
                pointerLocation(2) > axisYcoords(1) &&...
                pointerLocation(2) < axisYcoords(2) &&...
                ~isempty(app.UIAxes.Children)
                        
            ZoomMag = 10; %zoom magnification
            xCalibrate = (app.UIAxes.XLim(2) - app.UIAxes.XLim(1))/...
                app.UIAxes.InnerPosition(3); %x value per UIAxes inner pixel
            yCalibrate = (app.UIAxes.YLim(2) - app.UIAxes.YLim(1))/...
                app.UIAxes.InnerPosition(4); %y value per UIAxes inner pixel
            
            %find what your x and y value are at your cursor within the UIAxes
            xValue = xCalibrate*(pointerLocation(1)-app.UIAxes.InnerPosition(1));
            yValue = yCalibrate*(pointerLocation(2)-app.UIAxes.InnerPosition(2));
            
            [A, map] = imread(app.fullfilename);
            A = flipud(A);
            %plot the pointer location as a blue dot and plot the original data on UIAxes2
            hold(app.UIAxes,'on');
                           
            h = findobj(app.UIAxes2,'Type','line');
            delete(h);
            
            image([A, map], 'parent', app.UIAxes2);
            set(app.UIAxes2,'YDir','normal')
            
            plot(app.UIAxes2, xValue, yValue, 'b.', 'MarkerSize', 15);
            pause(0.0000000000000000001);
            
            %adjust the x and y limits on UIAxes2
            xlim(app.UIAxes2,...
                [xValue - (app.UIAxes.XLim(2) - app.UIAxes.XLim(1))/ZoomMag,...
                xValue + (app.UIAxes.XLim(2) - app.UIAxes.XLim(1))/ZoomMag])
            ylim(app.UIAxes2,...
                [yValue - (app.UIAxes.YLim(2) - app.UIAxes.YLim(1))/ZoomMag,...
                yValue + (app.UIAxes.YLim(2) - app.UIAxes.YLim(1))/ZoomMag])
        end
end

in this case it all worked fine, but then I insert the line "axis(app.UIAxes, 'equal');" to maintain the original ratio of the image and the X value in the zoomed area is now shifted to the right. In the second image I was pointing at 100 on the X axis and it shows me the right end of the plot. I need to recalibrate the xValue, but I don't know where to insert some changes.

[Jiri Hajek]

Hi, note that you are using the InnerPosition property of the axes, but this is insufficient in your second case. Look here for a proper way to achieve your goal: https://www.mathworks.com/help/matlab/creating_plots/automatic-axes-resize.html

[Luca Tognetti]

thanks for the quick reply, but this didn't help me that much... what you suggest to implement?

[Mario Malic]

Maybe this can help: https://www.mathworks.com/help/matlab/creating_plots/aspect-ratio-for-2-d-axes.html

Answer 1

[Kartik]

Hi,

To recalibrate the 'xValue' after setting the aspect ratio of the axes to 'equal', you need to modify the 'xCalibrate' variable to include the aspect ratio adjustment. You can calculate the aspect ratio of the axes by dividing the width by the height of the 'UIAxes' 'InnerPosition' property, and then adjust 'xCalibrate' accordingly. Here's how you can modify the 'xCalibrate' calculation:

% calculate the aspect ratio of the axes
aspectRatio = app.UIAxes.InnerPosition(3)/app.UIAxes.InnerPosition(4);

% adjust xCalibrate to account for the aspect ratio
xCalibrate = (app.UIAxes.XLim(2) - app.UIAxes.XLim(1))/(app.UIAxes.InnerPosition(3)*aspectRatio);

Replace the existing 'xCalibrate' calculation in your code with the above lines, and it should recalculate 'xValue' correctly after setting the aspect ratio.