How to create a moving filled-color circle in non-square limits for x and y axes?

I'm using viscircle to create a moving circle in a non-square limits for x and y axes, but this makes the moving circle become ellipse. Can someone help me to get a circle and that is aslo filled-color?

I also have another question. Is there a way to save the same amount of images as .gif but with a smaller size?

close all
load('z_p.mat')
dt = 1e-4;

h = figure;
filename = 'zp.gif';
for m = 1:100:length(z_p)
    cla % clear the axes
    
    % fix the axis limits
    xlim([0 length(z_p)*dt]);
    ylim([1.2*min(z_p(:,1)) 1.2*max(z_p(:,1))]);
    
    centers = [m*dt z_p(m,1)]; % circule center
    radius = 0.2; % circule radius
    
    viscircles(centers,radius,'Color','b','LineWidth',2);
    hold on; p1 = plot((1:m)*dt,z_p(1:m,1));
    grid on
    drawnow
    
    % capture the plot as an image
    frame = getframe(h);
    im = frame2im(frame);
    [imind,cm] = rgb2ind(im,256);
    
    % write to the GIF File
    if m == 1
        imwrite(imind,cm,filename,'gif','Loopcount',inf);
    else
        imwrite(imind,cm,filename,'gif','WriteMode','append');
    end
end

[Baran Uslu]

Dear Ahmad,

Can the problem be with the axes settings, because when a circle becomes an ellipse we must think about an aspect problem. Hope you already fixed it.

Answer 1

[Suraj Kumar]

Hi AHMAD,

To achieve a moving circle filed with colour in non-square limits for x and y axes you can go through the following steps along with the code snippets:

1. You can use the command “axis equal” after setting the axes limits to ensure the aspect ratio is maintained.

xlim([0 length(z_p)*dt]); 
ylim([1.2*min(z_p(:,1)) 1.2*max(z_p(:,1))]); 
axis equal; 

2. The “viscircles” function does not natively support filling of the circle. To create a filled circle, you can use the “rectangle” function with the “Curvature” property set to [1,1], which transforms the rectangle into a circle.

3. The “FaceColor” and “EdgeColor” properties can also be used to fill the interior part and set the outline, effectively creating a filled circle.

rectangle('Position',[centers(1)-radius, centers(2)-radius, 2*radius, 2*radius],... 
              'Curvature',[1,1], 'FaceColor','b', 'EdgeColor','b'); 
    hold on; 
    p1 = plot((1:m)*dt,z_p(1:m,1)); 
    grid on 
    drawnow 

You can refer the following image for better understanding:

For more insights on the axis in MATLAB and “rectangle” function you can go through the following documentations:

1. https://www.mathworks.com/help/matlab/ref/axis.html
2. https://www.mathworks.com/help/matlab/ref/rectangle.html