Keep tracking the center of a ball with positional updates - matlab

Question

In the code below, I am attempting to move a ball from 90 degrees to 44 degrees and back to 90 degrees. I wanted to be able to track the position of the ball's center point. I am trying to do this by plotting a marker that follows the ball. I would also like to keep seeing the (x,y) position of the ball being updated as the ball moves.
Can you help me modify my code so that:
1. The marker remains in the center of the ball, and
2. Keep displaying the (x,y) position of the marker (ball's center) as it moves?
Here is what I have done so far:
close all; clc; clear;
% Define position of arm
theta=0:10:360; %theta is spaced around a circle (0 to 360).
r=0.04; %The radius of our circle.
%Define a circular magenta patch.
x=r*cosd(theta) + 0.075;
y=r*sind(theta) + 1;
% Size figure and draw arms
figure('position', [800, 300, 600, 550]);
point = plot(0.075,1, 'bo', 'markers', 3);
hold on
myShape2=patch(x,y,'m');
set(myShape2,'Xdata',x,'Ydata',y);
axis([-1.5 3 -1 3]); grid on;
n = 1;
T=0.15; %Delay between images
for theta = pi/2:-pi/90:0,
if theta >= pi/4;
theta = theta;
else
theta = pi/2 - theta;
end
Arot = [sin(theta) cos(theta); -cos(theta) sin(theta)];
xyRot = Arot * [x; y]; % rotates the points by theta
xyTrans = xyRot;
point = plot(xyTrans(1, n),xyTrans(2, n), 'bo', 'markers', 3);
hold on;
set(myShape2,'Xdata',(xyTrans(1, :)),'Ydata',(xyTrans(2, :)));
pause(T); %Wait T seconds
end
Thanks for your time and help!

Answer 1

close all; clc; clear;
% Define position of arm
theta=0:10:360; %theta is spaced around a circle (0 to 360).
r=0.04; %The radius of our circle.
%Define a circular magenta patch.
x=r*cosd(theta) + 0.075;
y=r*sind(theta) + 1;
% Size figure and draw arms
figure('position', [800, 300, 600, 550]);
hold on
myShape2=patch(x,y,'m');
set(myShape2,'Xdata',x,'Ydata',y);
point = plot(0.075,1, 'bo', 'markers', 1);
dim = [.2 .5 .3 .3];
axis([-1.5 3 -1 3]); grid on;
T=0.15;
% Create annotation object to display object center
ano = annotation('textbox',dim,'String',['center position: (','0.075, 1'],'FitBoxToText','on');
for theta = pi/2:-pi/90:0,
if theta >= pi/4;
theta = theta;
else
theta = pi/2 - theta;
end
Arot = [sin(theta) cos(theta); -cos(theta) sin(theta)];
xyTrans = Arot * [x; y];
% Remove plot and annotation object from previous frame
delete(point)
delete(ano)
set(myShape2,'Xdata',(xyTrans(1, :)),'Ydata',(xyTrans(2, :)));
% Calculate the center of the patch as mean x and y position
x_pos = mean(xyTrans(1, :));
y_pos = mean(xyTrans(2, :));
point = plot(x_pos, y_pos, 'bo', 'markers', 1);
ano = annotation('textbox',dim,'String',['center position: (',sprintf('%0.3f', x_pos),', ',...
sprintf('%0.3f', y_pos),')'],'FitBoxToText','on');
axis([-1.5 3 -1 3]); grid on;
pause(T);
end