Moving a circle around a point along with it.

Suppose i have a point located at (5,5) having a circle of radius 1 around it. If the point moves from 5,5 to any other point say (0,0). The circle should also move with it.

Can someone give the matlab code for this.

Answer 1

[Sugandhi]

Hi Pallov Anand,

I understand that If the point moves from 5,5 to any other point say (0,0). The circle should be drawn with center as (0,0).The code you requested could be like this:

% Define initial position of point and radius of circle
x = 5;
y = 5;
r = 1;

% Create figure window and draw initial point and circle
figure;
hold on;
plot(x, y, 'ro');
viscircles([x, y], r);

% Define new position of point
new_x = 0;
new_y = 0;

% Move point and circle to new position
dx = new_x - x;
dy = new_y - y;
x = new_x;
y = new_y;
clf;
hold on;
plot(x, y, 'ro');
viscircles([x, y], r);

% Repeat the above code to move the point and circle to any other position as desired

In this code, x and y represent the x and y coordinates of the point, and r represents the radius of the circle. The `viscircles` function is used to draw the circle around the point.

To move the point and circle to a new position, we first define the new position by setting new_x and new_y to the desired coordinates. We then calculate the difference between the new position and the current position using dx = new_x - x and dy = new_y - y. Finally, we update x and y to the new position, and redraw the point and circle at the new location.

You can repeat the code to move the point and circle to any other position as desired.

[VBBV]

The code can be done more precise using below code

% Define initial position of point and radius of circle
x = 5;
y = 5;
r = 1;

% Create figure window and draw initial point and circle
figure;
h1 = plot(x, y, 'ro');
h2 = viscircles([x, y], r);

pause(0.1)  % choose a suitable value as per your need

h1.XData = 0;
h1.YData = 0;
h1.Color = 'w';
delete(h2)

% Define new position of point by interactive input
new_x = randi([-10 10],1) %input('Enter new x coordinate:')

new_x = 3

new_y = randi([-10 10],1) %input('Enter new y coordinate:')

new_y = -1

% Move point and circle to new position
viscircles([new_x, new_y], r,'Color','b');
Lim = abs(max([new_x new_y]));
xlim([-Lim-2 Lim+2]);ylim([-Lim-2 Lim+2]);

[Pallov Anand]

Thanks @Sugandhi and @VBBV for the replies. It was helpful. Moreover, can you guys send me the code showing an animation for the same.

Like a point which is at 5,5 which has been encircled by a circle havinf center at 5,5 and radius 1. As the point moves from (5,5) to (0,0), the circle should around it also should move with it. Is this possible. Point can move straight or in any random way, but straight path would be easy to implement i guess.

[Pallov Anand]

clc

clear all

close all

x_r(1,1) = 5;

y_r(1,1) = 5;

dt = 0.01;

t_span = 10;

t = 0:dt:t_span;

r = 2;

Xc = x_r(1,1);

Yc = y_r(1,1);

for n = 1 : length(t)

xd(1,:) = r*cos(t) + Xc;

yd(1,:) = r*sin(t) + Yc;

x_r(1, n+1) = x_r(1, n) + dt * (0.4);

y_r(1, n+1) = y_r(1, n) + dt * (0.4);

end

figure(1)

axis([2 15 0 20]);

hold on

p = plot( x_r(1,1), y_r(1,1),'o','MarkerFaceColor','red','MarkerSize',3.5);

hold on

plot(xd,yd, 'o','MarkerFaceColor','blue','MarkerSize',1);

hold on

for k=1:length(t)

title(['Time = ',num2str(k*dt)])

hold on

p.XData = x_r(1,k,1);

p.YData = y_r(1,k,1);

desired.XData = xd(1,k,1);

desired.YData = yd(1,k,1);

drawnow

pause(0.001);

end

In the above code, the point is moving but the circle is at the original position only. How can I make the circle move along with the point.

[Pallov Anand]

Got it.

x_r(1,1) = 5;

y_r(1,1) = 5;

dt = 0.01;

t_span = 10;

t = 0:dt:t_span;

r = 2;

Xc = x_r(1,1);

Yc = y_r(1,1);

figure(1)

axis([2 15 0 20]);

hold on

% draw the circle centered at the initial position of the point

th = linspace(0, 2*pi, 100);

xc = r*cos(th) + Xc;

yc = r*sin(th) + Yc;

circle = plot(xc, yc, 'b-');

% plot the initial position of the point

p = plot( x_r(1,1), y_r(1,1),'ro','MarkerFaceColor','red','MarkerSize',3.5);

for n = 1 : length(t)

x_r(1, n+1) = x_r(1, n) + dt * (0.4);

y_r(1, n+1) = y_r(1, n) + dt * (0.4);

% update the position of the point

p.XData = x_r(1,n+1);

p.YData = y_r(1,n+1);

% update the position of the circle to match the new position of the point

Xc = x_r(1,n+1);

Yc = y_r(1,n+1);

xc = r*cos(th) + Xc;

yc = r*sin(th) + Yc;

circle.XData = xc;

circle.YData = yc;

title(['Time = ',num2str(n*dt)])

drawnow

pause(0.01);

end

This is what I wanted. Thanks again

[VBBV]

You can use Matlab built in function animatedline to do the same in simpler way as below

clearvars
close all
% Present position of centre of circle
Xc = 2;
Yc = 4;
r = 3;
% define axes 
axis([-10,10,-10,10])
th = linspace(0, 2*pi, 1000);

% new position ( can also get from user input) 
Xnew = 5;
Ynew = 3;
DisX = linspace(Xc,Xnew,30);
DisY = linspace(Yc,Ynew,30);
h = animatedline('Marker','.','Color','b');grid

for k = 1:length(DisX)    
    xc = r*cos(th) + DisX(k);
    yc = r*sin(th) + DisY(k);
    addpoints(h,xc,yc);   
    drawnow    
    pause(0.1)
    clearpoints(h)
end
addpoints(h,xc,yc)

drawnow

[Pallov Anand]

Thanks for this too. This also works.