How to plot circle with direction?

I wish to plot a circle with direction of its motion.An exmaple is attached below.

I wish to get around 5-10 arrows per circle (that can be chnaged as per our need).

Below attached matlab.mat file is the data file.

The code goes like:

subplot(2,2,[1 3])
h1 = plot(x, y, '-','Color','b','LineWidth',2);

Now I dont know how to put 5-10 arrows showing direction.

Can anyone help?

Answer 1

[Bruno Luong]

2D version. adapt to your need

% circle parameter
r = 5;
cx = 0;
cy = 0;

cfun = @(tt) [cx+r*cos(tt); cy+r*sin(tt)];
xy = cfun(linspace(0,2*pi,361));

close all
hold on

plot(xy(1,:),xy(2,:),'b');
% arrows parameters
m = 10; % number of arrows
h = 0.1*r; % height
w = 0.1*r; % width
dir = -1; % 1 anticlock, -1 clock
a = [-w/2 0 w/2;
      -dir*h  0 -dir*h];
for k=1:m
    tt = 2*pi*k/m;
    R = [cos(tt) -sin(tt);
         sin(tt)  cos(tt)];
    xy = cfun(tt)+  R*a;
    plot(xy(1,:),xy(2,:),'b');
end
axis equal

[Bruno Luong]

3D version:

% circle parameters
r = 5;
cxyz = [0; 0; 0]; % center
N = randn(3,1); % normal to circle plane

N = N(:)/norm(N);
Q = null(N');
cfun = @(tt) cxyz + r*Q*[cos(tt); sin(tt)];

close all
hold on

xyz = cfun(linspace(0,2*pi,361));
plot3(xyz(1,:),xyz(2,:),xyz(3,:),'b');
% 3D arrows parameters
m = 10; % number of arrows
h = 0.12*r; % height
w = 0.08*r; % width
dir = -1; % 1 anticlock, -1 clock
p = 16; % #circular discretization of the arrow
phi = linspace(0,2*pi,p+1);
Va = [(w/2)*cos(phi);
      (-dir*h)+zeros(size(phi));
      (w/2)*sin(phi)];
Va(:,end+1) = [0; 0; 0];
F = [ 1:p;
      2:p+1;
     (p+2)+zeros(1,p)].';
F2 = 1:p+1; 
Q = [Q, N];
for k=1:m
    tt = 2*pi*k/m;
    R = [cos(tt) -sin(tt)  0;
         sin(tt)  cos(tt)  0;
         0        0        1];
   Vk = cfun(tt)+  Q*R*Va;
   patch('Faces', F, 'Vertices', Vk', 'FaceColor', 'b', 'EdgeColor', 'none');
   patch('Faces', F2, 'Vertices', Vk', 'FaceColor', 'b', 'EdgeColor', 'none');
end
axis equal
view(3);

[Megha]

@Bruno Luong: you have definately put a lot of efforts and that I really appriciate.

Surely, this would be useful to me for my future reference.

Could you please help me out with the data that I have attached with this?

Or how to put arrows to the figure like goven below:

[Bruno Luong]

No sorry, I won't process your data.

I let you adapt the code and plot exactly the way you like. If you have specific question feel free to ask.

[Megha]

I have tried the following code, but arrows are too close to each other, in this case, to see the dirction of motion of circle.

rMag = 0.5;
lenTime = length(x);

% Indices of tails of arrows
vSelect0 = 1:(lenTime-1);
% Indices of tails of arrows
vSelect1 = vSelect0 + 1;

% X coordinates of tails of arrows
vXQ0 = x(vSelect0, 1);         % x last removed
% Y coordinates of tails of arrows
vYQ0 = y(vSelect0, 1);           % y last removed

% X coordinates of heads of arrows
vXQ1 = x(vSelect1, 1);           % x first removed
% Y coordinates of heads of arrows
vYQ1 = y(vSelect1, 1);            % y first remove

% vector difference between heads & tails
vPx = (vXQ1 - vXQ0) * rMag;
vPy = (vYQ1 - vYQ0) * rMag;

% add arrows 
h2 = quiver (vXQ0,vYQ0, vPx, vPy, 0, 'b'); grid on; hold off
axis equal

[michael]

I'w suggest to set

X = 10; % this is step size - each 10th point will have a vector
vSelect0 = 1:X:(lenTime-1);