How to make circle in matrix form

Hi guys,

is it possible to draw a circle in matrix form on matlab?

thanks!

Answer 1

[Star Strider]

I am not certain what th desired result is.

This is the best I can do —

k = 10;
M = zeros(k);
v = 0:0.2:k-2;
x = ceil(k/2+k/2*cos(2*pi*v/max(v)));
x(x==0) = 1;
y = ceil(k/2+k/2*sin(2*pi*v/max(v)));
y(y==0) = 1;
ix = sub2ind(size(M), x, y);
M(ix) = 1

M = 10×10

0 0 1 1 1 1 1 1 0 0 0 1 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 1 0 0 0 1 1 1 1 1 1 0 0

figure
spy(M)
grid

.

Answer 2

[Simon Chan]

Another option using function pol2cart:

clear; clc;
separation = 1;                             % Angle separation, 1 degree
rho = 15;                                   % Radius, 15 pixels
num_dot = 360/separation +1;                % Total number of points
theta = linspace(-pi,pi,num_dot);           % Theta separation
cx = 50;                                    % Your center point, x-coordinates = 50 (example)
cy = 25;                                    % Your center point, y-coordinates = 25 (example)
[xA,yA] = pol2cart(theta,rho);              % Use pol2cart
A = zeros(100,100);                         % Original region, example, size: 100x100
[Ny, Nx]= size(A);
xA_convert = round(cx-xA);                  % Convert back from polar coordinates
yA_convert = round(cy-yA);
for k = 1:num_dot
    A(yA_convert(k),xA_convert(k)) =1;      % Put the dots in matrix A
end
figure(1)
plot(cx,cy,'ro');                           % Your center point
hold on
plot(xA_convert,yA_convert,'b+')
xlim([0 Nx])
ylim([0 Ny])
figure(2)
imshow(A)

Results:

Showing Matrix A using function imshow:

Answer 3

[Image Analyst]

See the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_do_I_create_a_circle.3F