How to plot a circle on top of my plotted image

I have an image plotted and I wanted to plot a circle on top of it with the same centroid of the image.

I want the radius to be 500 and I want it done with a red color, of somebody could help me with this.

thank you very much

Answer 1

[lvn]

See this answer http://www.mathworks.com/matlabcentral/answers/98665-how-do-i-plot-a-circle-with-a-given-radius-and-center

To plot on top of an existing figure, start with

hold on

Answer 2

[Ruben Alfaro]

Thank you,

But it doesnt seem to work for me, maybe im doing something wrong. can somebody help me figure it out or recommend another way of doing this?

[Roberto]

post the error you're having, or explain why it doesn't work for you?

Answer 3

[Image Analyst]

Try this:

grayImage = imread('concordorthophoto.png');
imshow(grayImage);
axis on;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
[rows, columns, numberOfColorChannels] = size(grayImage);
hold on; % Don't let plot blow away the image.
xCenter = columns / 2;
yCenter = rows / 2;
theta = 0 : 0.01 : 2*pi;
radius = 500;
x = radius * cos(theta) + xCenter;
y = radius * sin(theta) + yCenter;
plot(x, y, 'r-', 'LineWidth', 3);
grid on;

Answer 4

[Hugo Diaz]

%The trick is to do it 3D, and a 2D plot is like a view from above.

% your 2D plot. If your function f(x,y) < m, then

hold on

r = 1;

teta = -pi:0.01:pi;

x = r * cos(teta);

y = r * sin(teta);

plot3(x, y, m * ones(1, numel(x)), 'Color','k')

hold off