How to plot a circle on top of my plotted image

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Ruben Alfaro
Ruben Alfaro 2014-5-9
回答： Hugo Diaz 2022-2-5
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

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回答（4 个）

lvn
lvn 2014-5-9
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
Ruben Alfaro
Ruben Alfaro 2014-5-9
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?
Image Analyst
Image Analyst 2014-5-9
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;
Hugo Diaz
Hugo Diaz 2022-2-5
%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

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