To plot an ellipse

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Priya 2014-5-12

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评论： Waqar Khan 2021-3-18

Hi,

I have got the semi axes, with that how to plot an ellipse in matlab. I have tried using the function 'pdeellip', but it didn't work out. Please do help.

Thanks in advance.

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Image Analyst 2014-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/129273-to-plot-an-ellipse#answer_136506

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_an_ellipse.3F

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Waqar Khan 2021-3-18

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Hi there, I need help with creating ellipse, I have X = 0.666 and Y=0.87 values, I need to make ellipse from X and Y, kindly guide me. Looking forward to hearing from you.

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Walter Roberson 2021-3-18

编辑：Walter Roberson 2021-3-18

在 MATLAB Online 中打开

xCenter = 0;

yCenter = 0;

xRadius = 2/3;

yRadius = 0.87;

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

%theta(end) = [];

x = xRadius * cos(theta) + xCenter;

y = yRadius * sin(theta) + yCenter;

xvec = linspace(min(x), max(x), 50);

yvec = linspace(min(y), max(y), 50) .';

h = fill(x, y, [0 0 .5], 'FaceAlpha', 0.3); axis equal; xlabel('x'); ylabel('y')

figure

P = 3;

G = 10*exp(-((xvec-xCenter).^2+(yvec-yCenter).^2)./P);

surf(xvec, yvec, G, 'edgecolor', 'none'); view(3); xlabel('x'); ylabel('y'); zlabel('G');

figure

d = sqrt(((xvec-xCenter)./xRadius).^2 + ((yvec-yCenter)./yRadius).^2);

d1 = d <= 1;

surf(xvec, yvec, double(d1), 'edgecolor', 'none'); axis equal; xlabel('x'); ylabel('y'); zlabel('Inside');

figure

G1 = G;

G1(~d1) = nan;

surf(xvec, yvec, G1, 'edgecolor', 'none'); xlabel('x'); ylabel('y'); zlabel('G');

Which is to say that the G matrix here is a gaussian based upon distance from a center, and that G1 is G masked so that everything outside the ellipse is nan. Possibly for your purpose it might make more sense to assign 0 to such places.

Walter Roberson 2021-3-18

Note: The P in the equation for G controls how quickly the Gaussian drops off. You should decide more carefully how much you want the gaussian to fall off by the edge of the ellipse.

Also note that what this implements is a circular guassian "clipped" by an ellipse. You could instead make the gaussian itself elliptical, by modifying distance from the center according to the ellipse parameter.

IIt is possible that what you need to do is construct an elliptical gaussian filter, such as for blurring purposes. You would proceed a bit differently in a case like that.

Waqar Khan 2021-3-18