How can I plot a circle use given point?

I want to plot a circle, use given data.

but, I just know the some of the point in circle, but do not midpoint and radius.

Then, How Can I plot the circle using a given point?

Answer 1

[KSSV]

If you have points.....you can find the radius of circle. It depends on how many points you know.

Frame the distance formula and solve the equations.

If you have lot of points use: https://in.mathworks.com/matlabcentral/fileexchange/22643-circle-fit-pratt-method

Answer 2

[weikang zhao]

If you have coordinates of three points, the radius and center of the circle can be obtained by solving a positive definite equation set. If you have more points, there will be a overdetermined set, the midpoint and radius have a least squares estimation.

[Seong-Won Ham]

Thanks for your ccomments.

Now, I have a lot of point data and will try least squares estimation to find the equation.

I wonder that the best code of calculate radius.

If you have an idea of code, Please comment for me.

I'm sorry that my poor english.

thanks.

[weikang zhao]

give you a demo:

clear
c=[5;5];%real coordinate of midpoint
r=3;%real radius
pointNum=20;%num of all the points
thetatrain=unifrnd(0,2*pi,1,pointNum);
rtrain=r+0.01*randn(1,pointNum);
xytrain=c+[rtrain.*cos(thetatrain);rtrain.*sin(thetatrain)];%Generate a set of points perturbed around the circle
plot(xytrain(1,:),xytrain(2,:),'.');
A=[xytrain.',ones(pointNum,1)];
b=sum(xytrain.^2).';
est=(A.'*A)\A.'*b;
rhat=sqrt(est(1)^2/4+est(2)^2/4+est(3));%LS estimate of radius
xhat=est(1)/2;%LS estimate of the x coordinate of midpoint
yhat=est(2)/2;%LS estimate of the y coordinate of midpoint
hold on;
plot(xhat+rhat*cos(0:pi/180:2*pi),yhat+rhat*sin(0:pi/180:2*pi));

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