![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/971710/image.jpeg)
Fit a least squares ellipse
17 次查看(过去 30 天)
显示 更早的评论
I am trying to fit a least square ellipse to to the 'ellipse' data set that i have attached
I feel like i have everything correct (i might not have) but i am struggling plottting the ellipse function 'f'. i keep getting the following error
Warning: Error updating ImplicitFunctionLine.
Arrays have incompatible sizes for this operation.
Any help would be appreciated, Thanks in advance
load ellipse % loads x and y
%least squares fit to an ellipse
% A x^2 + B xy + C y^2 + Dx + Ey = 1
% Returns coefficients A..F
%A x^2 + B xy + C y^2 + Dx + Ey + F = 0
% where F = -1
M = [x.^2 x.*y y.^2 x y]; % design matrix
b1=ones(size(x));
MTM=M'*M;MTb=M'*b1; %normal equation
R=rref([MTM MTb]); % the coefficent are found in the last collunm
A=R(1:6);
B=R(2,6);
C=R(3,6);
D=R(4,6);
E=R(5,6);
f= @(x,y) A.*x.^2 + B.*x.*y+C.*y.^2+D.*x+E.*y-1; % ellipse function
figure, plot(x, y, '.')
hold on
fimplicit(f)
1 个评论
Alex Sha
2022-4-21
Function: A*x^2 + B*x*y + C*y^2 + D*x + E*y + 1 = 0
Parameter:
A: -0.550741506585047
B: -0.46781995608367
C: -0.804115378029277
D: -0.163329836528614
E: 2.72555198327659
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/971710/image.jpeg)
采纳的回答
更多回答(1 个)
Matt J
2022-4-21
编辑:Matt J
2022-4-21
I feel like i have everything correct (i might not have)
Your ordinary least squares method is not ideal because your design matrix has stochastic errors in it (iterative total least squares is the gold standard). The method used by this toolbox is a bit better,
and also has utility functions to let you plot directly,
load ellipse
fitobj=ellipticalFit([x,y]')
fitobj =
ellipticalFit with properties:
center: [-0.9975 1.9968]
a: 3.0246
b: 1.9954
angle: -30.0868
plot(fitobj)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/972140/image.png)
0 个评论
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Get Started with Curve Fitting Toolbox 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!