how to find the right distance evaluation function of an ellipse
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I want to fit a 2D data set to an ellipse using the ransac algorithm . Therefore I use the an equation in polar coordinates, with the origin at the center of the ellipse and with the angular coordinate theta.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/366430/image.png)
ft = fittype( @(a,b,theta,r) (a*b)./sqrt((b*cos(theta)).^2+(a*sin(theta)).^2), 'independent', 'theta', 'dependent','r', 'coefficients', {'a','b'});
fitLineFcn = @(points) fit(points(:,1),points(:,2),ft ) % type function handle
evalLineFcn = ... % distance evaluation function
[modelRANSAC, inlierIdx] = ransac(points,fitLineFcn,evalLineFcn, sampleSize,maxDistance);
How can I compute distances from an ellipse to the data. The example doesnt help me at all.
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Answers (1)
Matt J
on 25 Sep 2020
6 Comments
Matt J
on 29 Sep 2020
How can I get your matrix ellipse equation in my fit() ?
Once you have fitted the ellipse, you have the major and minor axes lengths a and b. Assuming you convert your data to a cartesian coordinate system in which the major axis is the x-axis, the A matrix will be given by
A=[1./a.^2, 0;0 1./b.^2];
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