ellipse fitting from a plot in MATLAB

I have datapoints in text file which I have imported and ploted. Now I want to do ellipse fitting of that data. Can you please help me with that?

Answer 1

[Image Analyst]

See my attached ellipse fitting demo.

Also see the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_fit_an_ellipse_or_other_shape_to_a_set_of_XY_data.3F

[Sayanta Goswami]

Thanks for your answer.

I already have data files.

here I have attached .m file and .txt file as well. Can you please suggest how can I do ellipse fitting in my code?

[Image Analyst]

What do a and b represent? Why are they different lengths?

Your code doesn't seem to show any ellipses. What's going on?

[Sayanta Goswami]

can you please check it now?

[Sayanta Goswami]

a and b are the two waves one is sine and another is cosine

[Image Analyst]

Are you sure you actually tried to adapt my demo? Anyway, it was rather straightforward and you just needed to add a call to fitellipse() at the end of your code. It's attached and produces this plot.

[Sayanta Goswami]

Thanks a lot. I had seen the code but there was some issue with these two files that I have attached herewith.It is not giving Theta value correctly. Theta should come araound zero degree but it is giving 68 degree and 44 degree. Please help me.

I have attached google drive link for the files and the code that I was using.

https://drive.google.com/file/d/1GkB5iX4-N0cfqB5FMG78h7YUU7CIu1LM/view?usp=sharing

https://drive.google.com/file/d/1GkB5iX4-N0cfqB5FMG78h7YUU7CIu1LM/view?usp=sharing

Answer 2

[Matt J]

Theta should come araound zero degree but it is giving 68 degree and 44 degree.

Using ellipticalFit() in,

https://www.mathworks.com/matlabcentral/fileexchange/87584-object-oriented-tools-for-fitting-conics-and-quadrics

[X,Y]=deal( smoothX(jdx:jdx+200000,1),smoothY(idx:idx+200000,1) );

fitobj=ellipticalFit([X,Y].')

[hFit,hData]=plot(fitobj,{'Color','r','LineWidth',3},{'SizeData',2});
xlabel 'X'
ylabel 'Y'
legend([hFit,hData],'Fit','Data')

gives me and angle of about 79 degrees (or 11 degrees to the Y axis). I don't know how close to zero degrees you expected, but the tilt angle in your samples is very visible, so it couldn't be too close.

fitobj = 

  ellipticalFit with properties:

    center: [-0.0156 -0.0130]
         a: 0.5679
         b: 0.4198
     angle: 79.2091