Circle Fit at the Corner of the Step??

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Swati Jain
Swati Jain el 15 de En. de 2018
Comentada: Swati Jain el 22 de En. de 2018
Hi,
I have a step curve (figure 1) and I want fit a circle to each corner of step (shown in figure 2). I wrote the following function for the circle fit:
function [xc,yc,R]=circfit(x,y)
x=x(:); y=y(:);
a=[x y ones(size(x))]\-(x.^2+y.^2);
xc=-0.5*a(1);
yc=-05*a(2);
R=0.5*sqrt((a(1)^2+a(2)^2)-4*a(3));
end
I read the corners coordinates manually and apply the following code to fit circle
y=C(1050:1100); % C is array of step
x=1050:1100;
[xc,yc,Re] = circfit(x,y);
I got the values of center and radius of circle, which are looking way to higher than I except and I don't understand how to plot this fitted circle. If I plot using
plot((x-xc).^2+(y-yc).^2-Re.^2)
It is same as the corner of the step. Could any one tell me that if approach is correct or not and how to plot fitted curve that I can show it in same way as shown in fig. 2? Is there any other way to find circle fit?
%

Respuestas (2)

Darshan Ramakant Bhat
Darshan Ramakant Bhat el 18 de En. de 2018
This is due to the different scaling of the axes. If you observe y axes varies from 0 to 1, while x axes varies from 0 to 2000. MATLAB automatically fits the aspect ration of the axes for the visualization purpose. You have to limit the x-axes range to view the circle.
Please refer to the below code:
clc;
clear all;
close all;
t = 1 : 2000;
sf = t>1000;
figure(1);
plot(t,sf);
xlim([1000 1002])
c = [1001.05,0.95];
r = 0.05;
hold on;
%Inbuilt function in image processing toolbox to plot the circle.
viscircles(c,r);
I hope this will help you.
  2 comentarios
Swati Jain
Swati Jain el 18 de En. de 2018
Thanks for your response. viscirles is working well. But my other problem is still not solved. My problem is that radius obtained from circfit function is way to higher than I expect and even if I limit the x-axis in my plot there is no change, since MATLAB is adjusting the axes according to the radius of the circle. I am not sure what is wrong with my function, however, I found similar function on google. If there is any other way to fit a circle please let me now. Attached is the image what I am getting as after circle fit.
Darshan Ramakant Bhat
Darshan Ramakant Bhat el 19 de En. de 2018
I am not sure what you are trying to do in circfit() function. Can you elaborate on your logic ?

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Darshan Ramakant Bhat
Darshan Ramakant Bhat el 19 de En. de 2018
I guess there is something wrong going on in estimating the radius of curvature using the x,y points. Please refer below code to do the same:
I hope this will help you.
Regards,
Darshan
  1 comentario
Swati Jain
Swati Jain el 22 de En. de 2018
Hi,
This function is giving same result as I got from my function. Thanks!

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