get the inflection points of a contour

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Sylvain Ard
Sylvain Ard am 25 Jun. 2020
Beantwortet: Sylvain Ard am 30 Jun. 2020
Hello,
I want to find the inflexion points of a contour made by adjacents pixels.
An example of contour can be find here : http://sylvain-ard.fr/temp/cnt.csv
It must delete noise (small inflexions).
Please help me
Thank you
The image of the example contour is here :
  2 Kommentare
Kanika Gupta
Kanika Gupta am 25 Jun. 2020
I think you can find a solution here :
  1. https://www.mathworks.com/matlabcentral/answers/131760-how-to-find-contour-inflection-points?s_tid=answers_rc1-2_p2_MLT
  2. https://www.mathworks.com/matlabcentral/answers/385053-how-to-find-a-number-of-inflection-points-in-a-contour?s_tid=answers_rc1-1_p1_MLT
Sylvain Ard
Sylvain Ard am 25 Jun. 2020
I have already tested these solutions but they're don't work with my example, the result is too bad with every filtering method

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Antworten (2)

darova
darova am 28 Jun. 2020
Here is a start:
  • use boundary function to find (x,y) coordinates of your contour (and order)
  • Smooth the curve: reduce points and interpolate the data using this 3d interpolation
  • use cross product to find inflection points
simple example
x = 0:0.2:10;
y = sin(x).*x.^2;
dx = diff(x)';
dy = diff(y)';
v0 = dx(2:end)*0;
a1 = [dx(1:end-1) dy(1:end-1) v0];
b1 = [dx(2:end) dy(2:end) v0];
n = cross(a1,b1,2);
ix = find( diff(sign(n(:,3))) );
plot(x(ix),y(ix),'or')
line(x,y)

Sylvain Ard
Sylvain Ard am 30 Jun. 2020
finally I succeeded with the function approxPolyDP of OpenCV not Matlab function

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