How do you find the points where a line crosses over itself?

I have a set of XY coordinates and I need to identify the number and location of where the line intersects itself. I've plotted an example below.

The following code worked, but I'm concerned the thresholding input to unique tol may cause false positives.

[C,iz,ic]=uniquetol(Z,.03,'ByRows',true);
L=setdiff(Z,C,'rows','stable');
figure;plot(Z(:,1),Z(:,2));hold on; scatter(L(:,1),L(:,2))

For example, below is .03

And this was set at .04

The data were collected at the same frame rate, but the object being tracked exhibited variable velocity. Anyone have any idea how to determine threshold for a specific velocity? Or perhaps another method that is less error prone in general?

Any help/input is much appreciated!

[Walter Roberson]

I wonder if these could help?

https://www.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections

https://www.mathworks.com/matlabcentral/fileexchange/11837-fast-and-robust-curve-intersections

Answer 1

[KSSV]

load XY.mat ;
x = A(:,1) ; y = A(:,2) ;

P = InterX([x y]') ;

plot(x,y,'b') ;
hold on
plot(P(1,:),P(2,:),'*r')

Download the file InterX from the link: https://in.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections

[Laura Berkowitz]

Thank you! Works perfectly!