Find intersection points between a line and a boundary

I am trying to find the intersection points between a line and a boundary, how can I do it?

Code:

clc;
clear;
close all;
 
url='https://cdn.pixabay.com/photo/2012/04/01/17/05/brazil-23548_960_720.png';
I = imread(url);
I = rgb2gray(I);
[yDim,xDim] = size(I);
 
if yDim>xDim
    lineLength = yDim;
else
    lineLength = xDim;
end

imshow(I);
hold on;
axis on;
%Boundary
BW = imbinarize(I);
[B,L] = bwboundaries(BW,'noholes');

k=1;
stat = regionprops(I,'Centroid');
b = B{k};
c = stat(k).Centroid;
yBoundary = b(:,2);
xBoundary = b(:,1);
 
centroidy = c(:,2);
centroidx = c(:,1);
plot(yBoundary, xBoundary, 'g', 'linewidth', 2);
 
angle = 270;
xLine(1) = centroidx;
yLine(1) = centroidy;
xLine(2) = xLine(1) + lineLength * cosd(angle);
yLine(2) = yLine(1) - lineLength * sind(angle);
plot(xLine, yLine);

Answer 1

[KSSV]

Try this one:

https://in.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections?focused=5165138&tab=function

[Ali razi]

I added this line :

P = InterX([yBoundary ;xBoundary], [xLine; yLine])

and I got this error:

Error using bsxfun
Non-singleton dimensions of the two input arrays must match each other.

Error in InterX (line 63)
    C1 = feval(hF,D(bsxfun(@times,dx1,y2)-bsxfun(@times,dy1,x2),S1),0);

Error in plotAngleLineOverOutlineTemp (line 42)
P = InterX([yBoundary ;xBoundary], [xLine; yLine])

What did I do wrong?

[KSSV]

Check the inputs to InterX....they should be of size 2*m. Read about the function examples given in the function.

[Ali razi]

So it:

P = InterX([rot90(yBoundary) ;rot90(xBoundary)], [(xLine); (yLine)])

Thanks

[KSSV]

Why rot90? You need to make the array column major. If x and y are your corodinates of a curve/ line.

If x and y are row vectors.

L1 = [x ; y] ; 

If x and y are column vectors.

L1 = [x y]' ; 

[Ali razi]

The first thing that popped in my mind. The results are the same. Any issue why not use rot90?

[KSSV]

It just needs a transpose......so we transpse using '.