How to find the coordinate of the intersection multiple lines?

If i have lines drawn on an image, how can I find the coordinate of the intersection of the lines? (multiple lines are intersecting)

Answer 1

[KSSV]

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

[Misha Patel]

Hi, thanks. you actually helped me to draw the lines:

https://uk.mathworks.com/matlabcentral/answers/348170-drawing-lines-and-perpendicular-lines-on-a-photo-in-matlab

This function returns the intersection of the curves L1 & L2 that exist as 2 row matrices.

[KSSV]

Not only curves....it will give intersection of lines also.

[Misha Patel]

Okay, but I have labelled my my lines L1 and L2, as so:

L1=line([mean(x) mean(x)-L],[mean(y) mean(y)-L*minv],'Color','g')
L2=line([mean(x) mean(x)-L],[mean(y) mean(y)-L*minv],'Color','g')

I then call the function like this:

P=InterX(L1,L2)

but I am getting an error, am I calling the function wrong?

[KSSV]

Note that line plots the given coordinates..it is a graphic object. YOu need to pass the coordinates into the function.

P1 = rand(2,2) ;
P2 = rand(2,2) ;

figure(1)
hold on
plot(P1(1,:),P1(2,:),'r') ;
plot(P2(1,:),P2(2,:),'b') ;

% get intersection
P = InterX(P1,P2) ;
if ~isempty(P)
    plot(P(1),P(2),'*k')
end

[Misha Patel]

in the case you have shown, P1 and P2 are arrays. My line is a drawn between 2 coordinates.... how would I get an array out of this?

[KSSV]

You are providing....data points to line....

[Image Analyst]

If you need the data at any arbitrary point, you have the two end points and can compute the line formula, so you have everything you need. If you want digitized/quantized coordinates, you can round the double numbers or you can look at Bresenham's line algorithm: https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm

Answer 2

[Image Analyst]

Use bwmorph() and ask for branchpoints on your skeletonized binary image.

crossings = bwmorph(binaryImage, 'branchpoints');

binaryImage should have only single pixel wide lines in it. Threshold it and call bwmorph(binaryImage, 'skel', inf) if you need to.

binaryImage = grayImage < 150; % Whatever...
skeletonImage = bwmorph(binaryImage, 'skel', inf); % Thin down to one pixel wide lines.
crossings = bwmorph(skeletonImage, 'branchpoints');

Also, see Steve's blog: http://blogs.mathworks.com/steve/2016/04/12/intersecting-curves-that-dont-intersect/