Get intersection of two segments

Hi,

I have these two following matrices:

Can you help me with some way to check if every line from segmentBA intersects every line from obstacleMatrix?

Every line in both matrices represent a segment defined as: [x1 y1 x2 y2] (x1,y1)----(x2,y2)

I don't want to know exactly the intersection point, just only true if the intersection exists or false.

[darova]

for loop and polyxpoly? Did you think about this?

[pb1106]

Well, I am aware of the function but I want the code to be adaptable to other programming language because I want this code to be integrated in a control algorithm for a 2 DOF robot.

So, if you have some idea without polyxpoly I will be grateful

Answer 1

[darova]

Here is a script

It solves line-line intersection (x1,y1) - line1, (x2,y2) - line2

a1 = (y1(i+1)-y1(i)) / (x1(i+1) - x1(i));
b1 = y1(i) - a1*x1(i);
a2 = (y2(j+1)-y2(j)) / (x2(j+1) - x2(j));
b2 = y2(j) - a2*x2(j);
X = (b1-b2)/(a2-a1);

Then just checks if intersection point lies on both lines

cond1 = x1(i) < X && X < x1(i+1);
cond2 = x1(i) > X && X > x1(i+1);
cond3 = x2(j) < X && X < x2(j+1);
cond4 = x2(j) > X && X > x2(j+1);
if ( cond1 || cond2 ) && ( cond3 || cond4 )  
    % do stuff
end

[Matthew Boyd]

Does this work for all line segment - line segment intersection? It does not assume infinite lines right?

Answer 2

[Image Analyst]

Are the lines in rows or columns? Anyway, just take a line from each and subtract them and see if the signs are all the same:

if length(unique(sign(vec1-vec2))) == 1
	% No crossing
	fprintf('They do not cross or they completely overlap.\n');
else
	% Crossing
	fprintf('They cross or intersect.\n');
end

where vec1 and vec2 are the signals.