Find point of intersection between two vectors in MATLAB

Question

I have a very simple MATLAB question. What is the easiest way to find the point of intersection between two vectors. I am not familiar with the various MATLAB functions -- it seems like there should be one for this. For example, if I have one vector from (0,0) to (6,6) and another vector from (0,6) to (6,0), I need to determine that they intersect at (3,3).

Accepted Answer

One solution is to use the equations derived in this tutorial for finding the intersection point of two lines in 2-D (update: this is an internet archive link since the site no longer exists). You can first create two matrices: one to hold the x coordinates of the line endpoints and one to hold the y coordinates.

```
x = [0 0; 6 6];  %# Starting points in first row, ending points in second row
y = [0 6; 6 0];
```

The equations from the above source can then be coded up as follows:

```
dx = diff(x);  %# Take the differences down each column
dy = diff(y);
den = dx(1)*dy(2)-dy(1)*dx(2);  %# Precompute the denominator
ua = (dx(2)*(y(1)-y(3))-dy(2)*(x(1)-x(3)))/den;
ub = (dx(1)*(y(1)-y(3))-dy(1)*(x(1)-x(3)))/den;
```

And you can now compute the intersection point of the two lines:

```
xi = x(1)+ua*dx(1);
yi = y(1)+ua*dy(1);
```

For the example in the question, the above code gives `xi = 3` and `yi = 3`, as expected. If you want to check that the intersection point lies between the endpoints of the lines (i.e. they are finite line segments), you just have to check that the values `ua` and `ub` both lie between 0 and 1:

```
isInSegment = all(([ua ub] >= 0) & ([ua ub] <= 1));
```

A couple more points from the tutorial I linked to above:

- If the denominator `den` is 0 then the two lines are parallel.

- If the denominator and numerator for the equations for `ua` and `ub` are 0 then the two lines are coincident.

Find point of intersection between two vectors in MATLAB

Solution

Problem