How to find angle between two lines?

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For example, there is line L1 between two points (x1,y1) and (x2,y2). Another line L2 between points (x1,y1) and (x3,y3). I want to find the angle between the lines L1, L2. How to find in MATLAB? I think in matlab there is no predefined function which performs the same.

Accepted Answer

Bjorn Gustavsson
Bjorn Gustavsson on 21 Oct 2019
A more stable method that what Jos suggested is
v_1 = [x2,y2,0] - [x1,y1,0];
v_2 = [x3,y3,0] - [x1,y1,0];
Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2));
HTH
  3 Comments
jari jafri
jari jafri on 4 Oct 2023
Edited: jari jafri on 4 Oct 2023
I got my V_1 and V_2 vectors as
v_1 =
1×3 int32 row vector
-633 990 0
v_2 =
1×3 int32 row vector
0 500 0
But i am having the following error so I 'm looking for how to remove this error
Error using norm
First argument must be single or double.
Error in test6 (line 64)
Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2));
I'm getting this error while using this code
Dyuman Joshi
Dyuman Joshi on 4 Oct 2023
@jari jafri convert the data to double -
v_1 = int32([-633 990 0]);
v_2 = int32([0 500 0]);
v_1 = double(v_1);
v_2 = double(v_2);
Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2))
Theta = 0.5689

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More Answers (2)

Jos (10584)
Jos (10584) on 21 Oct 2019
Use the dot product between the two vectors (v1 and v2) given by the four x,y pairs points.
Given the formula: dot(v1,v2) = | v1 | x | v2 | x cos(A)
I leave it to you to find the angle A using the matlab functions norm, dot and acos.

Bjorn Gustavsson
Bjorn Gustavsson on 21 Oct 2019

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