Find angle between dots
78 views (last 30 days)
Show older comments
Hi all,
I need to calculate the angle between (imaginary lines) connecting dots on an image.
Below is an example of the bw image that I have:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/153695/image.png)
And I want to calculate the angle as shown below:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/153696/image.png)
Thank you
0 Comments
Answers (3)
Roger Stafford
on 15 Dec 2013
The matlab function 'atan2' can be used to accomplish this. It is more accurate for this purpose than 'acos'. Let P0 = [x0;y0] be a vector of x,y coordinates for the vertex of the angle to be measured and P1 = [x1;y1] and P2 = [x2;y2] be vectors for points on the two lines connecting them to P0.
x10 = x1-x0;
y10 = y1-y0;
x20 = x2-x0;
y20 = y2-y0;
ang = atan2(abs(x10*y20-x20*y10),x10*y10+x20*y20);
The angle 'ang' will be in radians.
0 Comments
Youssef Khmou
on 15 Dec 2013
hi, Computing the angle require the scalar product between the points, so you need to know the coordinate of the white dots, here is an example
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/174099/image.jpeg)
the image above is generated by :
T=zeros(200);
T(10,10)=1;
T(40,50)=1;
T(60,30)=1;
imshow(T)
Let us compute the Euclidean norm of the vectors :
ab=sqrt((50-10)^2+(40-10)^2)
ac=sqrt((30-10)^2+(60-10)^2)
You can obtain the angle by :
acos(dot([10 60],[10 40])/(ac*ab))*180/pi
1 Comment
Walter Roberson
on 20 Sep 2015
TAEYUN commented
if i want to find angle of btween kneejoint and hipjoint, how can i do? just i knew only x,y,z values of joints... help me plz..
See Also
Categories
Find more on Geometric Transformation and Image Registration in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!