Find angle between dots
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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
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回答(3 个)
Roger Stafford
2013-12-15
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.
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Youssef Khmou
2013-12-15
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
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Walter Roberson
2015-9-20
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..
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