# I want to find out how to get the angles between the centroids

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Don Wirasinha on 26 Jan 2023
Answered: Image Analyst on 26 Jan 2023
I have got the code which detects blue colored objects, shows their centroids and draws a line through them. My next task is to display the angle displayed between the centroids. (the angle formed at the elbow joint, with the centroids being located at the shoulder, elbow and wrist. if you could find the code required for this and can explain it a bit it would be helpful.
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Matt J on 26 Jan 2023
In what way is displaying the angle a different challenge from what you've already displayed? It's just one more number to add to the image isn't it?

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### Answers (2)

Askic V on 26 Jan 2023
Hello Don,
I think you might find this example useful:
close all
clc
clear
P1 = [231; 84];
P2 = [297; 284];
P3 = [544; 250];
p_12 = P1-P2;
p_23 = P3-P2;
theta = acosd(dot(p_12,p_23)/(norm(p_12)*norm(p_23)))
theta = 100.4253
% Plot results
plot(P1(1),P1(2),'ro');
text(P1(1),P1(2),[' \leftarrow ', num2str(P1(1)),', ', num2str(P1(2))]);
hold on
plot(P2(1),P2(2),'ro');
text(P2(1),P2(2),[' \leftarrow ', num2str(P2(1)),', ', num2str(P2(2))])
plot(P3(1),P3(2),'ro');
text(P3(1),P3(2),[' \leftarrow ', num2str(P3(1)),', ', num2str(P3(2))])
v1 = quiver(P2(1),P2(2), -abs(P2(1)-P1(1)), -abs(P2(2)-P1(2)),'off');
v2 = quiver(P2(1),P2(2), abs(P3(1)-P2(1)), -abs(P3(2)-P2(2)),'off');
grid on
xlim([0 700])
ylim([0 300])
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Image Analyst on 26 Jan 2023
Try title or text on the image axes:
caption = sprintf('Angle = %.2f degrees', theta);
title(caption, 'FontSize', 16);
text(350, 175, caption, 'Color', 'r', 'FontSize', 16);
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