Hi everyone,

I was using the following formula to find the angle between three coordinate values (i.e., P1, P0, P2; finding angle at P0)

ang = (180/pi)*(atan2(abs(det([P2-P0;P1-P0])),dot(P2-P0,P1-P0)));

formula taken from: https://in.mathworks.com/matlabcentral/answers/57736-how-to-calculate-degree-between-3-points-in-matlab#answer_69886

So, it worked fine when I took the coordinate values as ;

P0 = [3,1];
P1 = [1,3];
P2 = [4,4];
figure;
plot(P0(1),P0(2),"*"); hold on;
plot(P1(1),P1(2),"*"); hold on;
plot(P2(1),P2(2),"*"); hold on;
ylim([0 7])
xlim([0 5])
legend("P0","P1","P2")
% P0 is the center where the angle would be
ang = (180/pi)*(atan2(abs(det([P2-P0;P1-P0])),dot(P2-P0,P1-P0))); % formula to get angle
% ang = 63.439 deg

But when I took three coordinate values as the following then it gave me a strange angle value, which is probably the supplmentary angle at P0.

P1 = [-16.49,-17.69];
P0 = [-25.83,-21.73];
P2 = [-40.77,-18.10]
figure;
plot(P0(1),P0(2),"*"); hold on;
plot(P1(1),P1(2),"*"); hold on;
plot(P2(1),P2(2),"*"); hold on;
legend("P0","P1","P2");
ang = (180/pi)*(atan2(abs(det([P2-P0;P1-P0])),dot(P2-P0,P1-P0)));
% ang = 142.9526 deg ; seems like the supplementary angle at P0.

Why is it happening? Any clues?

I need to apply this formula to calculate angle over 100s of coordinates and but if this kind of non-uniformity would happen then I wouldn't be able to use it.

Any help would be appreciated!

Thank you.

I have also asked in the Matlab community at Mathworks:

https://in.mathworks.com/matlabcentral/answers/1793970-error-in-finding-the-angle-between-three-points-using-atan2

Beginner to excel here. I usually use Matlab for my calculations but for this particular project Excel has proven easier (until now).