Angles between points and a point different from the origin of axis?

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Davide Mori 2020-12-13

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回答： Mahesh Taparia 2020-12-16

Hi everyone,

If I have the origin of axis in (0,0) and I want to calculate the angle of different lines connecting some points to the origin I would write:

orig = [0 0];

rz(:,1)=(points(:,1)- orig(:,1));

rz(:,2)=(points(:,2)- orig(:,2));

alpha_i = atan2(rz(:,2), rz(:,1));

BUT what if I want to calculate the angles just changing the origin? That is, I have for example p = [-0.5 0] and I want to calculate the angles formed by the x-axis and the points but considering a point p different from the origin. Thank you!

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Answer 1

Mahesh Taparia 2020-12-16

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Hi

The similar approach can be used to find the angle which you already mentioned in the question. Moreover, the point 'p' (p = [-0.5 0]) also lies on the x axis, so its angle with x axis is 0.

In general, the equation of x axis is y=0. So the angle with x axis (y1=0) and any point (x2,y2) can be written as

theta=atan2(y2/(x2-x1))