Find angle in degrees from one point to another in 2D space? Given Point A and Point B in 2D space, how can I find the angle Point B is from Point A? 0° can be any direction; it doesn't matter. For example, Point A is at (0, 10) and Point B is at (10, 20). The angle is 45° in this example (assuming 0° is up).
 A: I believe that the accepted answer does not correctly solve the problem for many people visiting this question. I am doing 2D simulations and the answer above does not solve my problem. Imagine the following circle:
$\hskip1.8in$
Assume that the middle of the circle is point A. Point B is at some angle from A according to the angles of the circle (so 0°) is right.
$\hskip2in$The atan2 function is what you need!
$$ atan2(y, x) $$
$\hskip3.2in$ Where
$$ y = y_B - y_A $$
$$ x = x_B - x_A $$
Read more about it here.
A: From what I understood about your question, you want to find the angle between two points given their coordinates. In that case, first find the slope of the line using the slope formula:
$$m=\dfrac{y_2-y_1}{x_2-x_1}$$
where $(x_1,y_1)$ and $(x_2,y_2)$ are coordinates on the line. Next, use this formula:
$$\tan(\theta)=m$$
where $\theta$ is the angle. Therefore, the angle $\theta$ equals:
$$\theta=\tan^{-1}(m)$$

Let's use the points $(0,10)$ and $(10,20)$ as an example (you mentioned it in your question). The slope is:
$$m=\dfrac{10-20}{0-10}$$
$$m=\dfrac{-10}{-10}$$
$$m=1$$
Now we will find $\theta$.
$$\tan(\theta)=1$$
$$\theta=\tan^{-1}(1)$$
$$\theta=45^\circ$$

Note: The $\tan(\theta)=m$ formula only gives the angle facing the positive $x$-axis (i.e. facing the "right"). So for a negative slope, you should get an angle that is greater than $90^\circ$.
