Angle between two points

Question

I need to get angle between two points on the flat(x,y), for example I have points A and B, point A have directions(90), how could I count angle between points A and B from A directions in Java?

Here's an image for example:

enter image description here

Have you considered that tan(θ) = height of B/length of B? I agree that this is more math. If you're stuck on implementation, maybe you should phrase it that way. — , Jul 27 '14 at 21:21
This question appears to be off-topic because it is about Math — Vincent Mimoun-Prat, Jul 27 '14 at 21:23
possible duplicate of [Java: Calculating the angle between two points in degrees](http://stackoverflow.com/questions/9970281/java-calculating-the-angle-between-two-points-in-degrees) — BitNinja, Jul 27 '14 at 21:27
This is a basic trigonometry problem -- really has nothing to do with programming. — Hot Licks, Jul 27 '14 at 21:38

imulsion · Answer 1 · 2014-07-27T21:30:02.783

Math.toDegrees(Math.atan(Math.abs(pointBY - pointAY), Math.abs(pointBX - pointAX)));

This calls the inverse tangent function to find an angle based on the lengths of the opposite and adjacent sides of a right angled triangle. However, you should add this if statement:

if(!(pointAX == pointBX || pointAY == pointBY))
{
angle = Math.toDegrees(Math.atan(Math.abs(pointBY - pointAY), Math.abs(pointBX - pointAX)));
}

Otherwise you can cause an exception because the tan function breaks down if the angle is 90 or 0 degrees.

pointAX and pointBX are the X coordinates of the points, while pointAY and pointBY are the Y coordinates of the points.

This function finds the absolute value of the difference between the coordinates (so the length of the opposite and adjacent sides of the right-angled triangle formed from the two points) and then performs the inverse tan function on them, finding the angle.

Thank you, I understood, how to get angle between A and B points, but I don't understand how get angle between AB angle and A direction, here's small example what I need there is 3 points A1,A2 and B, points A has direction, image: http://cs614922.vk.me/v614922073/13f87/a3d26coYe-4.jpg — Martin Gut, Jul 28 '14 at 16:21
Please not that the code above is incorrect. java.lang.Math.atan does not take in two variables. The author meant to use atan2 instead. — EndOfAll, Mar 05 '20 at 18:22

Angle between two points

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