Question

Im trying to find out the angle (in degrees) between two 2D vectors. I know I need to use trig but I’m not too good with it. This is what I’m trying to work out (the Y axis increases downward):

I’m trying to use this code at the moment, but it’s not working at all (calculates random angles for some reason):

private float calcAngle(float x, float y, float x1, float y1)
{
    float _angle = (float)Math.toDegrees(Math.atan2(Math.abs(x1-x), Math.abs(y1-y)));
    Log.d("Angle","Angle: "+_angle+" x: "+x+" y: "+y+" x1: "+x1+" y1: "+y1);
    return _angle;
}

These are my results (There constant when providing a constant position, but when I change the position, the angle changes and I can’t find any link between the two angles):

Position 1:
x:100 y:100
x1:50 y1:50
Angle: 45

Position 2:
x:92 y:85
x1:24 y1:16
Angle: 44.58

Position 3:
x:44 y: 16
x1:106 y1:132
Angle: 28.12

Edit: Thanks everyone who answered and helped me figure out that was wrong! Sorry the title and the question was confusing.

Answer 1

Aha! Turns out I just needed to flip my angle and use atan2. This is my final code:

private float calcAngle(float x, float y, float x1, float y1)
{
    float _angle = (float)Math.toDegrees(Math.atan2(x1-x, y-y1));
    return _angle;
}

Thanks everyone for helping me figure this out and also for helping me to understand what I’m actually doing! 🙂