transform x,y coordinate to angle

Hi Guys,

I'm struggeling with this problem in which I have two points (x and y coordinates known) that move independent of eachother. I need to find the angle between these two points wrt North. The angle can be between -180:180. As indicated in the Figure I added, I would like to find the "red angle", but by using the sin,cos,tan equations I can only get the "blue angle".

Anyone that knows how to tackle this problem? It needs to work for all respective locations of both points to one another...

I tried the following code, but that does only result in the blue angle as expected...

heading_s=atand((y_ip-y_s)/(x_ip-x_s));

Answer 1

[Jon]

I would think that you could use atan2 or atan2d (if you want result in degrees) for this.

For example

x1 = [2;1] % first point
x2 = [-1;-1] % second point
delta = x2 - x1 % vector that points from x1 to x2
heading = atan2d(delta(2),delta(1))
 

which results in

heading =

-146.3099

[Jon]

edited above,originally I had arguments in reverse order

[Jon]

If you want the heading to give conventional compass reading (N = 0, E = 90, S = 180, W = 270 you can use

heading = atan2d(delta(2),delta(1))
compassHeading = mod(90-heading,360)