Calculates the north relative clockwise orientation of a line.

line direction N CW

/*

The MIT License

Copyright (c) 2010 Aaron Dandy ([email protected]) 

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

*/

/*
Function: lineDirection

Calculates the north relative clockwise orientation of a line.

Parameters:

ax - The x-coordinate of the first point defining a line.
ay - The y-coordinate of the first point defining a line.
bx - The x-coordinate of the second point defining a line.
by - The y-coordinate of the second point defining a line.

Returns:

The direction of the line or Number.NaN on failure.
*/
var lineDirection = function (ax, ay, bx, by) {
    var dx = bx - ax;
    var dy = by - ay;
    var m = Math.sqrt((dx * dx) + (dy * dy));
    return m ? Math.atan2(dx / m, dy / m) : Number.NaN;
}
var radiansToDegrees = function (r){
    return 180 * r / Math.PI;
}
var noNegDegrees = function(d){
    while(d < 0){
        d += 360;
    }
    return d;
}
alert(noNegDegrees(radiansToDegrees(lineDirection(4, 3, 2, 1))));

Hi there! I am really interested in using this code, but I'm not getting which language is it based on (I'm not an experet in this...). If You could please enlight me I would be very happy! Thanks in advance, cheers.

That code is JavaScript but it should be easy to translate to any language as it is a simple function.

Thanks but a much better solution would be the one presented here .
This doesn't work in a reliable manner.

This doesn't work in a reliable manner.

What inputs reproduce the bug and what are the expected outputs?

I don't think atan2 requires normalization so some floating point error may be introduced, maybe that is what you mean 🤷‍♂️

have you tried something like line((0,0), (256,0))

I get 90 in my browsers as that would be 90 degrees clockwise from north. What did you get?

Interesting, this actually crashed on my side!
Edit:
Thanks a lot, yes, it works fine, the issue was in my own code.