# Developers Planet

TheMintyMate February 2016

### Getting the angle from a direction vector?

I have this simple function to set an angle for a vector. It effectively gets the vector's current magnitude (length), calulates the angle and converts the angle from radians to degrees. Then I apply the angle to X and Y, lastly multiplying the vector by it's original magnitude.

``````this.setAngle = function(degree){
var l = this.length();  //magnitude of vector
var angle = degree*Math.PI/180; //degress converted to radians
this.x=Math.cos(angle);
this.y=Math.sin(angle);
this.multiply(l);  //original magnitude
return;
}
``````

However I am unsure how to obtain (get) an angle from a Vector. Below is my attempt:

``````this.getAngle = function(){
var degrees = angle/(180*Math.PI);  //degrees
return Math.floor(degrees); //round number, avoid decimal fragments
}
``````

This attempt doesn't return any value except 0 or -1.

Any suggestions?

Edit:

Correct method:

``````this.getAngle = function(){
var angle = Math.atan2(this.y, this.x);
var degrees = 180*angle/Math.PI;
return (360+Math.round(degrees))%360;
}
``````

Gavriel February 2016

``````this.getAngle = function(){
var angle = Math.atan2(this.y, this.x);   //radians
// you need to devide by PI, and MULTIPLY by 180:
var degrees = 180*angle/Math.PI;  //degrees
return (360+Math.round(degrees))%360; //round number, avoid decimal fragments
}
``````