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Super simple angle help! =(

Discussion in 'Mac Programming' started by Awesomeness, Mar 28, 2009.

  1. macrumors member

    Ok, I need to find the angle 'tween two points on a 2D plane. This would be the angle in comparison to vertical. For example,

    This is 0 degrees
    This is 45 degrees
    ||   //
    ||  //
    || //
    This is 90
    Yeah, I'm working with Java. Could some one post the equation, the pseudo code, or Java code?

  2. macrumors 68030


  3. macrumors 68040


    I really hope this isn't homework. I made an inner class myPoint to demonstrate, i assume you already have a point class in place that you could use/extend:

    public class testtrig {
      public static void main(java.lang.String args[]) {
        testtrig x = new testtrig();
        myPoint p1 = x.new myPoint(1000.,1.);
        myPoint p2 = x.new myPoint(0.,0.5);
        System.out.println("The result for p1 and p2 is: " + p1.getAngleInDegreesWith(p2));
        System.out.println("The result from origin of p1: " + p1.getAngleInDegreesWithOrigin());
      public class myPoint {
        double xCoor; //We'll let them default to protected, so we can act on other myPoints in methods
        double yCoor; 
        myPoint(double x,double y) {
          this.xCoor = x;
          this.yCoor = y;
        public double getX() { return xCoor;}
        public double getY() { return yCoor;}
        public double getSlopeWith(myPoint p) {
          return (java.lang.Math.abs(p.xCoor - xCoor) / java.lang.Math.abs(p.yCoor - yCoor));
        public double getAngleInDegreesWith(myPoint p) {
          return java.lang.Math.toDegrees(java.lang.Math.atan(this.getSlopeWith(p)));
        public double getSlopeWithOrigin() {
          return xCoor/yCoor;
        public double getAngleInDegreesWithOrigin() {
          return java.lang.Math.toDegrees(java.lang.Math.atan(this.getSlopeWithOrigin()));
    It isn't the most beautiful or best documented, but it should get you the angle in degrees. I didn't do any I/O, the main class is just to demonstrate the use of some of the functions. You would want to add error checking that the slope wasn't infinity/undefined, etc.


    Edit: I was guessing at which angle you wanted, exactly... i figured that if you were working with the origin and some point with positive x and y value the angle you'd want would be the one between the x-axis and the line segment between the two points. If that isn't what you want, it should be easy to adjust... it's all a little trig. I didn't want to calculate the line segment length for use, that's why i went with tangent. Someone might need to check my logic for negative x and y values. It's saturday.
  4. macrumors member


    No, it's not homework. Thanks!

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