Geometries.java :  » UnTagged » educationalrobots » oursland » math » Android Open Source

package oursland.math;

import java.awt.geom.Point2D;

public class Geometries {
  public static double getAngleCosine(Point2D p1, Point2D p2, Point2D p3) {
    final double dx1 = p1.getX() - p2.getX();
    final double dy1 = p1.getY() - p2.getY();
    final double dx2 = p3.getX() - p2.getX();
    final double dy2 = p3.getY() - p2.getY();
    final double value = dy1 * dx2 - dx1 * dy2;
    return value;
  }

  public static double getAngle(double dx, double dy) {
    double h = Math.sqrt(dx * dx + dy * dy);
    double theta;
    // use the smaller value for the more precise angle
    if(Math.abs(dx) > Math.abs(dy)) {
      theta = Math.asin(dy / h);
      if(dx < 0) {
        theta = Math.PI - theta;
      }
    } else {
      theta = Math.acos(dx / h);
      if(dy < 0) {
        theta = UsefulConstants.TWOPI - theta;
      }
    }
    if(theta > Math.PI) {
      theta -= UsefulConstants.TWOPI;
    }
    if(theta < -Math.PI) {
      theta += UsefulConstants.TWOPI;
    }
    return theta;
  }
}