points are clockwise - Java java.lang

Java examples for java.lang:Math Algorithm

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Description

points are clockwise

Demo Code


//package com.java2s;

import java.awt.*;

import java.util.ArrayList;

public class Main {
    /**//from  ww w . j a va 2s.c  om
     * points are clockwise
     * @param points
     * @return
     */
    public static ArrayList<Double> getAngleFromPoints(
            ArrayList<Point> points) {
        ArrayList<Double> angleList = new ArrayList<Double>();
        ArrayList<Point> tmpPoints = points;
        tmpPoints.add(0, points.get(points.size() - 1));
        tmpPoints.add(tmpPoints.size() - 1, points.get(0));
        int size = tmpPoints.size();
        for (int i = 1; i < size - 1; ++i) {
            double angle = getAngle(tmpPoints.get(i), tmpPoints.get(i - 1),
                    tmpPoints.get(i + 1));
            angleList.add(angle);
        }
        return angleList;
    }

    /**
     * calc the the angle of <BAC by using vector method
     * @param ptA
     * @param ptB
     * @param ptC
     * @return
     */
    public static double getAngle(Point ptA, Point ptB, Point ptC) {
        double angle = 0;
        // vector AB
        double Vab_x = ptB.x - ptA.x;
        double Vab_y = ptB.y - ptA.y;

        // vector AC
        double Vac_x = ptC.x - ptA.x;
        double Vac_y = ptC.y - ptA.y;

        double productValue = Vab_x * Vac_x + Vab_y * Vac_y;
        double Vab_value = Math.sqrt(Math.pow(Vab_x, 2.0)
                + Math.pow(Vab_y, 2.0));
        double Vac_value = Math.sqrt(Math.pow(Vac_x, 2.0)
                + Math.pow(Vac_y, 2.0));

        double cosValue = productValue / (Vab_value * Vac_value);
        //casValue [-1,1]
        if (cosValue < -1 && cosValue > -2) {
            cosValue = -1;
        } else if (cosValue > 1 && cosValue < 2) {
            cosValue = 1;
        }

        angle = Math.acos(cosValue) * 180 / Math.PI;
        return angle;
    }
}

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