calculate the the angle of lines - Java 2D Graphics

Java examples for 2D Graphics:Line

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Description

calculate the the angle of lines

Demo Code


//package com.java2s;

import java.awt.*;

public class Main {
    /**//from   ww w. j a va  2  s  . co m
     * 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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