Returns the area^2 of the triangle formed by three points (x1, y1), (x2, y2) and (x3, y3).

Description

Demo Code

/*//from   ww w.ja va2s .  c  o m
 * Copyright (c) JenSoft API
 * This source file is part of JenSoft API, All rights reserved.
 * JENSOFT PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
//package com.java2s;

public class Main {
    /**
     * Returns the area^2 of the triangle formed by three points (x1, y1), (x2,
     * y2) and (x3, y3).
     */
    public static double getTriangleAreaSq(double x1, double y1, double x2,
            double y2, double x3, double y3) {
        double ax = x1 - x2;
        double ay = y1 - y2;

        double bx = x2 - x3;
        double by = y2 - y3;

        double cx = x3 - x1;
        double cy = y3 - y1;

        double a = (ax * ax + ay * ay) / 2;
        double b = (bx * bx + by * by) / 2;
        double c = (cx * cx + cy * cy) / 2;

        // the following two if statements increase the numerical stability in
        // the
        // case of "needle" triangles. 'a' is made to be the smallest number.

        if (b < a) {
            double t = a;
            a = b;
            b = t;
        }

        if (c < a) {
            double t = a;
            a = c;
            c = t;
        }

        double d = (a + (b - c)) / 2;
        return a * b - d * d;
    }

    /**
     * Returns the area^2 of the triangle formed by the 3 side-lengths 'a', 'b'
     * and 'c'.
     * 
     * @throws IllegalArgumentException
     *             if the side-lengths are less than 0 or cannot form a
     *             triangle.
     */
    public static double getTriangleAreaSq(double a, double b, double c) {
        // implementation based on notes from:
        // http://http.cs.berkeley.edu/~wkahan/Triangle.pdf
        // 1. constraint checking is done
        // 2. numbers are sorted such that a >= b >= c
        // 3. stable equation is used to compute the area

        if (a < 0) {
            throw new IllegalArgumentException("a >= 0 required");
        }
        if (b < 0) {
            throw new IllegalArgumentException("b >= 0 required");
        }
        if (c < 0) {
            throw new IllegalArgumentException("c >= 0 required");
        }

        if (a > b + c) {
            throw new IllegalArgumentException("a <= b + c required");
        }
        if (b > a + c) {
            throw new IllegalArgumentException("b <= a + c required");
        }
        if (c > a + b) {
            throw new IllegalArgumentException("c <= a + b required");
        }

        if (a < c) {
            double t = c;
            c = a;
            a = t;
        }

        if (b < c) {
            double t = c;
            c = b;
            b = t;
        }

        if (a < b) {
            double t = b;
            b = a;
            a = t;
        }

        return (a + (b + c)) * (c - (a - b)) * (c + (a - b))
                * (a + (b - c)) / 16.0;
    }
}

Returns the area^2 of the triangle formed by three points (x1, y1), (x2, y2) and (x3, y3). - Java java.lang

Description

Demo Code

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