判斷點與不規則多邊形的位置關係

判斷點與不規則多邊形的位置關係可以有多種方式，這裏採用射線法結合邊界條件判斷

原理參照https://wenku.baidu.com/view/5e3913a2b0717fd5360cdccf.html

實體類

public class Point{

    /**
     * x軸座標
     */
    double x;
    /**
     * y軸座標
     */
    double y;

    public Point setPoint(Point point){
        this.x = point.getX();
        this.y = point.getY();
        return this;
    }

    public Point() {
    }

    public Point(Float[] point){
        this.x = point[0];
        this.y = point[1];
    }

    public Point(Double[] point) {
        this.x = point[0];
        this.y = point[1];
    }

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public double getX() {
        return x;
    }

    public void setX(double x) {
        this.x = x;
    }

    public double getY() {
        return y;
    }

    public void setY(double y) {
        this.y = y;
    }


}

工具類

import java.util.ArrayList;
import java.util.List;

public class GeometryUtil {


	/**
	 * 判斷點是否在多邊形內
	 * 
	 * @param point
	 *            檢測點
	 * @param pts
	 *            多邊形的頂點
	 * @return 點在多邊形內返回true,否則返回false
	 */
	public static boolean IsPointInPolygon(Point point, List<Point> pts) {

		int N = pts.size();
		boolean boundOrVertex = true; // 邊際條件判斷，如果點位於多邊形的頂點或邊上，也算做點在多邊形內，直接返回true
		int intersectCount = 0;// cross points count of x
		double precision = 2e-10; // 浮點類型計算時候與0比較時候的容差
		Point p1, p2;// neighbour bound vertices
		Point p = point; // 當前點

		p1 = pts.get(0);// left vertex
		for (int i = 1; i <= N; ++i) {// check all rays
			if (p.equals(p1)) {
				return boundOrVertex;// p is an vertex
			}

			p2 = pts.get(i % N);// right vertex
			if (p.x < Math.min(p1.x, p2.x) || p.x > Math.max(p1.x, p2.x)) {
				p1 = p2;
				continue;// next ray left point
			}

			if (p.x > Math.min(p1.x, p2.x) && p.x < Math.max(p1.x, p2.x)) {
				if (p.y <= Math.max(p1.y, p2.y)) {// x is before of ray
					if (p1.x == p2.x && p.y >= Math.min(p1.y, p2.y)) {
						return boundOrVertex;
					}

					if (p1.y == p2.y) {
						if (p1.y == p.y) {
							return boundOrVertex;
						} else {// before ray
							++intersectCount;
						}
					} else {// cross point on the left side
						double xinters = (p.x - p1.x) * (p2.y - p1.y)
								/ (p2.x - p1.x) + p1.y;// cross point of y
						if (Math.abs(p.y - xinters) < precision) {
							return boundOrVertex;
						}

						if (p.y < xinters) {// before ray
							++intersectCount;
						}
					}
				}
			} else {
				if (p.x == p2.x && p.y <= p2.y) {// p crossing over p2
					Point p3 = pts.get((i + 1) % N); // next vertex
					if (p.x >= Math.min(p1.x, p3.x)
							&& p.x <= Math.max(p1.x, p3.x)) {
						++intersectCount;
					} else {
						intersectCount += 2;
					}
				}
			}
			p1 = p2;// next ray left point
		}

       //交點數爲偶數即在內部，否則是外部
		return intersectCount % 2 == 0;

	}



}