点在多边形内的算法

算法：过点向左作射线，射线与多边形相交的点的个数为奇数，则点在多边形内，否则点不在多边形内。（如下图）

代码：

   public static boolean pointInPoly(Point p,Point[] pointArr){  //判断点是否在多边形内
	double py=p.getY();
	double px=p.getX();                                  //Point是自定义的class
	int numOfCross=0;
	for(int i=0;i<pointArr.length;i++)
	{
		System.out.println("new"+i+":"+pointArr[i].getX()+" "+pointArr[i].getY());
	}
	for(int i=0;i<pointArr.length;i++){
		double p1y=pointArr[i].getY();
		double p2y=pointArr[(i+1)%pointArr.length].getY();
		double p1x=pointArr[i].getX();
		double p2x=pointArr[(i+1)%pointArr.length].getX();
		if(p1y==p2y) continue;
		if(py<Math.min(p1y,p2y)) continue;
		if(py>Math.max(p1y,p2y)) continue;
		double x = (double)(py - p1y) * (double)(p2x - p1x) / (double)(p2y - p1y) + p1x;
		if(x==px) return true;
		if(x>px) numOfCross++;
	}
	if(numOfCross%2==1) return true;
	else return false;
   }

   //点类
   public class Point {
private double x;
private double y;

public Point() {
    }
    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;
}


 }