java判断某个点是否在所画范围内(多边形/圆形)

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本文介绍了一种用于判断二维平面上的点是否位于特定多边形或圆形内部的算法。通过计算与多边形边界的交点数量来判断点的位置，并提供了点与圆形位置关系的判断方法。

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测试类

/**
* java判断某个点是否在所画范围内(多边形【isPtInPoly】/圆形【distencePC】)
* @param point 检测点
* @param pts 多边形的顶点
* @return 点在多边形内返回true,否则返回false
* @author        ardo
*/
public class IsPtInPoly {

   /**
   * 判断点是否在多边形内
   * @param point 检测点
   * @param pts 多边形的顶点
   * @return 点在多边形内返回true,否则返回false
   */
   public static boolean isPtInPoly(Point2D point, List<Point2D> pts){

   int N = pts.size();
   boolean boundOrVertex = true; //如果点位于多边形的顶点或边上，也算做点在多边形内，直接返回true
   int intersectCount = 0;//cross points count of x
   double precision = 2e-10; //浮点类型计算时候与0比较时候的容差
   Point2D p1, p2;//neighbour bound vertices
   Point2D p = point; //当前点

   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)){//ray is outside of our interests
   p1 = p2;
   continue;//next ray left point
   }

   if(p.x > Math.min(p1.x, p2.x) && p.x < Math.max(p1.x, p2.x)){//ray is crossing over by the algorithm (common part of)
   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)){//overlies on a horizontal ray
   return boundOrVertex;
   }

   if(p1.y == p2.y){//ray is vertical
   if(p1.y == p.y){//overlies on a vertical ray
   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){//overlies on a ray
   return boundOrVertex;
   }

   if(p.y < xinters){//before ray
   ++intersectCount;
   }
   }
   }
   }else{//special case when ray is crossing through the vertex
   if(p.x == p2.x && p.y <= p2.y){//p crossing over p2
   Point2D 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)){//p.x lies between p1.x & p3.x
   ++intersectCount;
   }else{
   intersectCount += 2;
   }
   }
   }
   p1 = p2;//next ray left point
   }

   if(intersectCount % 2 == 0){//偶数在多边形外
   return false;
   } else { //奇数在多边形内
   return true;
   }

   }

   /**
   * 判断是否在圆形内
   * @param p
   * @param c
   * @return
   */
   public static String distencePC(Point2D p,Circle c){//判断点与圆心之间的距离和圆半径的关系
String s ;
double d2 = Math.hypot( (p.getX() - c.getCC().getX() ), (p.getY() - c.getCC().getY()) );
System.out.println("d2=="+d2);
double r = c.getR();
if(d2 > r){
s = "圆外";
}else if(d2 < r){
s = "圆内";
}else{
s = "圆上";
}
return s;
   }




   public static void main(String[] args) {

   Point2D point = new Point2D(116.404072, 39.916605);

   // 测试一个点是否在多边形内
   List<Point2D> pts = new ArrayList<Point2D>();
   pts.add(new Point2D(116.395, 39.910));
   pts.add(new Point2D(116.394, 39.914));
   pts.add(new Point2D(116.403, 39.920));
   pts.add(new Point2D(116.402, 39.914));
   pts.add(new Point2D(116.410, 39.913));

   if(isPtInPoly(point, pts)){
   System.out.println("点在多边形内");
   }else{
   System.out.println("点在多边形外");
   }

   // 测试一个点是否在圆形内
   Point2D centerPoint = new Point2D(116.404172, 39.916605);
   Circle c = new Circle();
c.setCC(centerPoint);
c.setR(0.0056);
String s = distencePC(point,c);
System.out.println("点是否在圆内："+s);
   }

}

/**
* 圆形类
* @author ardo
*
*/
public class Circle {
private double r;
private Point2D cc;

public void setR(double a){
r = a;
}
public void setCC(Point2D centerOfCir){
cc = centerOfCir;
}
public double getR(){
return r;
}
public Point2D getCC(){
return cc;
}
}

public class Point2D {

   public double x;
   public double y;

   public Point2D(double x, double y) {
       super();
       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;
   }

}