Java判断点是否在多边形内
背景
服务器端根据某个点获取是否在多边形内的算法一直有需求,比如判断某经纬度点是否在一个多边形内。但是算法结果并不是特别精确。
暂使用该方法,后期有优化再编辑
代码
import java.awt.geom.Point2D;
import java.util.ArrayList;
import java.util.List;
public class MapUtil {
/**
* 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.Double point, List<Point2D.Double> 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.Double p1, p2;//neighbour bound vertices
Point2D.Double 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.Double 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
}
return intersectCount % 2 != 0;
}
public static void main(String[] args) {
//监测点
Point2D.Double point = new Point2D.Double(Double.valueOf(120.2045510000), Double.valueOf(35.9663840000));
//多边形顶点
List<Point2D.Double> list = new ArrayList<>();
list.add(point);
boolean rst = isPtInPoly(point, list);
}
}
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