三、地图、java实现判断点是否在多边形内
一、有些时候,地图的业务需要判断一个点的经纬度坐标是否落在多边形内
这是我找到的算法的java实现,误差在1米内,可直接使用
代码如下:
/** * 判断点是否在多边形内,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 * @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(); //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 boolean boundOrVertex = true; //cross points count of x int intersectCount = 0; //浮点类型计算时候与0比较时候的容差 double precision = 2e-10; //neighbour bound vertices Point2D.Double p1, p2; 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)){ //p is an vertex return boundOrVertex; } 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 } if(intersectCount % 2 == 0){ //偶数在多边形外 return false; } else { //奇数在多边形内 return true; } }