通过多点连成折线，显示折线周围20米（可自定义）范围内点位

Question

操作逻辑：通过多点连成折线，显示折线周围20米（可自定义）范围内点位
求虚线内缓冲区范围

Answer 1

是给定折线构成的封闭范围，求点在范围内还是范围外么？

/** 
        * 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;
           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;
           Point2D.Double p = point; //当前点  

           p1 = pts.get(0);   
           for(int i = 1; i <= N; ++i){      
               if(p.equals(p1)){  
                   return boundOrVertex;
               }  
               p2 = pts.get(i % N);        
               if(p.x < Math.min(p1.x, p2.x) || p.x > Math.max(p1.x, p2.x)){                
                   p1 = p2;   
                   continue;
               }  

               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)){                 
                       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{
                               ++intersectCount;  
                           }   
                       }else{
                           double xinters = (p.x - p1.x) * (p2.y - p1.y) / (p2.x - p1.x) + p1.y;                       
                           if(Math.abs(p.y - xinters) < precision){
                               return boundOrVertex;  
                           }  

                           if(p.y < xinters){ 
                               ++intersectCount;  
                           }   
                       }  
                   }  
               }else{                 
                   if(p.x == p2.x && p.y <= p2.y){                    
                       Point2D.Double p3 = pts.get((i+1) % N);                      
                       if(p.x >= Math.min(p1.x, p3.x) && p.x <= Math.max(p1.x, p3.x)){
                           ++intersectCount;  
                       }else{  
                           intersectCount += 2;  
                       }  
                   }  
               }              
               p1 = p2;  
           }  

           if(intersectCount % 2 == 0){
               return false;  
           } else { 
               return true;  
           }  

        }