GIS算法总结——判断一个点的经纬度是否在多边形面内(js代码)

分类:计算机 | GIS | 综合 99
更新:2022-06-24 16:48:30
编辑

转载地址

https://blog.csdn.net/qilin001cs/article/details/106783374

var isPointInPolygon = function(point,pts){
    var N = pts.length;  //pts [{lat:xxx,lng:xxx},{lat:xxx,lng:xxx}]
    var 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
    var intersectCount = 0;//cross points count of x
    var precision = 2e-10; //浮点类型计算时候与0比较时候的容差
    var p1, p2;//neighbour bound vertices
    var p = point; //point {lat:xxx,lng:xxx}

    p1 = pts[0];//left vertex
    for(var i = 1; i <= N; ++i){//check all rays
        if((p.lat==p1.lat)&&(p.lng==p1.lng)){
           return boundOrVertex;//p is an vertex
        }
        p2 = pts[i % N];//right vertex
        if(p.lat < Math.min(p1.lat, p2.lat) || p.lat > Math.max(p1.lat, p2.lat)){//ray is outside of our interests
           p1 = p2;
           continue;//next ray left point
        }
        if(p.lat > Math.min(p1.lat, p2.lat) && p.lat < Math.max(p1.lat, p2.lat)){//ray is crossing over by the algorithm (common part of)
            if(p.lng <= Math.max(p1.lng, p2.lng)){//x is before of ray
               if(p1.lat == p2.lat && p.lng >= Math.min(p1.lng, p2.lng)){//overlies on a horizontal ray
                    return boundOrVertex;
               }
               if(p1.lng == p2.lng){//ray is vertical
                  if(p1.lng == p.lng){//overlies on a vertical ray
                       return boundOrVertex;
                   }else{//before ray
                      ++intersectCount;
                   }
               }else{//cross point on the left side
                    var xinters = (p.lat - p1.lat) * (p2.lng - p1.lng) / (p2.lat - p1.lat) + p1.lng;//cross point of lng
                    if(Math.abs(p.lng - xinters) < precision){//overlies on a ray
                        return boundOrVertex;
                    }
                    if(p.lng < xinters){//before ray
                       ++intersectCount;
                    }
               }
            }
        }else{//special case when ray is crossing through the vertex
            if(p.lat == p2.lat && p.lng <= p2.lng){//p crossing over p2
                var p3 = pts[(i+1) % N]; //next vertex
                if(p.lat >= Math.min(p1.lat, p3.lat) && p.lat <= Math.max(p1.lat, p3.lat)){//p.lat lies between p1.lat & p3.lat
                    ++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;
    }
};