js判断点是否在平面几何图形内(基于百度地图方法)

####1. 点线面数据格式

• 点: { x: xxx, y: xxx }
• 线: [{ x: xxx, y: xxx }, { x: xxx, y: xxx }]
• 面: [{ x: xxx, y: xxx }, { x: xxx, y: xxx }, { x: xxx, y: xxx }...

2. 方法详解

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//判断点是否在平面中 function isPointInPolygon(point, polygon) {       //下述代码来源：http://paulbourke.net/geometry/insidepoly/，进行了部分修改     //基本思想是利用射线法，计算射线与多边形各边的交点，如果是偶数，则点在多边形外，否则     //在多边形内。还会考虑一些特殊情况，如点在多边形顶点上，点在多边形边上等特殊情况。       var N = polygon.length;     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; //测试点       p1 = polygon[0]; //left vertex            for (var i = 1; i <= N; ++i) { //check all rays                    if (p.x == p1.x && p.y == p1.y) {             return boundOrVertex; //p is an vertex         }           p2 = polygon[i % N]; //right vertex                    if (p.y < Math.min(p1.y, p2.y) || p.y > Math.max(p1.y, p2.y)) { //ray is outside of our interests                            p1 = p2;             continue; //next ray left point         }           if (p.y > Math.min(p1.y, p2.y) && p.y < Math.max(p1.y, p2.y)) { //ray is crossing over by the algorithm (common part of)             if (p.x <= Math.max(p1.x, p2.x)) { //x is before of ray                                    if (p1.y == p2.y && p.x >= Math.min(p1.x, p2.x)) { //overlies on a horizontal ray                     return boundOrVertex;                 }                   if (p1.x == p2.x) { //ray is vertical                                            if (p1.x == p.x) { //overlies on a vertical ray                         return boundOrVertex;                     } else { //before ray                         ++intersectCount;                     }                 } else { //cross point on the left side                                            var xinters = (p.y - p1.y) * (p2.x - p1.x) / (p2.y - p1.y) + p1.x; //cross point of x                                            if (Math.abs(p.x - xinters) < precision) { //overlies on a ray                         return boundOrVertex;                     }                       if (p.x < xinters) { //before ray                         ++intersectCount;                     }                 }             }         } else { //special case when ray is crossing through the vertex                            if (p.y == p2.y && p.x <= p2.x) { //p crossing over p2                                    var p3 = polygon[(i + 1) % N]; //next vertex                                    if (p.y >= Math.min(p1.y, p3.y) && p.y <= Math.max(p1.y, p3.y)) { //p.y lies between p1.y & p3.y                     ++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;     } }

　　

转载自：https://www.codeleading.com/article/65161367478/