####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
//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/