[算法]Python判断一个点是否在多边形内部

题目：

 

代码：

# -*- coding:utf-8 -*-

def rayCasting(p, poly):
    px = p['x']
    py = p['y']
    flag = False

    i = 0
    l = len(poly)
    j = l - 1
    #for(i = 0, l = poly.length, j = l - 1; i < l; j = i, i++):
    while i < l:
        sx = poly[i]['x']
        sy = poly[i]['y']
        tx = poly[j]['x']
        ty = poly[j]['y']

        #点与多边形顶点重合
        if (sx == px and sy == py) or (tx == px and ty == py):
            return (px, py)

        #判断线段两端点是否在射线两侧
        if (sy < py and ty >= py) or (sy >= py and ty < py):
            #线段上与射线 Y 坐标相同的点的 X 坐标
            x = sx + (py - sy) * (tx - sx) / (ty - sy)
            #点在多边形的边上
            if x == px:
                return (px,py)
            #射线穿过多边形的边界
            if x > px:
                flag = not flag
        j = i
        i += 1

    #射线穿过多边形边界的次数为奇数时点在多边形内
    return (px,py) if flag else 'out'

#根据数组下标奇偶数得到点的坐标
def getpoint(a):
    i = 0
    zhima = []
    while i < len(a.split(',')[1::2]):
        zhima.append({'x': float(a.split(',')[::2][i]),'y': float(a.split(',')[1::2][i])})
        i += 1
    return zhima

#根据输入的点循环判断芝麻是否在多边形里面，如果全部在外面则输出no,否则输出芝麻的坐标
def rs(zhima, duobianxing):
    zm = getpoint(zhima)
    dbx = getpoint(duobianxing)
    count = 0
    for point in zm:
        rs = rayCasting(point, dbx)
        if rs == 'out':
            count += 1
        else:
            print rs
    if count == len(zm):
        print "no"


zhima = "6,4,8,8,9,9"
duobianxing = "1,1,7,3,5,7"
rs(zhima,duobianxing)

　　

结果：