判断点是否在不规则矩形区域opencv demo

Point in Polygon 问题 opencv3.2 demo

一、Background

　　最近做相关项目检测某一点是否在划定的一个区域内，百度之后发现了这类问题属于Point in Polygon。主要有两种方法解决：

1、Crossing Number (cn) 方法
　　测试点作为起点画一条射线穿过不规则区域，与区域相交的点为奇数则此点在区域内，为偶数则在区域外，此种情况不准确（射线穿过不规则矩形框顶点时）。
　　

2、Winding Number (wn)方法
　　这种方法是一种环绕算法，可参考这里。
　　

二、DEMO

　　用opencv实现了一个demo（由于某些原因使用的opencv c接口），即手动点不规则矩形的点，自动画线生成不规则矩形框。之后可在图片任意区域内鼠标左键点点，如果点在区域内，则显示为红点；若不在区域内则显示为蓝点。如图下图所示。代码主要参考了http://geomalgorithms.com/a03-_inclusion.html；

三、CODE

#include "opencv2\highgui\highgui_c.h"#include "opencv2\imgproc\imgproc_c.h"#include "opencv2\core\core_c.h"#include "opencv2\imgcodecs\imgcodecs_c.h"#include "opencv2\core\types_c.h"#include <stdio.h>#define POINT_NUM 6//不规则矩形顶点数int wn_PnPoly(CvPoint P, CvPoint* V, int n);CvPoint vertex_point[POINT_NUM],testpoint;IplImage *org;void on_mouse(int EVENT, int x, int y, int flags, void* userdata){    static int i = 0,ii=1;    CvScalar color_b = CV_RGB(0, 0, 255);    CvScalar color_r = CV_RGB(255, 0, 0);    switch (EVENT)    {    case CV_EVENT_LBUTTONDOWN:        if (ii)        {            vertex_point[i] = cvPoint(x, y);            cvCircle(org, vertex_point[i], 1, color_r,2,4,0);            printf("vertex_point[%d]->(%d,%d)\n", i, vertex_point[i].x, vertex_point[i].y);            if (i >= 1)            {                cvLine(org, vertex_point[i - 1], vertex_point[i], color_r, 3, 4, 0);                if (i == POINT_NUM - 1)                {                    cvLine(org, vertex_point[i], vertex_point[0], color_r, 3, 4, 0);                    vertex_point[POINT_NUM] = vertex_point[0];                    ii = 0;                }            }            i++;        }        else        {                   testpoint=cvPoint(x, y);                int out_in=wn_PnPoly(testpoint, vertex_point, POINT_NUM);            if (out_in==0)//outside            {                cvCircle(org, testpoint, 2, color_b, 2, 4, 0);                  printf("outside!\n");            }            else//inside            {                cvCircle(org, testpoint, 2, color_r, 2, 4, 0);                printf("inside!\n");            }        //  printf("result:%d", out_in);            }        break;    default:        break;    }}inline int isLeft(CvPoint P0, CvPoint P1, CvPoint P2){    return ((P1.x - P0.x) * (P2.y - P0.y)        - (P2.x - P0.x) * (P1.y - P0.y));}int cn_PnPoly(CvPoint P, CvPoint* V, int n){    int    cn = 0;    // the  crossing number counter                      // loop through all edges of the polygon    for (int i = 0; i<n; i++) {    // edge from V[i]  to V[i+1]        if (((V[i].y <= P.y) && (V[i + 1].y > P.y))     // an upward crossing            || ((V[i].y > P.y) && (V[i + 1].y <= P.y))) { // a downward crossing                                                          // compute  the actual edge-ray intersect x-coordinate            float vt = (float)(P.y - V[i].y) / (V[i + 1].y - V[i].y);            if (P.x <  V[i].x + vt * (V[i + 1].x - V[i].x)) // P.x < intersect                ++cn;   // a valid crossing of y=P.y right of P.x        }    }    return (cn & 1);    // 0 if even (out), and 1 if  odd (in)}int wn_PnPoly(CvPoint P, CvPoint* V, int n){    int    wn = 0;    // the  winding number counter                      // loop through all edges of the polygon    for (int i = 0; i<n; i++) {   // edge from V[i] to  V[i+1]        if (V[i].y <= P.y) {          // start y <= P.y            if (V[i + 1].y  > P.y)      // an upward crossing                if (isLeft(V[i], V[i + 1], P) > 0)  // P left of  edge                    ++wn;            // have  a valid up intersect        }        else {                        // start y > P.y (no test needed)            if (V[i + 1].y <= P.y)     // a downward crossing                if (isLeft(V[i], V[i + 1], P) < 0)  // P right of  edge                    --wn;            // have  a valid down intersect        }    }    return wn;}int main(){    org = cvLoadImage("lena.jpg", CV_LOAD_IMAGE_COLOR);    cvNamedWindow("lena", CV_WINDOW_AUTOSIZE);    cvSetMouseCallback("lena", on_mouse, 0);    while (true)    {        cvShowImage("lena", org);        if (cvWaitKey(20) ==13)break;    }    cvReleaseImage(&org);    cvDestroyAllWindows();}

四、References

1.https://www.zhihu.com/question/26551754
2.http://geomalgorithms.com/a03-_inclusion.html