OpenCV:凸包

当评价一个点集的2D空间分布时，凸包是一个有用的工具。这个点集可以是轮廓、关键点集合等。

计算凸包，OpenCV提供了函数：

convexHull(Mat(points), hull, true);

下面的OpenCV示例程序，随机产生了一个点集，然后计算了它的凸包。并将点集和凸包画了出来。

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include 
#include 

using namespace cv;
using namespace std;

static void help()
{
    cout << "\nThis sample program demonstrates the use of the convexHull() function\n"
        << "Call:\n"
        << "./convexhull\n" << endl;
}

int main(int /*argc*/, char** /*argv*/)
{
    Mat img(500, 500, CV_8UC3);
    RNG& rng = theRNG();

    help();

    for (;;)
    {
        img = Scalar::all(0);
        Mat img_filled = img.clone();

        char key;
        int i, count = (unsigned)rng % 100 + 1;

        vector points;

        for (i = 0; i < count; i++)
        {
            Point pt;
            pt.x = rng.uniform(img.cols / 4, img.cols * 3 / 4);
            pt.y = rng.uniform(img.rows / 4, img.rows * 3 / 4);

            points.push_back(pt);
        }

        for (i = 0; i < count; i++)
            circle(img, points[i], 3, Scalar(0, 0, 255), CV_FILLED, CV_AA);

        //求凸包
        vector<int> hull;
        convexHull(Mat(points), hull, true);

        //凸包顶点集
        int hullcount = (int)hull.size();
        vector vertices;
        for (int i = 0; i < hullcount;i++)
        {
            vertices.push_back(points[hull[i]]);
        }

        //画线
        Point pt0 = points[hull[hullcount - 1]];
        for (i = 0; i < hullcount; i++)
        {
            Point pt = vertices[i];
            line(img, pt0, pt, Scalar(0, 255, 0), 1, CV_AA);
            pt0 = pt;
        }
        imshow("hull", img);

        //填充
        fillConvexPoly(img_filled,  &vertices[0], hullcount, Scalar(255, 0, 255) , 8);
        imshow("hull_filled",img_filled);

        key = (char)waitKey();
        if (key == 27 || key == 'q' || key == 'Q') // 'ESC'
            break;
    }

    return 0;
}