OpenCV 4.x API detailed explanation and C++ example-plane division

Section VII Plane Division

OpencCV provides the Subdiv2D class to calculate Delaunay triangulation or Voronoi diagram.

The following will demonstrate the use of the Subdiv2D class through an example. For Delaunay triangulation and Voronoi diagrams, you can refer to related materials.

#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
#include <iostream>

using namespace cv;
using namespace std;

static void draw_subdiv_point( Mat& img, Point2f fp, Scalar color )
{
    circle( img, fp, 3, color, FILLED, LINE_8, 0 );
}

// 绘制三角形剖分
static void draw_subdiv( Mat& img, Subdiv2D& subdiv, Scalar delaunay_color )
{
    vector<Vec6f> triangleList;
    subdiv.getTriangleList(triangleList);
    vector<Point> pt(3);

    for( size_t i = 0; i < triangleList.size(); i++ )
    {
        Vec6f t = triangleList[i];
        pt[0] = Point(cvRound(t[0]), cvRound(t[1]));
        pt[1] = Point(cvRound(t[2]), cvRound(t[3]));
        pt[2] = Point(cvRound(t[4]), cvRound(t[5]));
        line(img, pt[0], pt[1], delaunay_color, 1, LINE_AA, 0);
        line(img, pt[1], pt[2], delaunay_color, 1, LINE_AA, 0);
        line(img, pt[2], pt[0], delaunay_color, 1, LINE_AA, 0);
    }
}

static void locate_point( Mat& img, Subdiv2D& subdiv, Point2f fp, Scalar active_color )
{
    int e0=0, vertex=0;

    subdiv.locate(fp, e0, vertex);

    if( e0 > 0 )
    {
        int e = e0;
        do
        {
            Point2f org, dst;
            if( subdiv.edgeOrg(e, &org) > 0 && subdiv.edgeDst(e, &dst) > 0 )
                line( img, org, dst, active_color, 3, LINE_AA, 0 );

            e = subdiv.getEdge(e, Subdiv2D::NEXT_AROUND_LEFT);
        }
        while( e != e0 );
    }

    draw_subdiv_point( img, fp, active_color );
}


// 填充
static void paint_voronoi( Mat& img, Subdiv2D& subdiv )
{
    vector<vector<Point2f> > facets;
    vector<Point2f> centers;
    subdiv.getVoronoiFacetList(vector<int>(), facets, centers);

    vector<Point> ifacet;
    vector<vector<Point> > ifacets(1);

    for( size_t i = 0; i < facets.size(); i++ )
    {
        ifacet.resize(facets[i].size());
        for( size_t j = 0; j < facets[i].size(); j++ )
            ifacet[j] = facets[i][j];

        Scalar color;
        color[0] = rand() & 255;
        color[1] = rand() & 255;
        color[2] = rand() & 255;
        fillConvexPoly(img, ifacet, color, 8, 0);

        ifacets[0] = ifacet;
        polylines(img, ifacets, true, Scalar(), 1, LINE_AA, 0);
        circle(img, centers[i], 3, Scalar(), FILLED, LINE_AA, 0);
    }
}


int main( int argc, char** argv )
{

    Scalar active_facet_color(0, 0, 255), delaunay_color(255,255,255);
    Rect rect(0, 0, 600, 600);

    Subdiv2D subdiv(rect);
    Mat img(rect.size(), CV_8UC3);

    img = Scalar::all(0);
    string win = "Delaunay Demo";
    imshow(win, img);

    for( int i = 0; i < 200; i++ )
    {
        Point2f fp( (float)(rand()%(rect.width-10)+5),
                    (float)(rand()%(rect.height-10)+5));

        locate_point( img, subdiv, fp, active_facet_color );
        imshow( win, img );

        if( waitKey( 100 ) >= 0 )
            break;

        subdiv.insert(fp);

        img = Scalar::all(0);
        draw_subdiv( img, subdiv, delaunay_color );
        imshow( win, img );

        if( waitKey( 100 ) >= 0 )
            break;
    }

    img = Scalar::all(0);
    paint_voronoi( img, subdiv );
    imshow( win, img );

    waitKey(0);

    return 0;
}