c++ - How can I find the largest quadrangle -


how can find largest quadrangle in case?

in attached image can see have (in left) , wantto (in rigth). enter image description here

this code won't work because largest rectangle has crosses instead of corners.

int gamecontroller::getindexofexternalcontour(vector<vector<point>> contours) {     int largest_area=0; int largest_contour_index=0;  for( int = 0; i< contours.size(); i++ )           // iterate through each contour.  {     double = contourarea(contours[i], false);     //  find area of contour     if(a > largest_area)     {         largest_area = a;         largest_contour_index = i;                  //store index of largest contour     } }

i wanted add convexity defects approach.

find largest contour, defect points, connect extremes.

// stl #include <algorithm> #include <iterator> #include <limits> using namespace std;  // cv #include <opencv2/opencv.hpp> using namespace cv;  int main() {     mat sample = imread("path/to/sample.jpg");     imshow("window", sample);     waitkey(0);      // images work on     mat black = mat(sample.rows, sample.cols, cv_8uc1, scalar(0));     mat clone = sample.clone();      // binarization     mat gray;     cvtcolor(sample, gray, cv_bgr2gray);     threshold(gray, gray, 127, 255, cv_thresh_otsu);      // find , fill largest contour     vector<vector<point> > contours;     vector<double> areas;     findcontours(gray, contours, cv_retr_list, cv_chain_approx_simple);     for(unsigned int = 0; < contours.size(); i++)     {         areas.push_back(abs(contourarea(contours[i])));     }     vector<double>::iterator biggest = max_element(areas.begin(), areas.end());     unsigned int id = distance(areas.begin(), biggest);     drawcontours(black, contours, id, scalar(255), -1);     imshow("window", black);     waitkey(0);      // convexity defects of thelargest contour     vector<point> external = contours[id];     vector<int> hull;     vector<vec4i> defects;     convexhull(external, hull);     convexitydefects(external, hull, defects);      // show defect points     for(unsigned int = 0; < defects.size(); i++)     {         circle(clone, external[defects[i][1]], 1, scalar(0, 255, 255), 3);     }     imshow("window", clone);     waitkey(0);      // find extremes     point tl, tr, bl, br;     point p;     double d_tl, d_tr, d_bl, d_br;     double m_tl = numeric_limits<double>::max();     double m_tr = numeric_limits<double>::max();     double m_bl = numeric_limits<double>::max();     double m_br = numeric_limits<double>::max();     for(unsigned int = 0; < defects.size(); i++)     {         p = external[defects[i][2]];         d_tl = (double)sqrt((double)pow((double)(p.x),2) + pow((double)(p.y),2));         d_tr = (double)sqrt((double)pow((double)(sample.cols - p.x),2) + pow((double)(p.y),2));         d_bl = (double)sqrt((double)pow((double)(p.x),2) + pow((double)(sample.rows - p.y),2));         d_br = (double)sqrt((double)pow((double)(sample.cols - p.x),2) + pow((double)(sample.rows - p.y),2));         if(d_tl < m_tl)         {             tl = p;             m_tl = d_tl;         }         if(d_tr < m_tr)         {             tr = p;             m_tr = d_tr;         }         if(d_bl < m_bl)         {             bl = p;             m_bl = d_bl;         }         if(d_br < m_br)         {             br = p;             m_br = d_br;         }     }      // draw rectangle     line(sample, tl, tr, scalar(0, 255, 255), 3);     line(sample, tr, br, scalar(0, 255, 255), 3);     line(sample, br, bl, scalar(0, 255, 255), 3);     line(sample, bl, tl, scalar(0, 255, 255), 3);     imshow("window", sample);     waitkey(0);      return 0; }

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you need try approach last step (find extreme defects)


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