Convexity defects C++ OpenCv

Question

I would be grateful to you if you could help me with this issue :)

Relating to this question cvConvexityDefects in OpenCV 2.X / C++?, I have the same problem. The Op

Answer 1

found some direct approach using the cpp convexityDefects. Typehandling by convexHull-function. It fills by type, int* returns indizes, Point* returns coordinates.

void WorkFrame( Mat img, double minArea )
{
//assumption:
// img already preprocessed, threshold, gray, smooth, morphology whatever..

//get some contours
vector > contours;
vector hierarchy;
findContours( img, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE );

for( int i=0; i& c=contours[i];
    double area = contourArea( c );
        if( area ptHull1; //uncomment and compare to ptHull2
    //convexHull( c, ptHull1 ); //convexHull is smart and fills direct coordinates

    std::vector ihull; 
    convexHull( c, ihull ); //convexHull is smart and fills in contourIndices

    std::vector defects;
    convexityDefects( c, ihull, defects ); //expects indexed hull (internal assertion mat.channels()==1)

    std::vector< Point > ptHull2;
    std::vector::iterator ii=ihull.begin();
    while( ii!=ihull.end() )
    {
        int idx=(*ii);
        ptHull2.push_back( c[idx] );
        ii++;
    }
    cv::polylines( mat, c, true, Scalar( 0xCC,0xCC,0xCC ), 1 );
    cv::polylines( mat, ptHull2, true, Scalar( 0xFF, 0x20, 0x20 ), 1 );

    std::vector::iterator d=defects.begin();
    while( d!=defects.end() )
    {
        Vec4i& v=(*d); d++;
        int startidx=v[0]; Point ptStart( c[startidx] );
        int endidx=v[1]; Point ptEnd( c[endidx] );
        int faridx=v[2]; Point ptFar( c[faridx] );

        cv::circle( img, ptStart, 4, Scalar( 0x02,0x60,0xFF ), 2 );
        cv::circle( img, ptEnd,   4, Scalar( 0xFF,0x60,0x02 ), 2 );
        cv::circle( img, ptFar,   4, Scalar( 0x60,0xFF,0x02 ), 2 );
    }
}

}