Ошибка "is block type valid" в момент вывода картинки OpenCV

#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <valarray>
#include <math.h>
 
 
using namespace std;
using namespace cv;
// Function declarations
void drawAxis(Mat&, Point, Point, Scalar, const float);
double getOrientation(const vector<Point> &, Mat&);
void drawAxis(Mat& img, Point p, Point q, Scalar colour, const float scale = 0.2)
{
    double angle;
    double hypotenuse;
    angle = atan2((double)p.y - q.y, (double)p.x - q.x); // angle in radians
    hypotenuse = sqrt((double)(p.y - q.y) * (p.y - q.y) + (p.x - q.x) * (p.x - q.x));
    //    double degrees = angle * 180 / CV_PI; // convert radians to degrees (0-180 range)
    //    cout << "Degrees: " << abs(degrees - 180) << endl; // angle in 0-360 degrees range
    // Here we lengthen the arrow by a factor of scale
    q.x = (int)(p.x - scale * hypotenuse * cos(angle));
    q.y = (int)(p.y - scale * hypotenuse * sin(angle));
    line(img, p, q, colour, 1, CV_AA);
    // create the arrow hooks
    p.x = (int)(q.x + 9 * cos(angle + CV_PI / 4));
    p.y = (int)(q.y + 9 * sin(angle + CV_PI / 4));
    line(img, p, q, colour, 1, CV_AA);
    p.x = (int)(q.x + 9 * cos(angle - CV_PI / 4));
    p.y = (int)(q.y + 9 * sin(angle - CV_PI / 4));
    line(img, p, q, colour, 1, CV_AA);
}
double getOrientation(const vector<Point> &pts, Mat &img)
{
    //Construct a buffer used by the pca analysis
    int sz = static_cast<int>(pts.size());
    Mat data_pts = Mat(sz, 2, CV_64FC1);
    for (int i = 0; i < data_pts.rows; ++i)
    {
        data_pts.at<double>(i, 0) = pts[i].x;
        data_pts.at<double>(i, 1) = pts[i].y;
    }
    //Perform PCA analysis
    PCA pca_analysis(data_pts, Mat(), CV_PCA_DATA_AS_ROW);
    //Store the center of the object
    Point cntr = Point(static_cast<int>(pca_analysis.mean.at<double>(0, 0)),
        static_cast<int>(pca_analysis.mean.at<double>(0, 1)));
    //Store the eigenvalues and eigenvectors
    vector<Point2d> eigen_vecs(2);
    vector<double> eigen_val(2);
    for (int i = 0; i < 2; ++i)
    {
        eigen_vecs[i] = Point2d(pca_analysis.eigenvectors.at<double>(i, 0),
            pca_analysis.eigenvectors.at<double>(i, 1));
        cout << "eigen [" << i << "] = " << eigen_vecs[i];
        eigen_val[i] = pca_analysis.eigenvalues.at<double>(0);  
    }
    // Draw the principal components
    circle(img, cntr, 3, Scalar(255, 0, 255), 2);
    Point p1 = cntr + 0.02 * Point(static_cast<int>(eigen_vecs[0].x * eigen_val[0]), static_cast<int>(eigen_vecs[0].y * eigen_val[0]));
    double angle1 = 180* atan2(eigen_vecs[0].y, eigen_vecs[0].x)/ 3.1416;
    cout << "Angle" << " = " << angle1 << "\n ";
    Point p2 = cntr - 0.02 * Point(static_cast<int>(eigen_vecs[1].x * eigen_val[1]), static_cast<int>(eigen_vecs[1].y * eigen_val[1]));
    double angle2 = 180 * atan2(eigen_vecs[1].y, eigen_vecs[1].x)/3.1416;
    cout << "Angle" << " = " << angle2 << "\n ";
    drawAxis(img, cntr, p1, Scalar(0, 255, 0), 1);
    drawAxis(img, cntr, p2, Scalar(255, 255, 0), 5);
     // orientation in radians  
    return angle1;
}
 
int main(int, char** argv)
{
 
    VideoCapture cap(0); // open the default camera
    if (!cap.isOpened())  // check if we succeeded
        return -1;
 
    Mat edges;
    namedWindow("edges", 1);
    for (;;)
    {
        Mat frame;
        cap >> frame; // get a new frame from camera
        Mat bw;
        Canny(frame, bw, 20, 80);
        // Find all the contours in the thresholded image
        vector<Vec4i> hierarchy;
        vector<vector<Point> > contours;
        findContours(bw, contours, hierarchy, CV_RETR_LIST, CV_CHAIN_APPROX_NONE);
        for (size_t i = 0; i < contours.size(); ++i)
        {
            // Calculate the area of each contour
            double area = contourArea(contours[i]);
            // Ignore contours that are too small or too large
            if (area < 1e2 || 1e5 < area) continue;
            // Draw each contour only for visualisation purposes
            drawContours(frame, contours, static_cast<int>(i), Scalar(0, 0, 255), 2, 8, hierarchy, 0);
            // Find the orientation of each shape
            getOrientation(contours[i], frame);
        }
        imshow("output", frame);
        if (waitKey(30) >= 0) { break; }
    }
    
}