OpenCV 3 中的 PCA 错误

Posted 2023-02-22

【中文标题】OpenCV 3 中的 PCA 错误

【英文标题】：Error with PCA in OpenCV 3

【发布时间】：2016-05-23 14:41:31

【问题描述】：

我正在尝试从此链接运行来自 OpenCV for PCA 的示例代码 PCA example.

但是在我运行之后它就崩溃了。我进行了调试，发现它在for loop 下方发生故障，它位于getOrientation 函数中：

    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));
    eigen_val[i] = pca_analysis.eigenvalues.at<double>(0, i);

我之前在***中搜索过，有类似标题但错误不同的问题。有什么帮助吗？谢谢

这里是示例代码：

#include <iostream>
#include <opencv2/opencv.hpp>
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));
        eigen_val[i] = pca_analysis.eigenvalues.at<double>(0, i);
    *
    // 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]));
    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]));
    drawAxis(img, cntr, p1, Scalar(0, 255, 0), 1);
    drawAxis(img, cntr, p2, Scalar(255, 255, 0), 5);
    double angle = atan2(eigen_vecs[0].y, eigen_vecs[0].x); // orientation in radians
    return angle;

int main(int, char** argv)

    // Load image
    Mat src = imread("C:/Users/aydin/Desktop/c++/pictures/pca_test1.jpg");
    //Mat src = imread(argv[1]);
    // Check if image is loaded successfully
    if (!src.data || src.empty())
    
        cout << "Problem loading image!!!" << endl;
        return EXIT_FAILURE;
    
    imshow("src", src);
    // Convert image to grayscale
    Mat gray;
    cvtColor(src, gray, COLOR_BGR2GRAY);
    // Convert image to binary
    Mat bw;
    threshold(gray, bw, 50, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);
    // 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(src, contours, static_cast<int>(i), Scalar(0, 0, 255), 2, 8, hierarchy, 0);
        // Find the orientation of each shape
        //getOrientation(contours[i], src);
    
    imshow("output", src);
    waitKey(0);
    return 0;

【问题讨论】：

我尝试运行示例中的代码，它的输出符合预期。你的编译器和其他环境是什么？

我在 windows 10 上使用 opencv 3 和 visual studio 2015 。当我评论“getOrientation”功能时，它可以正常工作并显示带有计数器但没有方向的图像

尝试重新启动）我认为，问题出在您的环境中。此代码按预期工作。没有足够的信息可以帮助您。

【参考方案1】：

不，这与环境无关；我不知道，你是如何让它工作的，但后来我看到了同样的错误here，他输入了正确的代码，说它有错误。但是将此代码与原始代码进行比较我在“for循环”中看到了一个我提到的问题

   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));

        eigen_val[i] = pca_analysis.eigenvalues.at<double>(0,i);
    

，他将最后一个括号从 (0,i) 更改为 (i) 。我也是这样做的，但我不明白为什么，你能告诉我为什么吗？