Origin not in center of Aruco marker

C++
7

Hi,
Thanks for everything!

I use the following version of OpenCV : OpenCV 4.5.5

I tried to draw the axes manually and the result is the same in Gazebo simulation and even in real world with a webcam.

image

Here is the code:

    float mtx[3][3] = {
    {229.41206666, 0.00000000e+00, 292.21276158/2 } ,
    {0.00000000e+00, 229.41206666, 163.36008624} ,
    {0.00000000e+00, 0.00000000e+00, 1.00000000e+00}
    };

    float dist[14][1] = {
    {0.15749949} ,
    {0.71279781} ,
    { -0.00673416} ,
    {-0.04085565} ,
    {3.81203065} ,
    {0.12853096} ,
    {0.76355458} ,
    { 3.70903916} ,
    {0.} ,
    {0.} ,
    {0.} ,
    {0.}
  };

    cv::Mat camMatrix = cv::Mat(3, 3, CV_32F, mtx);
    cv::Mat distCoeffs = cv::Mat(14, 1, CV_32F, dist);

    cv::Ptr<cv::aruco::Dictionary> dictionary = cv::aruco::getPredefinedDictionary(cv::aruco::DICT_6X6_250);

while(video_stream.grab())
              {
                cv::Mat image, imageCopy;
                video_stream.retrieve(image);
                image.copyTo(imageCopy);
                std::vector<std::vector<cv::Point2f>> mycorners,rejected;
                std::vector<cv::Vec3d>rvecs, tvecs;
                std::vector<int> myids;
                cv::aruco::detectMarkers(image, dictionary, mycorners, myids, detectorParams, rejected);

                if (myids.size() > 0)
                {
                  cv::aruco::estimatePoseSingleMarkers(mycorners, MARKER_LENGTH, camMatrix, distCoeffs, rvecs, tvecs);
                  cv::aruco::drawDetectedMarkers(imageCopy, mycorners, myids);

                  vector< cv::Point3f > axisPoints;
                  axisPoints.push_back(cv::Point3f(0, 0, 0));
                  axisPoints.push_back(cv::Point3f(MARKER_LENGTH, 0, 0));
                  axisPoints.push_back(cv::Point3f(0, MARKER_LENGTH, 0));
                  axisPoints.push_back(cv::Point3f(0, 0, MARKER_LENGTH));
                  vector< cv::Point2f > imagePoints;
                  cv::projectPoints(axisPoints, rvecs, tvecs, camMatrix, distCoeffs, imagePoints);
                  cv::line(imageCopy, imagePoints[0], imagePoints[1], cv::Scalar(0, 0, 255), 3);
                  cv::line(imageCopy, imagePoints[0], imagePoints[2], cv::Scalar(0, 255, 0), 3);
                  cv::line(imageCopy, imagePoints[0], imagePoints[3], cv::Scalar(255, 0, 0), 3);
                }

                  imshow("receiver", imageCopy);
                  char key = (char) cv::waitKey(10);
                  if (key == 27)
                    break;
              }