c++ - 如何在opencv的Aruco标记上绘制矩形？

Question

我有一个程序可以绘制和检测aruco标记，并在上面写标记id。我需要一个矩形而不是标记id出现在每个标记上，我可以绘制一个矩形，但固定位置不在标记上，这是代码:

#include <opencv2\highgui.hpp>
#include <opencv2\aruco.hpp>
#include <opencv2\core.hpp>
#include <opencv2\imgcodecs.hpp>
#include <opencv2\imgproc.hpp>
#include <opencv2\calib3d.hpp>
#include <sstream>
#include <fstream>
#include <iostream>
using namespace cv;
using namespace std;


int main(int argc, char *argv[]) {
    cv::VideoCapture inputVideo;
    inputVideo.open(0);
    Mat outputMarker;
    auto  markerDict = aruco::getPredefinedDictionary(aruco::PREDEFINED_DICTIONARY_NAME::DICT_4X4_50);
    for (int i = 0; i < 50; i++) {
        aruco::drawMarker(markerDict, i, 500, outputMarker, 1);
        ostringstream convert;
        String imageName = "4x4marker_";
        convert << imageName << i << ".jpg";
        imwrite(convert.str(), outputMarker);

        while (inputVideo.grab()) {
            cv::Mat image, imageCopy;
            inputVideo.retrieve(image);
            image.copyTo(imageCopy);

            std::vector<int> ids;
            std::vector<std::vector<cv::Point2f> > corners;
            cv::aruco::detectMarkers(image, markerDict, corners, ids);

            // if at least one marker detected
            if (ids.size() > 0)
                cv::aruco::drawDetectedMarkers(imageCopy, corners, ids);
            int x = 0;
            int y = 3;


            rectangle(imageCopy, Point(imageCopy.cols/2, imageCopy.rows/2),
                Point(x,y),Scalar::all(255), -1, 8, 0);



            cv::imshow("out", imageCopy);
            char key = (char)cv::waitKey(5);
            if (key == 27)
                break;
        }
    }
}

用于简化代码测试的示例标记。

Answer 1

使用 detectMarkers 函数时，它将返回每次检测的角点。您的情况是将其放入std::vector<std::vector<cv::Point2f> > corners中。要绘制所需的矩形，您可以执行类似的操作(，以下代码为示例，尚未经过的测试):

for (size_t i = 0; i< corners.size(); +i)
{
  cv::Point2f p0(image.cols,image.rows);
  cv::Ponit2f p1(0,0);
  for (auto p: corners[i])
  {
    if (p.x < p0.x)
      p0.x = p.x;
    if (p.y < p0.y)
      p0.y = p.y;
    if (p.x > p1.x)
      p1.x = p.x;
    if (p.y > p1.y)
      p1.y = p.y;
  }
  rectangle(imageCopy, p0, p1,Scalar::all(255), -1, 8, 0);
}

但是，您可能希望绘制一个更适合标记的多边形，因为如果标记不完全垂直于相机光轴并且没有扭曲，则图像上的标记投影将不是矩形。为此，您可以使用 fillPoly ，或者如果您不希望它填充 line 。

Here是一个功能完整的示例，已在OpenCV 4.3.0-pre和3.2.0(在Ubuntu中)和3.4.9(在Windows中)进行了测试:

#include <iostream>

#include <opencv2/aruco.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>

int main(int argc, char** argv)
{
  // Check cv versionmake
  std::cout << "Using OpenCV version: " << CV_VERSION << std::endl;

  // Create video input
  cv::VideoCapture inputVideo;
  int input_source(0);
  if (argc > 1)
    input_source = std::atoi(argv[1]);
  if (!inputVideo.open(input_source))
  {
    std::cerr << "Error opening input video soruce: " << input_source << std::endl;
    return EXIT_FAILURE;
  }

  // Create marker dictionary
  auto marker_dict = cv::aruco::getPredefinedDictionary(cv::aruco::PREDEFINED_DICTIONARY_NAME::DICT_4X4_50);

  // Get imshow ready
  cv::namedWindow("Display window", cv::WINDOW_KEEPRATIO | cv::WINDOW_NORMAL);
  cv::resizeWindow("Display window", 800, 600);

  // Grab images until escape is pressed
  int key = 0;
  while (key != 27 && inputVideo.grab())
  {
    // Retrieve image
    cv::Mat image;
    inputVideo.retrieve(image);

    // Get image output ready
    cv::Size image_size = image.size();
    cv::Mat out_image(image_size.height, 3 * image_size.width, CV_8UC3);
    cv::Mat left(out_image, cv::Rect(0, 0, image_size.width, image_size.height));
    image.copyTo(left);
    cv::Mat mid(out_image, cv::Rect(image_size.width, 0, image_size.width, image_size.height));
    image.copyTo(mid);
    cv::Mat right(out_image, cv::Rect(2 * image_size.width, 0, image_size.width, image_size.height));
    image.copyTo(right);

    // Add names to images
    int corner_offset = 50;
    cv::putText(left, "Original image", cv::Point(corner_offset, corner_offset), cv::FONT_HERSHEY_DUPLEX, 1.0,
                CV_RGB(0, 0, 0), 2);
    cv::putText(mid, "Image with OpenCV drawing", cv::Point(corner_offset, corner_offset), cv::FONT_HERSHEY_DUPLEX, 1.0,
                CV_RGB(0, 0, 0), 2);
    cv::putText(right, "Image with custom drawing", cv::Point(corner_offset, corner_offset), cv::FONT_HERSHEY_DUPLEX,
                1.0, CV_RGB(0, 0, 0), 2);

    // Detect markers
    std::vector<int> ids;
    std::vector<std::vector<cv::Point2f> > corners;
    cv::aruco::detectMarkers(image, marker_dict, corners, ids);

    // Draw markers using opencv tool
    cv::aruco::drawDetectedMarkers(mid, corners, ids);

    // Draw markers custom
    for (size_t i = 0; i < corners.size(); ++i)
    {
      // Convert to integer ponits
      int num = static_cast<int>(corners[i].size());
      std::vector<cv::Point> points;
      for (size_t j = 0; j < corners[i].size(); ++j)
        points.push_back(cv::Point(static_cast<int>(corners[i][j].x), static_cast<int>(corners[i][j].y)));
      const cv::Point* pts = &(points[0]);

      // Draw
      cv::fillPoly(right, &pts, &num, 1, cv::Scalar(255, 0, 0));

      // Draw contour
      for (size_t j = 0; j < corners[i].size(); ++j)
      {
        size_t next = (j + 1) % corners[i].size();
        cv::line(right, corners[i][j], corners[i][next], cv::Scalar(0, 255, 0), 5);
      }
    }

    // Display
    cv::imshow("Display window", out_image);
    key = cv::waitKey(5);
  }

  return EXIT_SUCCESS;
}

这是您将通过以下代码获得的输出: