error: ‘ArucoDetector’ is not a member of ‘cv::aruco’

Question

I am building a program in ROS using OpenCV C++ to detect ArUco codes.My OpenCV version is 4.2. I've included the header file: #include <opencv2/aruco.hpp>. And called the function： cv::aruco::ArucoDetector detector(dictionary, detectorParams);

While writing this line of code, vscode can provide automatic completion and allow me to navigate to the definition file of this function.BUT when I compile, an error occurs.

error: ‘ArucoDetector’ is not a member of ‘cv::aruco’

How can I resolve this issue? What caused this problem?

My code is as follows.

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


//#include <opencv2/objdetect/aruco_detector.hpp>

#include <Eigen/Dense>
#include <iostream>

#include "ros/ros.h"
#include "sensor_msgs/Image.h"
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>


static const std::string OPENCV_WINDOW = "Image window";

class ImageConverter
{
    ros::NodeHandle nh_;
    image_transport::ImageTransport it_;
    image_transport::Subscriber image_sub_;
public:
    ImageConverter()
    : it_(nh_)
    {
        // Subscrive to input video feed and publish output video feed
        image_sub_ = it_.subscribe("/robot/camera/image", 1,&ImageConverter::imageCb, this);
        cv::namedWindow(OPENCV_WINDOW);
    }
     ~ImageConverter()
    {
        cv::destroyWindow(OPENCV_WINDOW);
    }
 
    void imageCb(const sensor_msgs::ImageConstPtr& msg)
    {
        cv_bridge::CvImagePtr cv_ptr;
        try
        {
            cv_ptr = cv_bridge::toCvCopy(msg, sensor_msgs::image_encodings::BGR8);
        }
        catch (cv_bridge::Exception& e)
        {
            ROS_ERROR("cv_bridge exception: %s", e.what());
            return;
        }

        cv::Mat img =  cv_ptr->image;
        cv::Mat img_copy = img.clone();
        cv::Mat img_gray;
        //cv::imshow("test_opencv", img);
        cv::cvtColor(img, img_gray, cv::COLOR_BGR2GRAY);

        cv::aruco::DetectorParameters detectorParams = cv::aruco::DetectorParameters();
        cv::aruco::Dictionary dictionary = cv::aruco::getPredefinedDictionary(cv::aruco::DICT_6X6_250);
        cv::aruco::ArucoDetector detector(dictionary, detectorParams);
  }
};

int main(int argc, char *argv[])
{
    ros::init(argc, argv, "opencv_test");
    ImageConverter ic;
    ros::spin();
    return 0;
}

The error message is as follows.

/home/zhilinxu/catkin_ws_webots/src/vis_ser_demo01/src/main.cpp: In member function ‘void ImageConverter::imageCb(const ImageConstPtr&)’:
/home/zhilinxu/catkin_ws_webots/src/vis_ser_demo01/src/main.cpp:94:20: error: ‘ArucoDetector’ is not a member of ‘cv::aruco’
   94 |         cv::aruco::ArucoDetector detector(dictionary, detectorParams);
      |                    ^~~~~~~~~~~~~
make[2]: *** [vis_ser_demo01/CMakeFiles/demo01.dir/build.make:63: vis_ser_demo01/CMakeFiles/demo01.dir/src/main.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:902: vis_ser_demo01/CMakeFiles/demo01.dir/all] Error 2
make: *** [Makefile:141: all] Error 2
Invoking "make -j20 -l20" failed

It seems that cv::aruco::ArucoDetector is defined in the header file opencv2/objdetect/aruco_detector.hpp, which is already included in opencv2/aruco.hpp. When attempting to directly include opencv2/objdetect/aruco_detector.hpp in my code, I encountered redefinition errors during compilation.

In my code, both cv::aruco::DetectorParameters and cv::aruco::Dictionary are from opencv2/objdetect/aruco_detector.hpp, yet they compile fine. It's quite odd.

Answer 1

I too had this problem (though I was using cv 4.5), and found that the api seems to have changed

Instead of this (from the opencv example):

cv::aruco::DetectorParameters detectorParams = cv::aruco::DetectorParameters();
cv::aruco::Dictionary dictionary = cv::aruco::getPredefinedDictionary(cv::aruco::DICT_6X6_250);

cv::aruco::ArucoDetector detector(dictionary, detectorParams);

detector.detectMarkers(inputImage, markerCorners, markerIds);

We end up with this:

cv::Ptr<cv::aruco::Dictionary> dictionary = cv::aruco::getPredefinedDictionary(cv::aruco::DICT_6X6_250);
cv::aruco::detectMarkers(inputImage, dictionary, markerCorners, markerIds);

Notice the use of cv::Ptr for the dictionary, and the static function detectMarkers (no need to instantiate a detector)