从C ++中的类的函数成员返回数组

Question

I'm using ROS and OpenCV in C++ environment in order to acquire a video (gray-scale) from a ROS node, convert the data through cv_bridge (in order to elaborate it through OpenCV), extract some data and publish them on a topic as ROS messages.

My problem is that I don't know how to send the array frame to the main function in order to elaborate it! I cannot elaborate out of it, because I need to distinguish between different data of different frames. This is my code:

#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>
#include <sensor_msgs/image_encodings.h>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <vector>
#include "rd_ctrl/proc_data.h"
#include <cv.h>

using namespace std;
namespace enc = sensor_msgs::image_encodings;


rd_ctrl::proc_data points;

ros::Publisher data_pub_; 

static const char WINDOW[] = "Image window";

class ImageConverter
{
  ros::NodeHandle nh_;
  image_transport::ImageTransport it_;
  image_transport::Subscriber image_sub_;
  image_transport::Publisher image_pub_;

public:
  ImageConverter()
    : it_(nh_)
  {
    image_pub_ = it_.advertise("out", 1);
    image_sub_ = it_.subscribe("/vrep/visionSensorData", 1, &ImageConverter::imageCb, this);


    cv::namedWindow(WINDOW);
  }

  ~ImageConverter()
  {
    cv::destroyWindow(WINDOW);
  }

  void imageCb(const sensor_msgs::ImageConstPtr& msg)
  {
    cv_bridge::CvImagePtr cv_ptr;
    try
    {
      cv_ptr = cv_bridge::toCvCopy(msg, enc::BGR8);
    }
    catch (cv_bridge::Exception& e)
    {
      ROS_ERROR("cv_bridge exception: %s", e.what());
      return;
    }

 CvMat frame= cv_ptr->image;     //definition of "frame"
cvSmooth(&frame, &frame, CV_MEDIAN);
 cvThreshold(&frame, &frame,200, 255,CV_THRESH_BINARY);

    cv::imshow(WINDOW, cv_ptr->image);
    cv::waitKey(3);

    image_pub_.publish(cv_ptr->toImageMsg());
  }
};


int main(int argc, char** argv)
{
  ros::init(argc, argv, "image_proc");
  ImageConverter ic;
ros::NodeHandle n;

//....elaboration of "frame" and production of the data "points"

data_pub_.publish(points);

data_pub_ = n.advertise<rd_ctrl::proc_data>("/data_im", 1);

 ros::spin();
  return 0;
}

I hope that the question is clear enough. Can you help me please?

Answer 1

Now if I understand you correctly you want to call imageCb and have the frame it creates passed back to main . If that is indeed the case then you can modify imageCb as follows:

void imageCb(const sensor_msgs::ImageConstPtr& msg, cv::Mat frame )

You will need to create the frame in main and pass it imageCb :

cv::Mat frame ;
ic.imageCb( ..., frame ) ;

This will use the copy constructor, it will just copy the header and use a pointer to the actual data, so it won't be very expensive.

This previous thread has a much more detailed elaboration on cv::Mat copy constructor.