making a ros node from a qt thread - qt

Question

I have a qt thread in my application which emits a Mat type image so that other threads can use it. the image is coming from camera by using VideoCapture Object of opencv library. now what i intend to do is getting this image from a rostopic, not from camera directly. in order to do that i must create a ros node in my thread and here i am stuck. is there anyone who has the experience to integrate ros node and qt?
here is my thread:
#include "../include/Ground_Station/camera.h"
#include <iostream>
using namespace std;
Camera::Camera()
{
}
void Camera::run()
{
VideoCapture cap;
cap.open(0);
while(1){
Mat image;
cap >> image;
cvtColor(image,image,CV_BGR2RGB);
emit ImgSignal(&image);
QThread::msleep(30);
}
}
and Camera.h:
#ifndef CAMERA_H
#define CAMERA_H
#include <QObject>
#include <QThread>
#include <QtCore>
#include <QtGui>
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>
#include <ros/ros.h>
#include <opencv2/opencv.hpp>
using namespace cv;
class Camera: public QThread
{
Q_OBJECT
public:
Camera();
void run();
bool Stop = false;
signals:
void ImgSignal(Mat*);
private:
public slots:
};
#endif // THREAD_H

Answer 1

Basically, your executable file containing the main() function must be your ros node and your QT application at the same time. In your "main.cpp"
you call ros::init(...) and subscribe to the topic you want to listen to. Your subscriber callback function may convert the ros image to Mat and emmit an ImgSignal every time it is called. To do all that, I'd create a RosImageProvider class, something along the lines ..
class RosImageProvider: public QObject
{
Q_OBJECT
public:
void ImageSubscriberCallback(const sensor_msgs::Image::ConstPtr& img);
...
signals:
void ImgSignal(Mat*);
};

Answer 2

I encountred the same problem when dealing with TCP/IP connection from a ROS node within Qt and my solution was to inherit directly from the QThread object, thus when initializing the class, you initialize the ROS node and implement the work TODO in callbacks and the thread run() function.
So finally, my code looked something like this :
#ifndef INCLUDE_TCPHANDLER_HPP_
#define INCLUDE_TCPHANDLER_HPP_
#include <ros/ros.h>
#include <QThread>
#include <string>
class TCP_Handler : public QThread
{
Q_OBJECT
private:
int init_argc;
char** init_argv;
ros::Publisher cmd_control_publisher;
ros::Subscriber feedback_subscriber;
public:
TCP_Handler()
{}
virtual ~TCP_Handler(){}
/**
* #brief ROS methods
*
*/
inline bool init_ros()
{
int argc =0; char** argv = new char*();
ros::init(argc,argv,"tcp_handler");
ros::NodeHandle n;
cmd_control_publisher = n.advertise<robot_common::cmd_control>("cmd_control", 1000);
feedback_subscriber = n.subscribe<robot_common::feedback>("wifibot_pose", 4, &TCP_Handler::FeedbackCallback , this);
return true;
}
void FeedbackCallback(const robot_common::feedback::ConstPtr& pose)
{
//.....
}
/**
* #brief Threading methods
*
*/
virtual void init(int, std::string ip_addr = "127.0.0.1") = 0;
virtual void run() = 0;
virtual void stop() = 0;
/**
* #brief TCP methods (Server/Client have to implement these folks)
*
*/
virtual bool Send_data(char* data, int size) = 0;
virtual int Receive_data(char* in_data, int size) = 0;
virtual bool Open_connection() = 0;
virtual void Close_connection() = 0;
};
#endif /* INCLUDE_TCPHANDLER_HPP_ */
This code is just a template of a Qt-threaded-ROS node for TCP connction as I don't know your specific needs. feel free to build your own !
Cheers,