Read image in main loop instead of imageCallback ?
Hello newbie here,
I am writing an application where I subscribe to an image topic. I followed this tutorial: http://wiki.ros.org/image_transport/T... . It's a great tutorial but it uses a callback function for processing the image. Because I need the image in my main loop, Is it possible to read the image in main? Because when I run my program I only get in the callback function and not the main code below the subscribe function.
6 void imageCallback(const sensor_msgs::ImageConstPtr& msg)
7 {
8 try
9 {
10 cv::imshow("view", cv_bridge::toCvShare(msg, "bgr8")->image);
11 cv::waitKey(30);
12 }
13 catch (cv_bridge::Exception& e)
14 {
15 ROS_ERROR("Could not convert from '%s' to 'bgr8'.", msg->encoding.c_str());
16 }
17 }
18
19 int main(int argc, char **argv)
20 {
21 ros::init(argc, argv, "image_listener");
22 ros::NodeHandle nh;
23 cv::namedWindow("view");
24 cv::startWindowThread();
25 image_transport::ImageTransport it(nh);
26 image_transport::Subscriber sub = it.subscribe("camera/image", 1, imageCallback);
27 ros::spin();
28 cv::destroyWindow("view");
HERE'S SOME CODE THAT USES THE IMAGE DATA FOR PROCESSING (FOR EXAMPLE OPENCV FUNCTIONS)
29 }
Can you please update your question with a copy and paste of what you've done so far (the code)? This will help people to answer question, I believe.
Hello jayess, I've put in the example code of the tutorial and the place where I want to put my code. Thank you for the fast response
Hi, probably you need to define cv image as a global variable then inside the callback function: convert the coming message to cv image using the cv_bridge and then assign it to the global image variable, inside your main you can use the global variable.
Yes I am trying to, but it seems like the application stays in the imagecallback and never returns to main. For now I just have an imshow and waitkey in the callback and print to console in the main.
Well the
waitkey()would certainly do that.I've removed the waitkey, but it still stays in the callback function. Maybe is there something with the ros::spin() that I am doing wrong? I've also tried with a ros::topic::waitForMessage<sensor_msgs::image>, but the video isn't smooth then.
It shouldn't stay in the callback function. But the
ros::spin();will block until you close your node, so any code after that line will only be executed as your node is shutting down. You will need a loop containingros::spinOnce();in main instead.The ros::spinOnce(); works! thank you very much!