Rosanswers logo

I'm following these tutorials to stream images to OpenCV format from the /ardrone/image_raw topic.


However, even though I've been able to successfully compile the driver, when i run it, I don't see any images on screen. My code is this -

#include "ros/ros.h"
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>
#include <sensor_msgs/image_encodings.h>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include "ardrone_autonomy/Navdata.h"

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

class ImageConverter
  ros::NodeHandle nh_;
  image_transport::ImageTransport it_;      //ImageTransport object "it_" under the namespace 'image_transport'
  image_transport::Subscriber image_sub_;       //Subscriber object "image_sub_"
  image_transport::Publisher image_pub_;        // Publisher object "image_pub_"
    ImageConverter(): it_(nh_)
        // Subscribe to input video feed and publish output video feed
      image_sub_ = it_.subscribe("/ardrone/image_raw", 1,&ImageConverter::imageCb, this);
      image_pub_ = it_.advertise("/image_converter/output_video", 1);



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

    // Draw an example circle on the video stream
    if (cv_ptr->image.rows > 60 && cv_ptr->image.cols > 60)
      cv::circle(cv_ptr->image, cv::Point(50, 50), 10, CV_RGB(255,0,0));

    // Update GUI Window
    cv::imshow(OPENCV_WINDOW, cv_ptr->image);
    // Output modified video stream

int main(int argc, char** argv)
  ros::init(argc, argv, "see_image");
  ImageConverter ic;
  return 0;

After executing this, rosrun [package_name] [driver_node] along with a recorded .bag file, it is supposed to produce image stream with a circle on it.

I can see when I run rqt_graph both the bag file and the driver node. However, I don't see any image. What am I missing? I've lost about a week in looking at this.

Originally posted by voladoddi on ROS Answers with karma: 87 on 2014-09-26

Post score: 0


1 Answer 1


Rosanswers logo

For those who are stuck in the same position as me, you might want to check your bag file. Mine didn't have any images in them.

But I got stuck here for a while because /ardrone/image_raw was displayed when I called rostopic list. In this case you want to make sure that your images were considerable in message numbers.

  1. Check your rosbag using rosbag info [bag_file] to see if the message is listed.
  2. Try visualizing in rviz if the image is displayed while running the bag file.
  3. rqt_graph for connection of topics.


Originally posted by voladoddi with karma: 87 on 2014-09-26

This answer was ACCEPTED on the original site

Post score: 0


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.