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Rosbags saving empty messages

asked 2019-02-22 17:26:17 -0500

stevenjediknight gravatar image

updated 2019-02-22 18:52:41 -0500

jayess gravatar image

I am trying to record data from data from a Razor 9DOF imu, Hokuyo LIDAR and a ZED camera. The code compiles and runs fine but it is saving empty messages to the rosbag file. I have tried printing data in at different points and it wont. Can you tell me what my code is missing and why the messages are empty? I am running ROS kinetic 1.12.14 on Ubuntu 16.04 on an Nvidia Jetson TX2.

#include <iostream>
#include <ros/ros.h>
#include <rosbag/bag.h>
#include <sensor_msgs/Imu.h>
#include <sensor_msgs/LaserScan.h>
#include <sensor_msgs/Image.h>

sensor_msgs::Imu    imu_msg;
sensor_msgs::LaserScan scan;
sensor_msgs::Image msgr;
sensor_msgs::Image msgl;

   void imuCallback(const sensor_msgs::Imu &imu_msg)


  void scanCallback(const sensor_msgs::LaserScan::ConstPtr& scan)


  void imageRightRectifiedCallback(const sensor_msgs::Image &msgr) {


  void imageLeftRectifiedCallback(const sensor_msgs::Image &msgl) {


int main(int argc, char** argv){

    ros::init(argc, argv, "talker"); 
    ros::NodeHandle n; 

    rosbag::Bag bag; // create a bag named bag"data.bag", rosbag::bagmode::Write); //open bag and create a file to save to.

    ros::Subscriber imu_sub = n.subscribe("imu_data", 1000, imuCallback); // subscribes to the imu and start the callback function
    ros::Subscriber sub = n.subscribe<sensor_msgs::LaserScan>("/scan", 1000, scanCallback); // subscribes to the lidar and start the callback function
    // subscribes to the zed and get the right image and start the callback function
    ros::Subscriber subRightRectified = n.subscribe("/zed/right/image_rect_color", 10, imageRightRectifiedCallback); 
    // subscribes to the zed and get the left image and start the callback function
    ros::Subscriber subLeftRectified = n.subscribe("/zed/left/image_rect_color", 10, imageLeftRectifiedCallback); 
       bag.write("imu", ros::Time::now(), imu_msg); // sending msg into the bag
       bag.write("lidar", ros::Time::now(), scan);
       bag.write("ZED_RightImage", ros::Time::now(), msgr);
       bag.write("ZED_LeftImage", ros::Time::now(), msgl);

        ROS_INFO("Recording data...");
    return 0;
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1 Answer

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answered 2019-02-23 01:44:51 -0500

gvdhoorn gravatar image

Where in your code are you storing incoming msgs in the imu_msg, scan, msgr and msgl global variables?

The bodies of your callbacks are empty, so incoming msgs are never actually processed.

Also: is there any reason you cannot use rosbag itself? That would seem to already be capable of what you are showing here, but without any custom code.

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Sorry could not work on this over the weekend. I assumed const sensor_msgs::LaserScan::ConstPtr& scan would store in the global variables i will try doing tin the call back function. the reason I am writing this is to run one command and have a rosbag for playback and .cvs files.

stevenjediknight gravatar image stevenjediknight  ( 2019-02-25 10:29:34 -0500 )edit

Personally I would still use rosbag and then afterwards post-process that into a .csv file, but it's up to you of course.

gvdhoorn gravatar image gvdhoorn  ( 2019-02-25 11:06:11 -0500 )edit

It's still not working even after saving the data from callback messages to the global variables. It seems like my callbacks are return empty messages even though i cant rostopic ech /imu and see my data.

stevenjediknight gravatar image stevenjediknight  ( 2019-02-25 14:13:40 -0500 )edit

It could probably work, but you are ros::spinOnce()-ing at the absolute maximum frequency your PC supports (no sleep) which most likely results in many, many duplicate msgs.

Without seeing updated code we cannot help you, but I would say again that it's a little strange to -- basically -- ..

gvdhoorn gravatar image gvdhoorn  ( 2019-02-25 14:16:03 -0500 )edit

.. reimplement what rosbag already does.

gvdhoorn gravatar image gvdhoorn  ( 2019-02-25 14:16:16 -0500 )edit

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Asked: 2019-02-22 17:26:17 -0500

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Last updated: Feb 23 '19