[advanced ROS] Lesson 6 recording and playback in ROS (rosbag)

【ROS Advanced 】 About 6 ROS Recording and playback in （rosbag）

Preface

In advanced ROS tutorial , We plan to introduce and use some functional components , In the previous blog, we had a deep appreciation TF2 How to use the function pack , It has laid a foundation for robot learning in the future , This article is relatively easy , Emphasis on the ROS Finish in Tools for data recording and playback ：rosbag.

One 、 Tool is introduced

• Concept ：ROS Used in the system to realize Recording and playback ROS topic of conversation The toolset of ;

• The essence ：rosbag It's essentially one ROS Subscribe or publish nodes ;

Record data ： Subscribe to topic information in real time and write data to files ,
Playback data ： Read the file , Publish the data information in the file .

• effect ： Data reuse , That is, collecting data is convenient for delaying analysis and debugging , It is useful for the analysis of sensor data in the future ;

• Reference website ：ROS Wiki ROSBAG

Two 、 Common command line instructions

• According to the recording and playback steps ：

1. Prepare the work environment ：
   Create a recording file directory ：mkdir ./xxx and cd xxx
2. Start recording ：

rosbag record -a -O  Target file 

3. see file ：

rosbag info  file name 

4. Playback file ：

rosbag play  file name 

3、 ... and 、 Programming to realize

This section mainly introduces the use of C++ Language programming implementation rosbag Recording and playback process ：

• Admission rosbag file ：

#include "ros/ros.h"
#include "rosbag/bag.h"
#include "std_msgs/String.h"


int main(int argc, char *argv[])
{
    
    ros::init(argc,argv,"bag_write");
    ros::NodeHandle nh;
    // establish bag object 
    rosbag::Bag bag;
    // open 
    bag.open("/home/rosdemo/demo/test.bag",rosbag::BagMode::Write);
    // Write 
    std_msgs::String msg;
    msg.data = "hello world";
    bag.write("/chatter",ros::Time::now(),msg);
    bag.write("/chatter",ros::Time::now(),msg);
    bag.write("/chatter",ros::Time::now(),msg);
    bag.write("/chatter",ros::Time::now(),msg);
    // close 
    bag.close();

    return 0;
}

• Read rosbag file ：

/*  Read  bag  file ： */
#include "ros/ros.h"
#include "rosbag/bag.h"
#include "rosbag/view.h"
#include "std_msgs/String.h"
#include "std_msgs/Int32.h"

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

    setlocale(LC_ALL,"");

    ros::init(argc,argv,"bag_read");
    ros::NodeHandle nh;

    // establish  bag  object 
    rosbag::Bag bag;
    // open  bag  file 
    bag.open("/home/rosdemo/demo/test.bag",rosbag::BagMode::Read);
    // Reading data 
    for (rosbag::MessageInstance const m : rosbag::View(bag))
    {
    
        std_msgs::String::ConstPtr p = m.instantiate<std_msgs::String>();
        if(p != nullptr){
    
            ROS_INFO(" Read data :%s",p->data.c_str());
        }
    }

    // Close file stream 
    bag.close();
    return 0;
}

summary

• Statement ： The blog section of this section refers to CSDN User zhaoxuzuo ROS course , From the next blog ROS The advanced tutorial will first turn to the study of some knowledge of robots , After mastering the establishment method of basic robot model , On the one hand, bloggers will introduce some knowledge about quadruped robots , On the other hand, it will start from URDF Document and GAZEBO Start with simulation , Continue to complete for ROS Learning from , Coming soon .