Subscribe to topics from rosbag–take images as an example

This article is a supplement to the CSDN blog that uses the subscription function of ROS topics to extract information from bag files_rosbag extracts multiple topic information.

ROS creates workspace code with one click

conda deactivate # if necessary

# Check path
echo "the current space is "
pwd

#Initialize workspace
mkdir -p ./rosbag-ext/src
cd ./rosbag-ext/src
catkin_init_workspace

cd..
catkin_make -DPYTHON_EXECUTABLE=/usr/bin/python3

# Set environment variables
source ./devel/setup.bash
echo "the ros path is" # Check environment variables
echo $ROS_PACKAGE_PATH

# catkin_create_pkg <package_name> [depend_1] [depend_2] [depend_n]
# Function package
# Where extract is the function package name, followed by dependencies
catkin_create_pkg extract cv_bridge roscpp std_msgs sensor_msgs

# Compile function package
catkin_make
source ./devel/setup.bash

Code for subscribing to topics

//This code is used to get the topic in rosbag
#include <ros/ros.h>
#include<sensor_msgs/Image.h>
#include <opencv2/opencv.hpp>
#include<cv_bridge/cv_bridge.h>
#include<iostream>
#include<string>
#include<vector>

using namespace std;
vector<double> image_times;
vector<cv::Mat> images;

string yaml = "/home/nm/ros-learn/rosbag-ext/src/extract/src/topicpath.yaml";
string ImageTopic;
string ImagePath;
string TimePath;
int i = 0;

void readParameters(ros::NodeHandle &n)
{
    std:string config_file;
    config_file = yaml;
    cv::FileStorage fsSettings(config_file, cv::FileStorage::READ);
    if(! fsSettings.isOpened())
    {
        std::cerr << "ERROR: wrong path to settings" << std::endl;
    }
    fsSettings["image_topic"] >> ImageTopic;
    fsSettings["image_path"] >> ImagePath;
    fsSettings["time_path"] >> TimePath;
    fsSettings.release();
}

void imageCallback(const sensor_msgs::ImageConstPtr & amp;img_msg)
{
    cv_bridge::CvImageConstPtr ptr;
    ptr = cv_bridge::toCvCopy(img_msg, img_msg->encoding);
    cv::Mat show_img = ptr -> image;

    string str1, image_path;
    stringstream ss1;

    cout << "sub No." << i << " image from topic" << endl;
    ss1 << i;
    ss1 >> str1;
     + + i;
    image_path = ImagePath + str1 + ".png";
    cv::imwrite(image_path, show_img);

}

// rosrun extract nm_subscriber
int main(int argc, char** argv)
{
    // yaml = argv[1];
    // yaml = "/home/nm/ros-learn/rosbag-ext/src/extract/src/topicpath.yaml";
//Initialize ROS node
ros::init(argc, argv, "nm_image_sub");

    //Create node handle
ros::NodeHandle node;
    readParameters(node);
    cout << "Image Path == " << yaml << endl;

    // ros::Subscriber image_sub = node.subscribe(IMAGE_TOPIC, 1000, imageCallback); // Subscribe to image information
    // ros::Subscriber sub_imu = node.subscribe(IMU_TOPIC, 2000, imu_callback); // Subscribe to imu information
    ros::Subscriber img_sub = node.subscribe(ImageTopic,5000,imageCallback);

    ros::spin();


    return 0;
}

/*
packet rosbag info
path: ./Datasets/MH_01_easy.bag
version: 2.0
duration: 3:06s (186s)
start: Jun 25 2014 03:02:59.81 (1403636579.81)
end: Jun 25 2014 03:06:06.70 (1403636766.70)
size: 2.5 GB
messages: 47283
compression: none [2456/2456 chunks]
types: geometry_msgs/PointStamped [c63aecb41bfdfd6b7e1fac37c7cbe7bf]
             sensor_msgs/Image [060021388200f6f0f447d0fcd9c64743]
             sensor_msgs/Imu [6a62c6daae103f4ff57a132d6f95cec2]
topics: /cam0/image_raw 3682 msgs : sensor_msgs/Image
             /cam1/image_raw 3682 msgs : sensor_msgs/Image
             /imu0 36820 msgs : sensor_msgs/Imu
             /leica/position 3099 msgs : geometry_msgs/PointStamped

*/

YAML stores various addresses

%YAML:1.0

# the save path of image
image_path: "/home/nm/ros-learn/Datasets/temp/image/"


# the name of image topic
image_topic: /cam0/image_raw

# the name of imu topic
imu_topic: /imu0

CMakeLists

cmake_minimum_required(VERSION 3.0.2)
project(extract)

## Compile as C++11, supported in ROS Kinetic and newer
# add_compile_options(-std=c++11)

## Find catkin macros and libraries
## if COMPONENTS list like find_package(catkin REQUIRED COMPONENTS xyz)
## is used, also find other catkin packages
find_package(catkin REQUIRED COMPONENTS
  cv_bridge
  roscpp
  sensor_msgs
  std_msgs
)

## System dependencies are found with CMake's conventions
# find_package(Boost REQUIRED COMPONENTS system)


## Uncomment this if the package has a setup.py. This macro ensures
## modules and global scripts declared therein get installed
## See http://ros.org/doc/api/catkin/html/user_guide/setup_dot_py.html
#catkin_python_setup()

###############################################
## Declare ROS messages, services and actions ##
###############################################

## To declare and build messages, services or actions from within this
## package, follow these steps:
## * Let MSG_DEP_SET be the set of packages whose message types you use in
## your messages/services/actions (e.g. std_msgs, actionlib_msgs, ...).
## * In the file package.xml:
## * add a build_depend tag for "message_generation"
## * add a build_depend and a exec_depend tag for each package in MSG_DEP_SET
## * If MSG_DEP_SET isn't empty the following dependency has been pulled in
## but can be declared for certainty nevertheless:
## * add a exec_depend tag for "message_runtime"
## * In this file (CMakeLists.txt):
## * add "message_generation" and every package in MSG_DEP_SET to
## find_package(catkin REQUIRED COMPONENTS ...)
## * add "message_runtime" and every package in MSG_DEP_SET to
## catkin_package(CATKIN_DEPENDS ...)
## * uncomment the add_*_files sections below as needed
## and list every .msg/.srv/.action file to be processed
## * uncomment the generate_messages entry below
## * add every package in MSG_DEP_SET to generate_messages(DEPENDENCIES ...)

## Generate messages in the 'msg' folder
# add_message_files(
#FILES
#Message1.msg
#Message2.msg
# )

## Generate services in the 'srv' folder
# add_service_files(
#FILES
# Service1.srv
# Service2.srv
# )

## Generate actions in the 'action' folder
# add_action_files(
#FILES
# Action1.action
# Action2.action
# )

## Generate added messages and services with any dependencies listed here
# generate_messages(
#DEPENDENCIES
# sensor_msgs# std_msgs
# )

###############################################
## Declare ROS dynamic reconfigure parameters ##
###############################################

## To declare and build dynamic reconfigure parameters within this
## package, follow these steps:
## * In the file package.xml:
## * add a build_depend and a exec_depend tag for "dynamic_reconfigure"
## * In this file (CMakeLists.txt):
## * add "dynamic_reconfigure" to
## find_package(catkin REQUIRED COMPONENTS ...)
## * uncomment the "generate_dynamic_reconfigure_options" section below
## and list every .cfg file to be processed

## Generate dynamic reconfigure parameters in the 'cfg' folder
# generate_dynamic_reconfigure_options(
#cfg/DynReconf1.cfg
#cfg/DynReconf2.cfg
# )

###################################
## catkin specific configuration ##
###################################
## The catkin_package macro generates cmake config files for your package
## Declare things to be passed to dependent projects
## INCLUDE_DIRS: uncomment this if your package contains header files
## LIBRARIES: libraries you create in this project that dependent projects also need
## CATKIN_DEPENDS: catkin_packages dependent projects also need
## DEPENDS: system dependencies of this project that dependent projects also need
catkin_package(
# INCLUDE_DIRS include
# LIBRARIES extract
 CATKIN_DEPENDS cv_bridge roscpp sensor_msgs std_msgs
# DEPENDS system_lib
)

###########
## Build ##
###########

## Specify additional locations of header files
## Your package locations should be listed before other locations
include_directories(
#include
  ${catkin_INCLUDE_DIRS}
)

## Declare a C++ library
# add_library(${PROJECT_NAME}
# src/${PROJECT_NAME}/extract.cpp
# )

## Add cmake target dependencies of the library
## as an example, code may need to be generated before libraries
## either from message generation or dynamic reconfigure
# add_dependencies(${PROJECT_NAME} ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})

## Declare a C++ executable
## With catkin_make all packages are built within a single CMake context
## The recommended prefix ensures that target names across packages don't collide
# add_executable(${PROJECT_NAME}_node src/extract_node.cpp)

## Rename C++ executable without prefix
## The above recommended prefix causes long target names, the following renames the
## target back to the shorter version for ease of user use
## e.g. "rosrun someones_pkg node" instead of "rosrun someones_pkg someones_pkg_node"
# set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX "")

## Add cmake target dependencies of the executable
## same as for the library above
# add_dependencies(${PROJECT_NAME}_node ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})

## Specify libraries to link a library or executable target against
# target_link_libraries(${PROJECT_NAME}_node
# ${catkin_LIBRARIES}
# )

add_executable(nm_subscriber /home/nm/ros-learn/rosbag-ext/src/extract/src/sub.cpp)
target_link_libraries(nm_subscriber ${catkin_LIBRARIES})


#############
## Install ##
#############

# all install targets should use catkin DESTINATION variables
# See http://ros.org/doc/api/catkin/html/adv_user_guide/variables.html

## Mark executable scripts (Python etc.) for installation
## in contrast to setup.py, you can choose the destination
# catkin_install_python(PROGRAMS
# scripts/my_python_script
# DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
# )

## Mark executables for installation
## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_executables.html
# install(TARGETS ${PROJECT_NAME}_node
# RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
# )

## Mark libraries for installation
## See http://docs.ros.org/melodic/api/catkin/html/howto/format1/building_libraries.html
# install(TARGETS ${PROJECT_NAME}
# ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
# LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
# RUNTIME DESTINATION ${CATKIN_GLOBAL_BIN_DESTINATION}
# )

## Mark cpp header files for installation
# install(DIRECTORY include/${PROJECT_NAME}/
# DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
# FILES_MATCHING PATTERN "*.h"
# PATTERN ".svn" EXCLUDE
# )

## Mark other files for installation (e.g. launch and bag files, etc.)
# install(FILES
# # myfile1
# # myfile2
# DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
# )

#############
## Testing ##
#############

## Add gtest based cpp test target and link libraries
# catkin_add_gtest(${PROJECT_NAME}-test test/test_extract.cpp)
# if(TARGET ${PROJECT_NAME}-test)
# target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME})
#endif()

## Add folders to be run by python nosetests
#catkin_add_nosetests(test)