0 ROS framework

Just ROS In terms of its own implementation , Its architecture is divided into three layers ：

1. file system
   ROS File system level refers to the view on the hard disk ROS The organization of source code .
2. Calculation chart
   ROS Different processes in distributed system need data interaction , The computing graph can represent the data interaction process in the form of point-to-point network , Important concepts in calculation diagram : node (Node)、 news (message)、 Communication mechanism _ The theme (topic)、 Communication mechanism _ service (service).
3. The open source community
   ROS There are many open source communities , Include ROS WIKI、ROS Answer etc. .

1 ROS file system

ROS File system level refers to on the hard disk ROS The organization of source code , Its structure can be roughly as shown in the figure below ：

The specific meaning of the representative is as follows ：

WorkSpace ---  Custom workspace 

    |--- build: Compilation space , To hold CMake and catkin Cache information for 、 Configuration information and other intermediate files .

    |--- devel: Development space , Used to store the target file generated after compilation , Including header files 、 dynamic & Static link library 、 Executable documents, etc .

    |--- src:  Source code 

        |-- package： Function pack (ROS Basic unit ) Contain multiple nodes 、 Libraries and profiles , All the letters of the package name are lowercase , Only letters 、 Numbers and underscores make up 

            |-- CMakeLists.txt  Configure Compilation Rules , Such as source files 、 Dependencies 、 Target file 

            |-- package.xml  Package information , such as : Package name 、 edition 、 author 、 Dependencies ...( The previous version was  manifest.xml)

            |-- scripts  Storage python file 

            |-- src  Storage C++ Source file 

            |-- include  The header file 

            |-- msg  Message communication format file 

            |-- srv  Service communication format file 

            |-- action  Action format file 

            |-- launch  Multiple nodes can be run at one time  

            |-- config  Configuration information 

        |-- CMakeLists.txt:  Basic configuration of compilation 

Next, we mainly introduce package.xml And CMakeLists.txt These two profiles .

1.1 package.xml

This file defines the properties of the package , For example, package name , Version number , author , Maintainers and others catkin Package dependencies .

​<?xml version="1.0"?>
<!--  Format :  It used to be  1, Recommended format  2 -->
<package format="2">
  <!--  Package name  -->
  <name>demo01_hello_vscode</name>
  <!--  edition  -->
  <version>0.0.0</version>
  <!--  Description information  -->
  <description>The demo01_hello_vscode package</description>

  <!-- One maintainer tag required, multiple allowed, one person per tag -->
  <!-- Example: -->
  <!-- <maintainer email="[email protected]">Jane Doe</maintainer> -->
  <!--  maintenance staff  -->
  <maintainer email="[email protected]">xuzuo</maintainer>


  <!-- One license tag required, multiple allowed, one license per tag -->
  <!-- Commonly used license strings: -->
  <!-- BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
  <!--  License information ,ROS The core component defaults to  BSD -->
  <license>TODO</license>


  <!-- Url tags are optional, but multiple are allowed, one per tag -->
  <!-- Optional attribute type can be: website, bugtracker, or repository -->
  <!-- Example: -->
  <!-- <url type="website">http://wiki.ros.org/demo01_hello_vscode</url> -->


  <!-- Author tags are optional, multiple are allowed, one per tag -->
  <!-- Authors do not have to be maintainers, but could be -->
  <!-- Example: -->
  <!-- <author email="[email protected]">Jane Doe</author> -->


  <!-- The *depend tags are used to specify dependencies -->
  <!-- Dependencies can be catkin packages or system dependencies -->
  <!-- Examples: -->
  <!-- Use depend as a shortcut for packages that are both build and exec dependencies -->
  <!-- <depend>roscpp</depend> -->
  <!-- Note that this is equivalent to the following: -->
  <!-- <build_depend>roscpp</build_depend> -->
  <!-- <exec_depend>roscpp</exec_depend> -->
  <!-- Use build_depend for packages you need at compile time: -->
  <!-- <build_depend>message_generation</build_depend> -->
  <!-- Use build_export_depend for packages you need in order to build against this package: -->
  <!-- <build_export_depend>message_generation</build_export_depend> -->
  <!-- Use buildtool_depend for build tool packages: -->
  <!-- <buildtool_depend>catkin</buildtool_depend> -->
  <!-- Use exec_depend for packages you need at runtime: -->
  <!-- <exec_depend>message_runtime</exec_depend> -->
  <!-- Use test_depend for packages you need only for testing: -->
  <!-- <test_depend>gtest</test_depend> -->
  <!-- Use doc_depend for packages you need only for building documentation: -->
  <!-- <doc_depend>doxygen</doc_depend> -->
  <!--  Dependent build tools , It's a must  -->
  <buildtool_depend>catkin</buildtool_depend>

  <!--  Specify the packages required to build this package  -->
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>

  <!--  Specify the package required to build the library based on this package  -->
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>

  <!--  The package needed to run the code in this package  -->  
  <exec_depend>roscpp</exec_depend>
  <exec_depend>rospy</exec_depend>
  <exec_depend>std_msgs</exec_depend>


  <!-- The export tag contains other, unspecified, tags -->
  <export>
    <!-- Other tools can request additional information be placed here -->

  </export>
</package>

1.2 CMakelists.txt

file CMakeLists.txt yes CMake Input for building the system , Used to build software packages .

​cmake_minimum_required(VERSION 3.0.2) # what is needed  cmake  edition 
project(demo01_hello_vscode) # Package name , Will be  ${
    PROJECT_NAME}  Method call 

## 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
# Set up the software package needed for the build 
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
)

## System dependencies are found with CMake's conventions
# Add system dependency by default 
# 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
#  start-up  python  Module support 
# catkin_python_setup()

################################################
## Declare ROS messages, services and actions ##
##  Statement  ROS  news 、 service 、 action ... ##
################################################

## 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 nonetheless:
##     * 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 、 Service dependent packages 
# generate_messages(
#   DEPENDENCIES
#   std_msgs
# )

################################################
## Declare ROS dynamic reconfigure parameters ##
##  Statement  ROS  Dynamic parameter configuration  ##
################################################

## 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 ##
## 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
#  Runtime dependency 
catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES demo01_hello_vscode
#  CATKIN_DEPENDS roscpp rospy std_msgs
#  DEPENDS system_lib
)

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

## Specify additional locations of header files
## Your package locations should be listed before other locations
#  Add the header file path , The header file path of the current package precedes other file paths 
include_directories(
# include
  ${
    catkin_INCLUDE_DIRS}
)

## Declare a C++ library
#  Statement  C++  library 
# add_library(${
    PROJECT_NAME}
#   src/${
    PROJECT_NAME}/demo01_hello_vscode.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
#  To add a library  cmake  Target dependence 
# 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
#  Statement  C++  Executable file 
add_executable(Hello_VSCode src/Hello_VSCode.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"
# rename c++ Executable file 
# 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 executable file  cmake  Target dependence 
add_dependencies(Hello_VSCode ${
    ${
    PROJECT_NAME}_EXPORTED_TARGETS} ${
    catkin_EXPORTED_TARGETS})

## Specify libraries to link a library or executable target against
# Specify the library 、 Link library of executable files 
target_link_libraries(Hello_VSCode
  ${
    catkin_LIBRARIES}
)

#############
## Install ##
##  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
# Set the executable script for installation 
catkin_install_python(PROGRAMS
  scripts/Hi.py
  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_demo01_hello_vscode.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)

2 ROS File system related commands

ROS File systems are essentially operating system files , We can use Linux Command to manipulate these files , however , stay ROS For better user experience ,ROS Specifically provides something similar to Linux The order of , These commands are compared to Linux Native command , More introduction 、 Efficient . File operations , It's nothing more than adding, deleting, modifying, checking and executing , Next , Let's start from these five dimensions , To introduce ROS Some common commands of file system .

2.1 increase

catkin_create_pkg  Custom package name   Dependency package  ===  Create a new ROS Function pack 
sudo apt install xxx ===  install  ROS Function pack 

2.2 Delete

sudo apt purge xxx ====  Delete a feature pack 

2.3 check

rospack list ===  List all feature packs 
rospack find  Package name  ===  Find out if a feature package exists , If present, return to the installation path 
roscd  Package name  ===  Enter a function package 
rosls  Package name  ===  List the files under a package 
apt search xxx ===  Search for a feature pack 

2.4 Change

rosed  Package name   file name  ===  Modify the function pack file 

2.5 perform

roscore
 Use roscore  Will start :
	ros master
	ros  Parameter server 
	rosout  Log nodes 
rosrun
rosrun  Package name   Executable file name  ===  Run the specified ROS node 
eg:rosrun turtlesim turtlesim_node
roslaunch
roslaunch  Package name  launch file name  ===  Execute... Under a package  launch  file 

3 ROS Calculation chart

3.1 Introduction to the calculation chart

Previously introduced ROS File structure , It's on disk ROS The storage structure of the program , Is static , and ros After the program runs , Different nodes are intricate ,ROS Provides a practical tool rqt_graph A dynamic graph used to display the current system operation .
ROS Different processes in distributed system need data interaction , The computing graph can represent the data interaction process in the form of point-to-point network .rqt_graph yes rqt Part of the package .

3.2 Calculation diagram demonstration

Start three terminals first , Enter the following commands respectively ：

 terminal 1 type :roscore
 terminal 2 type :rosrun turtlesim turtlesim_node( The graphical interface will pop up )
 terminal 3 type :rosrun turtlesim turtle_teleop_key( stay 3 Can be controlled by keyboard 2 The movement of the tortoise in )

Start another terminal , Input

rqt_graph

You can see the network topology diagram similar to the following figure , The diagram can show the relationship between different nodes .