[introduction to ROS] - 03 ROS workspace and function pack

Just like other software learning ,ROS You also need to start with the project , about ROS Come on , At the beginning of the project, you need to create a workspace , Create a feature pack after compiling the build folder , Then continue through the command line , Or programming through code to achieve the goal function , This blog section mainly introduces the contents of the first part , It also briefly introduces the functions of the files in the workspace .

One 、 working space

1. Create a workspace

• Create folder ：mkdir -p ~/catkin_ws/src
  In the above order catkin_ws, Is the name of the workspace , This name will be covered in subsequent courses , So you can also use the appropriate name by yourself ,src Is the folder where the feature pack is placed , For storing source code .
• Switch to src Folder ：cd ~catkin_ws/src
• Create a workspace ：catkin_init_workspace

Command line output prompt ：

Creating symlink "/home/zhaoxu/project/ROS/catkin_ws/src/CMakeLists.txt" pointing to "/opt/ros/noetic/share/catkin/cmake/toplevel.cmake"

• Switch to working directory ：cd ~/catkin_ws/
• Compile workspace ：catkin_make
  there catkin Note that it is independent of the workspace name , It belongs to fixed command , After compilation, the command line indicates as follows ：
  
• Generate install Folder ：catkin_make install
  The instructions here are only intended to be the first to create install file , Essentially meaningless .

2. Set the environment variable

• General practice ： You need to reload each time you open the terminal

source devel/setup.bash

• Once and for all ： stay .bashrc Add a fixed path to the file , There is no need to source

echo "source ~/catkin_ws/devel/setup.bash" >> ~/.bashrc

• Query environment variables ：echo $ROS_PACKAGE_PATH
  The results are as follows , It proves that the modification is successful
  

3. Introduction to workspace

• src： Code space ,Source Space, Used to place feature packs （ Code 、 The configuration file 、launch file ）;
• build： Compilation space ,Build Space, Used to place intermediate files 、 Binary files, etc ;
• devel： Development space ,Development Space, Used to place the executable generated by compilation 、 Script 、 Kuo et al ;
• install： Installation space ,Install Space, Used to place installed files ;

Two 、 Function pack

1. Create and compile feature packs

• Switch to the specified directory ：cd ~/catkin_ws/src
• Create Feature Pack ：catkin_create_pkg pkg_ts std_msgs rospy roscpp

Standard directive ：catkin_create_pkg <package_name> [depend1] [depend2] …
That is to use catkin_create_pkg Instruction to create function pack , Depends on the above three dependencies

• Switch to the workspace Directory ：cd ~catkin_ws
• Compile function packs ：catkin_make

Be careful ： Under the same workspace , A feature pack with the same name is not allowed ; In different workspaces , Feature packs with the same name are allowed

2. Function package file parsing

• include： For placement The header file
• src： For placement Source file
• CMakelist.txt： Compile configuration file , Describe the Compilation Rules of the function package
• package.xml： Feature Pack list file , contain name、version、 Description information 、author email、depend、license etc.

Here we focus on the latter two ：

1）CMakelist.txt

• The function of documents ：CMakeList.txt File is CMake The input file of the compilation process of the compilation system . whatever CMake Compatible packages contain one or more CMakeLists.txt file , These documents describe How to compile the code and where to install it . take CMakeLists.txt File applies to a catkin Project time , It is a standard with some restrictions vanilla CMakeLists.txt file . Use CMake When compiling a program ,cmake Instruction basis CMakeLists.txt File generation makefiles file ,make The order is based on makefiles The file compilation link can generate Executable files

• Supplementary knowledge ：catkin_make, It's actually ROS Compiler system of take cmake and make Unified encapsulated instructions , Therefore, in essence, it is still the use of cmake and make The process of compiling .

• Sequential structure analysis ：

1. CMake edition ：cmake_minimum_required(VERSION 3.0.2)
2. Package name ：project(pkg_ts)
3. Declare dependency Library ：find_package()

4. start-up python Module support ：catkin_python_package()

5. news / service / operation (Message/Service/Action) generator ： add_message_files(),add_service_files(),add_action_files()

6. Call message / service / Operation generation ：generate_messages()

7. Dynamically reconfigure parameters :generate_dynamic_reconfigure_options() ,cfg The configuration file , Used to configure some rviz Format , Record some configuration parameters

8. Specify the export of package compilation information ：catkin_package()

9. a key ： Add libraries and executables to compile ：add_library()/add_executable()/target_link_libraries()

10. Installation rules ：install()

11. Test compilation [ To configure ：catkin_add_gtest()

2）package.xml

The specific explanation here is mainly within the code , See the explanation below ：

<?xml version="1.0"?> 
<!‐‐  At present xml edition  ‐‐> 
<package format="2"> 
<name>learning_cplus</name> 
<!‐‐  The Feature Pack name is learning_cplus,name, name  ‐‐> 
<version>0.0.0</version> 
<!‐‐  The current feature pack version is 0.0.0,version, edition ‐‐> 
<description>The learning_cplus package</description> 
<!‐‐  Introduction to the current feature pack ,description, detailed  ‐‐> 
<maintainer email="[email protected]">waveshare</maintainer> 
<!‐‐  Current maintainer information （ Mailbox and nickname ）‐‐>
<!‐‐ BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 ‐ ‐>
<license>TODO</license> 
<!‐‐  Protocol version , Default TODO Can . You can learn by yourself if you are interested .‐‐> 
<!‐‐ <url type="website">http://wiki.ros.org/learning_cplus</url> ‐‐> 
<!‐‐  Shareable path , You can upload your package to ROS Community or github.‐‐> 
<author email="[email protected]">Jane Doe</author> 
<!‐‐  Current developer information （ Mailbox and nickname ）‐‐> 
<!‐‐ 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 ag ainst 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 documentati on: ‐‐> 
<!‐‐ <doc_depend>doxygen</doc_depend> ‐‐> 
<buildtool_depend>catkin</buildtool_depend> 
<!‐‐ The compiler tool is catkin ‐‐> 
<build_depend>roscpp</build_depend> 
<!‐‐ Compile dependencies roscpp ‐‐> 
<build_depend>rospy</build_depend> 
<!‐‐ Compile dependencies rospy ‐‐> 
<build_depend>std_msgs</build_depend> 
<!‐‐ Compile dependencies std_msgs ‐‐>
<build_export_depend>roscpp</build_export_depend> 
<!‐‐ Compile output dependencies roscpp ‐‐>
<build_export_depend>rospy</build_export_depend> 
<!‐‐ Compile output dependencies rospy ‐‐> 
<build_export_depend>std_msgs</build_export_depend> 
<!‐‐ Compile output dependencies std_msgs ‐‐> 
<exec_depend>roscpp</exec_depend> 
<!‐‐ Operational dependency roscpp ‐‐> 
<exec_depend>rospy</exec_depend> 
<!‐‐ Operational dependency rospy ‐‐> 
<exec_depend>std_msgs</exec_depend>
<!‐‐ Operational dependency std_msgs ‐‐> 
<!‐‐ The export tag contains other, unspecified, tags ‐‐> 
<export> 
<!‐‐ Other tools can request additional information be placed here ‐‐>

<!‐‐  Output  ‐‐> 
</export> 
</package>

summary

This article mainly introduces the workspace 、 The basic content of the function pack , And the process of creating and compiling them ; And in-depth analysis of CMakelist.txt And package.xml Specific content of , The blog content refers to Gu Yueju's ROS introduction 21 Talk to the light snow class ROS Basic series of tutorials , The next blog will mainly introduce how to use the turtle test to analyze the actual effect of each instruction , And simply test the use of programming code , Coming soon .