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ROS 笔记（04）— 创建工作空间与功能包、package.xml、CMakelists.txt

1. 工作空间

工作空间 workspace 是一个存放工程开发相关文件的文件夹，主要由以下几个部分组成：

src ：代码空间 Source Space，存放功能包，所有功能包的代码及配置文件；
build ：编译空间 Build Space，存放编译过程中产生的中间文件；
devel ：开发空间 Development Space，存放编译生成的可执行文件，包括一些脚本；
install ：安装空间 Install Space，安装指定的目标位置；

ROS 文件系统级指的是在硬盘上 ROS 源代码的组织形式，其结构大致可以如下图所示：

WorkSpace --- 自定义的工作空间

    |--- build:编译空间，用于存放CMake和catkin的缓存信息、配置信息和其他中间文件。

    |--- devel:开发空间，用于存放编译后生成的目标文件，包括头文件、动态&静态链接库、可执行文件等。

    |--- src: 源码

        |-- package：功能包(ROS基本单元)包含多个节点、库与配置文件，包名所有字母小写，只能由字母、数字与下划线组成

            |-- CMakeLists.txt 配置编译规则，比如源文件、依赖项、目标文件

            |-- package.xml 包信息，比如:包名、版本、作者、依赖项...(以前版本是 manifest.xml)

            |-- scripts 存储python文件

            |-- src 存储C++源文件

            |-- include 头文件

            |-- msg 消息通信格式文件

            |-- srv 服务通信格式文件

            |-- action 动作格式文件

            |-- launch 可一次性运行多个节点 

            |-- config 配置信息

        |-- CMakeLists.txt: 编译的基本配置

catkin 编译系统下的工作空间结构：

2. 创建工作空间

2.1 创建空间

创建空间所用到的命令

$ mkdir -p ~/catkin_ws/src
$ cd ~/catkin_ws/src
$ catkin_init_workspace

其中，catkin_ws 目录名可以任意命名，输入 catkin_init_workspace 命令时可以使用 Tab 键自动联想功能，完整示例过程如下：

wohu@wohu-pc:~/project/ros$ mkdir -p ./ros_demo/src
wohu@wohu-pc:~/project/ros$ cd ./ros_demo/src/
wohu@wohu-pc:~/project/ros/ros_demo/src$ catkin_init_workspace 
Creating symlink "/home/wohu/project/ros/ros_demo/src/CMakeLists.txt" pointing to "/opt/ros/melodic/share/catkin/cmake/toplevel.cmake"

2.2 编译工作空间

使用到的命令如下：

$ cd ~/catkin_ws/
$ catkin_make

示例过程如下：

$ catkin_make
Base path: /home/wohu/project/ros/ros_demo
Source space: /home/wohu/project/ros/ros_demo/src
Build space: /home/wohu/project/ros/ros_demo/build
Devel space: /home/wohu/project/ros/ros_demo/devel
Install space: /home/wohu/project/ros/ros_demo/install
####
#### Running command: "cmake /home/wohu/project/ros/ros_demo/src -DCATKIN_DEVEL_PREFIX=/home/wohu/project/ros/ros_demo/devel -DCMAKE_INSTALL_PREFIX=/home/wohu/project/ros/ros_demo/install -G Unix Makefiles" in "/home/wohu/project/ros/ros_demo/build"
####
-- The C compiler identification is GNU 7.5.0
-- The CXX compiler identification is GNU 7.5.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Using CATKIN_DEVEL_PREFIX: /home/wohu/project/ros/ros_demo/devel
-- Using CMAKE_PREFIX_PATH: /opt/ros/melodic
-- This workspace overlays: /opt/ros/melodic
-- Found PythonInterp: /usr/bin/python2 (found suitable version "2.7.17", minimum required is "2") 
-- Using PYTHON_EXECUTABLE: /usr/bin/python2
-- Using Debian Python package layout
-- Using empy: /usr/bin/empy
-- Using CATKIN_ENABLE_TESTING: ON
-- Call enable_testing()
-- Using CATKIN_TEST_RESULTS_DIR: /home/wohu/project/ros/ros_demo/build/test_results
-- Found gtest sources under '/usr/src/googletest': gtests will be built
-- Found gmock sources under '/usr/src/googletest': gmock will be built
-- Found PythonInterp: /usr/bin/python2 (found version "2.7.17") 
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - not found
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE  
-- Using Python nosetests: /usr/bin/nosetests-2.7
-- catkin 0.7.29
-- BUILD_SHARED_LIBS is on
-- BUILD_SHARED_LIBS is on
-- Configuring done
-- Generating done
-- Build files have been written to: /home/wohu/project/ros/ros_demo/build
####
#### Running command: "make -j12 -l12" in "/home/wohu/project/ros/ros_demo/build"
####
wohu@wohu-pc:~/project/ros/ros_demo$

2.3 设置环境变量

$ source devel/setup.bash

2.4 检查环境变量

$ echo #ROS_PACKAGE_PATH

示例如下：

$ echo $ROS_PACKAGE_PATH
/home/wohu/project/ros/ros_demo/src:/opt/ros/melodic/share
wohu@wohu-pc:~/project/ros/ros_demo$

以上步骤完成后，生成的整体目录文件结构如下：

build 目录文件如下：

devel 目录文件如下：

3. 创建功能包

3.1 创建功能包

$ cd ~/catkin_ws/src
$ catkin_create_pkg <package_name> [depend1] [depend2] [depend3]

完整示例命令如下：

$ catkin_create_pkg test_pkg std_msgs rospy roscpp
Created file test_pkg/package.xml
Created file test_pkg/CMakeLists.txt
Created folder test_pkg/include/test_pkg
Created folder test_pkg/src
Successfully created files in /home/wohu/project/ros/ros_demo/src/test_pkg. Please adjust the values in package.xml.
wohu@wohu-pc:~/project/ros/ros_demo/src$

功能包目录结构：

3.2 编译功能包

$ cd ~/catkin_ws
$ catkin_make
$ source ~/catkin_ws/devel/setup.bash