1 launch文件介绍及简单应用

1.1 launch文件介绍

根据ROS的架构和通信机制来看，ROS的各个功能的实现离不开节点(node)和话题(topic)、参数(parameter)、服务(service)等构成的网络拓扑(rosgraph)，其中每个j节点 都可以完成对应的功能。而一个机器人完整功能的实现，通常需要启动多个节点，如果一个节点一个节点的启动，比较麻烦。官方给出的优化策略是使用 launch 文件，可以一次性启动多个 ROS 节点。通过launch文件以及roslaunch命令可以一次性启动多个节点，并且可以设置丰富的参数。
在官方给出的例程中，发部分功能的实现都是通过launch文件来实现的，我们也应该学会这种优化策略，通过launch文件来启动自己的功能包，高效的实现各种功能。

1.2 launch文件简单应用

1.对于launch文件的存放，我们可以在功能包下新建一个launch文件夹来专门存在launch文件，方便我们进行调用，下面进行实操
VSode在工作空间目录下打开，这里我们打开的是之前演示的VScode_ws工作空间，打开后在功能包下创建launch文件夹即可

2.在launch文件夹下新建一个名为test01的*.launch文件

3.在编写launch文件之前，我们先介绍一下launch文件的格式，launch文件本质是一个xml类型的文件，通过各种标签进行功能的实现，下面列举launch文件的基本格式及各标签的作用
launch文件的基本格式如下：

<launch>
    <node .../>
   	<param .../>
    <rosparam .../>
    <include .../>
    <remap .../>
    <arg .../>
    <group>  </group>
</launch>

launch

<!-- launch 标签是 launch 文件的根节点，它是其他子标签的容器，没有其他特殊功能。 -->
<launch>
	...
</launch>

node
node标签会指定一个准备运行的ROS节点，node标签是 launch 文件中最重要的标签，因为它实现了launch文件的基本功能，即同时启动多个ROS节点。

<node pkg="package_name" type="executable_node" name="node_name" args="$()" respawn="true" output="sceen">

pkg：节点所在功能包的名称package_name；
type：节点类型是可执行文件(节点)的名称executable_node；
name：节点运行时的名称node_name；
args：传递命令行设置的参数；
respawn：是否自动重启，true表示如果节点未启动或异常关闭，则自动重启；false则表示不自动重启，默认值为false；
output：是否将节点信息输出到屏幕，如果不设置该属性，则节点信息会被写入到日志文件，并不会显示到屏幕上。
param
在工程项目开发中，我们常常需要改变程序变量的一些参数，如果在程序中赋值，我们每次修改参数都需要重新编译程序，大大降低了开发效率，而param标签则可以实现传递参数的功能，它可以定义一个将要被设置到参数服务器的参数，它的参数值可以通过文本文件、二进制文件或命令等属性来设置。

<param name="param_name" type="param_type" value="param_value" />
<!-- param 标签可以嵌入到 node 标签中，以此来作为该 node 的私有参数 -->
<node>
	<param name="param_name" type="param_type" value="param_value" />
</node>

name：参数名称param_name
type：参数类型double，str，int，bool，yaml
value：需要设置的参数值param_value
rosparam
rosparam标签可以实现节点从参数服务器上加载(load)、导出(dump)和删除(delete)YAML文件

<!-- 加载package_name功能包下的example.yaml文件 -->
<rosparam command="load" file="$(find package_name)/example.yaml">
<!-- 导出example_out.yaml文件到package_name功能包下 -->
<rosparam command="dump" file="$(find package_name)/example_out.yaml" />
<!-- 删除参数 -->
<rosparam command="delete" param="xxx/param">

command：功能类型(load、dump、delete)
file：参数文件的路径
param：参数名称
include
include标签功能和编程语言中的include预处理类似，它可以导入其他launch文件到当前include标签所在的位置，实现launch文件复用。

<include file="$(find package_name)/launch_file_name">

remap
remap标签可以实现节点名称的重映射，每个remap标签包含一个原始名称和一个新名称，在系统运行后原始名称会被替换为新名称。

<remap from="turtle1/cmd_vel" to="/cmd_vel" />
<!-- remap 标签同样可以嵌入到 node 标签中，以此来作为该 node 的私有重映射 -->
<node>
	<remap from="turtle1/cmd_vel" to="/cmd_vel" />
</node>

arg
arg标签表示启动参数，该标签允许创建更多可重用和可配置的启动文件，其可以通过命令行、include 标签、定义在高级别的文件这 3 种方式配置值。同时注意：arg标签声明的参数不是全局的，只能在声明的单个启动文件中使用，可以当成函数的局部参数来理解。

<arg name="arg_name" default="arg_default" />
<arg name="arg_name" value="arg_value" />
<!-- 命令行传递的 arg 参数可以覆盖 default，但不能覆盖 value。 -->

注意：arg和param标签的区别：

函数	作用
arg	启动时的参数，只在launch文件中有意义
param	运行时的参数，参数会存储在参数服务器中

group
group标签可以实现将一组配置应用到组内的所有节点，它也具有命名空间ns特点，可以将不同的节点放入不同的 namespace。

<!-- 用法1 -->
<group ns="namespace_1">
    <node pkg="pkg_name1" .../>
    <node pkg="pkg_name2" .../>
    ...
</group>

<group ns="namespace_2">
    <node pkg="pkg_name3" .../>
    <node pkg="pkg_name4" .../>
    ...
</group>
<!-- 用法2 -->
<!-- if = value：value 为 true 则包含内部信息 -->
<group if="$(arg foo1)">
    <node pkg="pkg_name1" .../>
</group>

<!-- unless = value：value 为 false 则包含内部信息 -->
<group unless="$(arg foo2)">
    <node pkg="pkg_name2" .../>
</group>
<!--
	当 foo1 == true 时包含其标签内部
	当 foo2 == false 时包含其标签内部
-->

4.下面我们通过几个简单的实例，来演示一下上述函数可以实现的功能

• 通过launch文件同时启动乌龟GUI节点和键盘控制节点，代码如下

<launch>
	<!-- 启动乌龟GUI节点 -->
	<node pkg="turtlesim" type="turtlesim_node" name="Turtle_Gui" output="screen" />
	<!-- 启动键盘控制节点 -->
	<node pkg="turtlesim" type="turtle_teleop_key"  name="Key_Control" output="screen" />
</launch>

终端下launch文件运行格式如下，第一次运行记得使用指令更新环境变量source ./devel/setup.bash

roslaunch 功能包名 launch文件名字.launch

本教程在VScode终端下的指令为：

source ./devel/setup.bash
roslaunch demo01_helloworld_vs test01.launch

运行结果如下，我们可以看到，键盘可以成功控制乌龟运动。

注意：launch文件启动之前，无需再执行roscore指令启动rosmaster，launch文件可以自启动rosmaster

2 package.xml文件介绍及配置

我们以功能包demo01_helloworld_vs下的package.xml文件为例介绍package.xml文件格式及配置

<?xml version="1.0"?>
<!-- 格式: 以前是 1，推荐使用格式 2 -->
<package format="2">
  <!-- 功能包名 -->
  <name>demo01_helloworld_vs</name>
  <!-- 版本 -->
  <version>0.0.0</version>
  <!-- 功能包描述信息 -->
  <description>The demo01_helloworld_vs package</description>

  <!-- One maintainer tag required, multiple allowed, one person per tag -->
  <!-- Example:  -->
  <!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> -->
  <!-- 开发维护人员信息 -->
  <maintainer email="xxx@todo.todo">xxx</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 -->
  <!-- 许可证信息，ROS核心组件默认 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_helloworld_vs</url> -->


  <!-- Author tags are optional, multiple are allowed, one per tag -->
  <!-- Authors do not have to be maintainers, but could be -->
  <!-- Example: -->
  <!-- <author email="jane.doe@example.com">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> -->
  <!-- 依赖的构建工具，这是必须的 -->
  <buildtool_depend>catkin</buildtool_depend>
  
  <!-- 指定构建此软件包所需的软件包 -->
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  
  <!-- 指定根据这个包构建库所需要的包 -->
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
  
  <!-- 运行该程序包中的代码所需的程序包 -->
  <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>

3 CMakeLists.txt文件介绍及配置

我们以功能包demo01_helloworld_vs下的CMakeLists.txt文件为例介绍CMakeLists.txt文件格式及配置

cmake_minimum_required(VERSION 3.0.2) #所需 cmake 版本
project(demo01_helloworld_vs) #功能包名称，会被 ${PROJECT_NAME} 的方式调用

## 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
# 设置构建所需要的软件包
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
)

## System dependencies are found with CMake's conventions
# 默认添加系统依赖
# 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
# 启动 python 模块支持
# 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 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
## 配置 msg 源文件
# add_message_files(
#   FILES
#   Message1.msg
#   Message2.msg
# )

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

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

## Generate added messages and services with any dependencies listed here
# 生成消息、服务时的依赖包
# generate_messages(
#   DEPENDENCIES
#   std_msgs
# )

################################################
## Declare ROS dynamic reconfigure parameters ##
## 声明 ROS 动态参数配置 ##
################################################

## 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 特定配置##
###################################
## 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
# 运行时依赖
catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES demo01_helloworld_vs
#  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
# 添加头文件路径，当前程序包的头文件路径位于其他文件路径之前
include_directories(
# include
  ${catkin_INCLUDE_DIRS}
)

## Declare a C++ library
# 声明 C++ 库
# add_library(${PROJECT_NAME}
#   src/${PROJECT_NAME}/demo01_helloworld_vs.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
# 添加库的 cmake 目标依赖
# 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
# 声明 C++ 可执行文件
# add_executable(${PROJECT_NAME}_node src/demo01_helloworld_vs_node.cpp)
  add_executable(helloworld_vs_c src/helloworld_vs_c.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"
# 重命名c++可执行文件
# set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX "")

## Add cmake target dependencies of the executable
## same as for the library above
# 添加可执行文件的 cmake 目标依赖
# add_dependencies(${PROJECT_NAME}_node ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
  add_dependencies(helloworld_vs_c ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})

## Specify libraries to link a library or executable target against
# 指定库、可执行文件的链接库
# target_link_libraries(${PROJECT_NAME}_node
#   ${catkin_LIBRARIES}
# )
 target_link_libraries(helloworld_vs_c
   ${catkin_LIBRARIES}
 )

#############
## Install ##
## 安装 ##
#############

# 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
# 设置用于安装的可执行脚本
# catkin_install_python(PROGRAMS
#   scripts/my_python_script
#   DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
# )
catkin_install_python(PROGRAMS
  scripts/helloworld_vs_p.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_helloworld_vs.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)

launch文件的编写及ROS配置文件介绍到此就更新完毕，创作不易，希望大家多多点赞收藏，感谢大家！！！

---

参考资料：
http://www.autolabor.com.cn/book/ROSTutorials/
http://events.jianshu.io/p/0450e74cbe4a