前言

使用命令行输入代码需要不断打开终端比较繁琐，而且容易输入错误，那么有没有什么方法可以快速启动所需节点呢？

一、launch文件介绍

Launch文件：通过XML文件实现多节点的配置和启动（可自启动ROS Master）
命令行语法：

roslaunch 功能包名 launch文件名

二、Launch文件常用核心语法

<launch>
		<node pkg = "turtlesim" name="sim1" type="turtlesim_node" />
		<node pkg = "turtlesim" name="sim2" type="turtlesim_node" />
</launch>

注：launch文件以< launch >开始，结束

1.< node >语法

<node pkg = "package-name" type = "executable-name" name= "node-name"/>

2.参数设置

（1）< param >/< rosparam >

< param >设置ROS系统运行中的参数，存储在参数服务其中。

<param name = "output_frame" value="odem" />

• name：参数名
• value：参数值

< rosparam > 加载参数文件中的多个参数：

<rosparam file="params.yaml" command="load" ns="params" />

其中，ns是命名空间(name space)

（2）< arg >

< arg > launch文件内部的局部变量，仅限于launch文件使用

设置参数

<arg name="arg-name" value="arg-value" />

• name：参数名
• value：参数值

参数调用:

<param name="foo" value="$(arg arg-name)" />
<node name="node" pkg="package" type="type" args="$(arg arg-name)" />

3.重映射

< remap >重映射ROS计算机资源的命名

<remap from="/turtlebot/cmd_vel" to="/cmd_vel"/>

• from：原命名
• to：映射之后的命名

4.嵌套

< include >内嵌包含其他launch文件，类似C语言中的头文件包含。

<include file="$(dirname)/other.launch" />

• file:包含其他launch文件路径

三、launch案例

1. 创建功能包

cd ~/catkin_ws/src
catkin_create_pkg learning_launch
cd learning_launch
mkdir launch

注：launch功能包不需要依赖包

2.simple.launch

cd ~/catkin_ws/src/learning_launch/launch
touch simple.launch
gedit simple.launch

<launch>
	<node pkg="learning_topic" type="person_subscriber" name="talker" output="screen" />
	<node pkg="learning_topic" type="person_publisher" name="listener" output="screen" />
</launch>

注：启动的节点所在功能包和可执行文件（.cpp文件）的创建请参考：ROS学习（四）–1.发布者与订阅者案例

编译：

cd ~/catkin_ws
catkin_make

运行：

source ~/catkin_ws/devel/setup.bash
roslaunch learning_launch simple.launch

由图可知，launch启动节点成功！

3.turtlesim_parameter_config.launch

cd ~/catkin_ws/src/learning_launch/launch
touch turtlesim_parameter_config.launch
gedit turtlesim_parameter_config.launch

<launch>
	<param name="/turtle_number" value="2" />
	<node pkg="turtlesim" type="turtlesim_node" name="turtlesim_node" >
		<param name="turtle_name1" value="Tom" />
		<param name="turtle_name2" value="Jerry" />
		<rosparam file="$(find learning_launch)/config/param.yaml" command="load" />
	</node>
	<node pkg="turtlesim" type="turtle_teleop_key" name="turtle_teleop_key" output="screen" />
</launch>

注：1.find learning_launch：自动寻找learning_launch路径

编译：

cd ~/catkin_ws
catkin_make

注：运行前需要先添加config/param.yaml文件

cd ~/catkin_ws/src/learning_launch
mkdir config
cd config
touch param.yaml
gedit param.yaml

A: 123
B: "hello"

group:
  C: 456
  D: "hello"

运行：

source ~/catkin_ws/devel/setup.bash
roslaunch learning_launch turtlesim_parameter_config.launch

由图可知，launch文件启动海龟仿真器和海龟移动控制器成功。同时launch文件参数设置和加载param.yaml文件参数成功

4.start_tf_demo_c++.launch

cd ~/catkin_ws/src/learning_launch/launch
touch start_tf_demo_c++.launch
gedit start_tf_demo_c++.launch

<launch>
	<node pkg="turtlesim" type="turtlesim_node" name="sim" />
	<node pkg="turtlesim" type="turtle_teleop_key" name="teleop" output="screen" />

	<node pkg="learning_tf" type="turtle_tf_broadcaster" args="/turtle1" name="turtle1_tf_broadcaster" />
	<node pkg="learning_tf" type="turtle_tf_broadcaster" args="/turtle2" name="turtle2_tf_broadcaster" />
	<node pkg="learning_tf" type="turtle_tf_listener" name="listener" />
</launch>

注：启动的节点所在功能包和可执行文件（.cpp文件）的创建请参考：ROS学习（七）坐标系管理系统
编译：

cd ~/catkin_ws
catkin_make

运行：

source ~/catkin_ws/devel/setup.bash
roslaunch learning_launch start_tf_demo_c++.launch

5.turtlesim_remap.launch

cd ~/catkin_ws/src/learning_launch/launch
touch turtlesim_remap.launch
gedit turtlesim_remap.launch

<launch>
	<include file="$(find learning_launch)/launch/simple.launch" />

	<node pkg="turtlesim" type="turtlesim_node" name="turtlesim_node">
		<remap from="/turtle1/cmd_vel" to="/cmd_vel" />
	</node>
</launch>

编译：

cd ~/catkin_ws
catkin_make

运行：

source ~/catkin_ws/devel/setup.bash
roslaunch learning_launch turtlesim_remap.launch

由图可知，simple.launch文件包含成功，同时remap重命名成功，成功将”/turtle1/cmd_vel”重命名为”/cmd_vel” ，向”/cmd_vel” 发布话题，海龟成功移动，说明重命名成功