launch文件：通过XML文件实现多节点的配置和启动（可自动启动ROS Master)
launch文件中包含很多标签和属性
*launch文件语法
<launch>
<node pkg="turtlesim" name = "sim1" type="turtlesim_nade"/>
<node pkg="turtlesim" name = "sim2" type="turtlesim_node"/>
</launch>
<launch> launch文件中的根元素采用<launch>标签定义
启动节点
<node pkg="package-name"type="executable-name"name="node-name"/>
* pkg: 节点所在的功能包名称
<node> * type:节点的可执行文件名称
* name: 节点运行时的名称
* output 、respawn、required 、ns 、args
参数设置
<paran>/
<rosparam>
设置ROS系统运行中的参数，存储在参数服务器中
<param name="output_frame"value="odom"/>
*name:参数名
*value:参数值
加载参数文件中的多个参数
<rosparam file="params.yaml" command="load" ns= "params"/>
<arg>
launch文件内部的局部变量，仅限于launch文件使用
<arg name="arg-name" default="arg-value"/>
* name: 参数名
* value: 参数值 调用如下
<param name="foo" value="$(arg arg-value"/>
<node name="node" pkg="package"type="type" args="$(arg arg-name)"/>
重映射
标签<remap>
重映射RoS计算图资源的命名
<remap from="/turtlebot/cmd_vel"to="/cmd_vel"/>
*from :原命名
* to : 映射之后的命名
嵌套
<include>
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 :包含的其他launch文件路径
我习惯的在src目录下创建对应的功能包，为了更好的管理代码空间
$ cd ~/catkin_ws/src
$ catkin_create_pkg learning_launch
下面介绍一些launch文件的应用例子
例１：simple.launch
1 <launch>
2 <node pkg="learning_topic" type="person_subscriber" name="talk er" output="screen" />
3 <node pkg="learning_topic" type="person_publisher" name="liste ner" output="screen" />
4 </launch>
这个launch文件比较简单，用一个根标签包含两个node标签，启动两个node节点，启动launch文件如下，观察到两个节点并行运行。而且不需要再去启动roscore,已经自动启动了。
qqtsj ~ roslaunch learning_launch simple.launch
... logging to /home/qqtsj/.ros/log/a8e85210-44bd-11ea-aa0f-9822efa1466f/roslaunch-qqtsj-Nitro-AN515-51-21388.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB. started roslaunch server http://qqtsj-Nitro-AN515-51:35961/ SUMMARY
======== PARAMETERS
* /rosdistro: melodic
* /rosversion: 1.14.3 NODES
/
listener (learning_topic/person_publisher)
talker (learning_topic/person_subscriber) auto-starting new master
process[master]: started with pid [21398]
ROS_MASTER_URI=http://localhost:11311 setting /run_id to a8e85210-44bd-11ea-aa0f-9822efa1466f
process[rosout-1]: started with pid [21409]
started core service [/rosout]
process[talker-2]: started with pid [21412]
process[listener-3]: started with pid [21414]
[ INFO] [1580539196.883750317]: Publish Person Info: name:Tom age:18 sex:1
[ INFO] [1580539197.883984881]: Publish Person Info: name:Tom age:18 sex:1
[ INFO] [1580539197.884465911]: Subcribe Person Info: name:Tom age:18 sex:1
[ INFO] [1580539198.883864113]: Publish Person Info: name:Tom age:18 sex:1
[ INFO] [1580539198.884350887]: Subcribe Person Info: name:Tom age:18 sex:1
例２: turtlesim_parameter_config.launch
1 <launch>
2
3 <param name="/turtle_number" value="2"/>
4
5 <node pkg="turtlesim" type="turtlesim_node" name="turtlesim_no de">
6 <param name="turtle_name1" value="Tom"/>
7 <param name="turtle_name2" value="Jerry"/>
8
9 <rosparam file="$(find learning_launch)/config/param.yaml" command="load"/>
10 </node>
11
12 <node pkg="turtlesim" type="turtle_teleop_key" name="turtle_te leop_key" output="screen"/>
13
14 </launch>
15
16
这个launch文件用于参数设置
qqtsj ~ roslaunch learning_launch turtlesim_parameter_config.launch
... logging to /home/qqtsj/.ros/log/fffc0146-44c2-11ea-aa0f-9822efa1466f/roslaunch-qqtsj-Nitro-AN515-51-23633.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB. started roslaunch server http://qqtsj-Nitro-AN515-51:36955/ SUMMARY
======== PARAMETERS
* /rosdistro: melodic
* /rosversion: 1.14.3
* /turtle_number: 2
* /turtlesim_node/A: 123
* /turtlesim_node/B: hello
* /turtlesim_node/group/C: 456
* /turtlesim_node/group/D: hello
* /turtlesim_node/turtle_name1: Tom
* /turtlesim_node/turtle_name2: Jerry NODES
/
turtle_teleop_key (turtlesim/turtle_teleop_key)
turtlesim_node (turtlesim/turtlesim_node) auto-starting new master
process[master]: started with pid [23643]
ROS_MASTER_URI=http://localhost:11311 setting /run_id to fffc0146-44c2-11ea-aa0f-9822efa1466f
process[rosout-1]: started with pid [23654]
started core service [/rosout]
process[turtlesim_node-2]: started with pid [23661]
process[turtle_teleop_key-3]: started with pid [23662]
Reading from keyboard
---------------------------
Use arrow keys to move the turtle.
qqtsj ~ rosparam list
/background_b
/background_g
/background_r
/rosdistro
/roslaunch/uris/host_qqtsj_nitro_an515_51__36955
/rosversion
/run_id
/turtle_number
/turtlesim_node/A
/turtlesim_node/B
/turtlesim_node/group/C
/turtlesim_node/group/D
/turtlesim_node/turtle_name1
/turtlesim_node/turtle_name2
例３：start_tf_demo_c++.launch
1 <launch>
2
3 <!-- Turtlesim Node-->
4 <node pkg="turtlesim" type="turtlesim_node" name="sim"/>
5 <node pkg="turtlesim" type="turtle_teleop_key" name="teleop" o utput="screen"/>
6
7 <node pkg="learning_tf" type="turtle_tf_broadcaster" args="/tu rtle1" name="turtle1_tf_broadcaster" />
8 <node pkg="learning_tf" type="turtle_tf_broadcaster" args="/tu rtle2" name="turtle2_tf_broadcaster" />
9
10 <node pkg="learning_tf" type="turtle_tf_listener" name="listen er" />
11
12 </launch>
这个launch文件是上讲说的小海龟跟随实例，这里不需要开启５个终端，只需要运行对应的launch文件就可以了
qqtsj ~ roslaunch learning_launch start_tf_demo_c++.launch
... logging to /home/qqtsj/.ros/log/bb367d92-44cd-11ea-aa0f-9822efa1466f/roslaunch-qqtsj-Nitro-AN515-51-25949.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB. started roslaunch server http://qqtsj-Nitro-AN515-51:39467/ SUMMARY
======== PARAMETERS
* /rosdistro: melodic
* /rosversion: 1.14.3 NODES
/
listener (learning_tf/turtle_tf_listener)
sim (turtlesim/turtlesim_node)
teleop (turtlesim/turtle_teleop_key)
turtle1_tf_broadcaster (learning_tf/turtle_tf_broadcaster)
turtle2_tf_broadcaster (learning_tf/turtle_tf_broadcaster) auto-starting new master
process[master]: started with pid [25959]
ROS_MASTER_URI=http://localhost:11311 setting /run_id to bb367d92-44cd-11ea-aa0f-9822efa1466f
process[rosout-1]: started with pid [25970]
started core service [/rosout]
process[sim-2]: started with pid [25973]
process[teleop-3]: started with pid [25977]
process[turtle1_tf_broadcaster-4]: started with pid [25979]
Reading from keyboard
---------------------------
Use arrow keys to move the turtle.
process[turtle2_tf_broadcaster-5]: started with pid [25981]
process[listener-6]: started with pid [25987]