古月老师ROS入门21讲笔记。

.launch启动文件：语法结构是XML，包含多种节点的配置和启动。可以自动启动ROS Master并且避免了多次不断打开终端，不断输入指令的麻烦。

语法

1.必须包含根元素< launch> 和 < /launch>，放在开头和结尾。

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

2.启动节点：< node>

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

pkg: 节点所在的功能包名称
type: 节点的可执行文件名称
name: 节点运行时的名称，节点名字取代掉程序运行初始化的名字。
output 、respawn 、 required 、ns 、 args
3.储存在参数服务器中，参数设置 < param > / < rosparam>，设置ROS系统运行中的参数。
存储一个参数时：name: 参数名，value: 参数值

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

如果要加载参数文件中的多个参数：

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

4.存在launch文件内部的局部变量，仅限于launch文件的使用。也可以作为node的输入参数

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

也可以作为node的输入参数，调用arg-name:

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

5.重映射：重新命名ROS计算图资源 < remap>
from: 原命名
to: 映射之后的命名

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

6.嵌套：包含其他launch文件，类似C语言的头文件包含。< include>

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

另外可以参考wiki：链接

launch示例

1. simple.launch
   在learning_topic功能包下运行Publisher&Subscriber，把日志信息打印到终端中。

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

2.turtlesim_parameter_config.launch配置参数

<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>

3.start_tf_demo_c++.launch,海龟跟随案例

 <launch>
    <!-- Turtlesim Node-->
    <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>

4.turtlesim_remap.launch，remap&include案例。remap重命名指令，原命令资源消除。

<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>

编译并运行

$ catkin_make
$ roslaunch learning_launch simple.launch
$ roslaunch learning_launch turtlesim_parameter_config.launch
$ roslaunch learning_launch start_tf_demo_c++.launch
$ roslaunch learning_launch turtlesim_remap.launch

ps: ros资源整合时，会用.launch在做搭积木的过程。