ROS Learning Notes

ROS Learning Notes 11

Keypoints

• Launch file syntax
• Examples

launch file syntax

• launch file is a xml file that can launch multiple nodes at the same time.
• launch file can start ros master automatically.
• Example:

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

  • pkg is the package name
  • type is the node name
  • name is the name when the node is launched
  • output is the output type of the node to the terminal
  • respawn is to restart the node when it is killed
  • required is to kill all the nodes when one of them is killed
  • ns is to add a namespace to the node
  • args is to add arguments to the node
• Parameter:
  • <param> is to set the parameter of one node. Stored in ROS server.
  • <rosparam> is to set the parameter of multiple nodes. Stored in ROS server.
    • <param name="output_frame" value="odom"/>
      • name: parameter name
      • value: parameter value
    • <rosparam file="$(find my_package)/config/my_params.yaml" command="load" ns="params"/>
      • file: the path of the parameter file
      • command: the command to load the parameter file
        • load: load the parameter file
        • dump: dump the parameter file
        • delete: delete the parameter file
      • ns: the namespace of the parameter file
  • arg is to set the argument of the launch file, only used in this launch file.
    • <arg name="output_frame" default="arg-value"/>
      • name: argument name
      • default: argument value
    • call the argument in the launch file:
      • <param name="output_frame" value="$(arg output_frame)"/> value must begin with $(arg. This value is decided by default in <arg>
      • <node name="node" pkg="package" type="type" output="screen" respawn="true" required="true" ns="namespace" args="$(arg output_frame)"/>
• <remap> is to remap the ROS computation graph resource. Just to rename the topic name.
  • <remap from="old_topic" to="new_topic"/>
    • from: the old topic name
    • to: the new topic name
• <include> is to include another launch file, like C language.
  • <include file="$(find my_package)/launch/my_launch_file.launch"/>
    • file: the path of the launch file

Examples

• simple launch file

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

• 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="turtle1"/>
            <param name="turtle_name2" value="turtle2"/>
            <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>
  

• start_tf_demo_c++.launch

    <launch>
        <!-- Tuetlesim Node -->
        <node pkg="turtlesim" type="turtlesim_node" name="turtlesim_node"/>
        <node pkg="turtlesim" type="turtle_teleop_key" name="turtle_teleop_key" 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="turtle_tf_listener"/>
    </launch>
  

• start_tf_demo_python.launch

    <launch>
        <!-- Tuetlesim Node -->
        <node pkg="turtlesim" type="turtlesim_node" name="turtlesim_node"/>
        <node pkg="turtlesim" type="turtle_teleop_key" name="turtle_teleop_key" output="screen"/>
  
        <node name="turtle1_tf_broadcaster" pkg="learning_tf" type="turtle_tf_broadcaster.py" >
            <param name="turtle" type="string" value="turtle1"/>
        </node>
  
        <node name="turtle2_tf_broadcaster" pkg="learning_tf" type="turtle_tf_broadcaster.py" >
            <param name="turtle" type="string" value="turtle2"/>
        </node>
  
        <node pkg="learning_tf" type="turtle_tf_listener.py" name="turtle_tf_listener"/>
  
    </launch>
  

• 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>
  

---