ROS notes (10) - Launch file startup

1. background

Multiple nodes may need to be started in a program , such as :ROS Built in Little Turtle case , If you want to control tortoise movement , To start multiple windows , To start, respectively, roscore、 Tortoise interface node 、 Keyboard control node . If you call every time rosrun Start one by one , Obviously inefficient , How to optimize ?

The official optimization strategy is launch file （ adopt xml File to achieve multi node configuration and startup ）, You can start more than one at a time ROS node , And it can start automatically ROS Master.

2. Realization

2.1 Create Feature Pack

$ catkin_create_pkg launch 
Created file launch/package.xml
Created file launch/CMakeLists.txt
Successfully created files in /home/wohu/project/ros/ros_demo/src/launch. Please adjust the values in package.xml.

2.2 add to launch file

launch.yaml The contents of the document

<launch>
    <node pkg="turtlesim" type="turtlesim_node" name="t1"/>
    <node pkg="turtlesim" type="turtle_teleop_key" name="key1" />
</launch>

2.3 function

$ roslaunch launch  launch.yaml 
... logging to /home/wohu/.ros/log/e021148a-f125-11ec-92ca-00e070ce7d11/roslaunch-wohu-pc-17490.log
Checking log directory for disk usage. This may take a while.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://wohu-pc:35733/

SUMMARY
========

PARAMETERS
 * /rosdistro: melodic
 * /rosversion: 1.14.13

NODES
  /
    key1 (turtlesim/turtle_teleop_key)
    t1 (turtlesim/turtlesim_node)

auto-starting new master
process[master]: started with pid [17500]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to e021148a-f125-11ec-92ca-00e070ce7d11
process[rosout-1]: started with pid [17512]
started core service [/rosout]
process[t1-2]: started with pid [17516]
process[key1-3]: started with pid [17520]

3. launch File syntax

3.1 launch label

<launch> All labels are launch The root tag of the file , Act as a container for other labels , All other labels are launch The children of .

3.2 node label

<node> Labels are used to specify ROS node , Is the most common label , It should be noted that : roslaunch Orders do not guarantee compliance with node Start the node in the declared order ( The startup of nodes is multi process ).

Properties are as follows ：

• pkg=“ Package name ”

  The package to which the node belongs

• type=“nodeType”

  Node type ( An executable with the same name )

• name=“nodeName”

  The name of the node ( stay ROS The name of the node in the network topology )

• args=“xxx xxx xxx” ( Optional )

  Pass parameters to node

• machine=“ machine name ”

  Start the node on the specified machine

• respawn=“true | false” ( Optional )

  If the node exits , Whether to restart automatically

• respawn_delay=" N" ( Optional )

  If respawn by true, So delay N Start the node in seconds

• required=“true | false” ( Optional )

  Whether the node must , If true, Then, if the node exits , Will kill the whole roslaunch

• ns=“xxx” ( Optional )

  In the specified namespace xxx Start node

• clear_params=“true | false” ( Optional )

  Before starting , Delete all parameters of the node's private space

• output=“log | screen” ( Optional )

  Log sending destination , It can be set to log Log files , or screen The screen , The default is log

Child labels

• env Environment variable Settings

• remap Remap node name

• rosparam Parameter setting

• param Parameter setting

3.3 include label

include The tag is used to put another xml Format launch Import the file into the current file

attribute

• file=“$(find Package name )/xxx/xxx.launch”

  File path to include

• ns=“xxx” ( Optional )

  Import the file in the specified namespace

Child labels

• env Environment variable Settings

• arg Pass parameters to the included file

3.4 remap label

For topic renaming

• from=“xxx”
  Original topic name

• to=“yyy”
  Target name

3.5 param label

<param> The tag is mainly used to set parameters on the parameter server , The parameter source can be in the tag through value Appoint , It can also be loaded through external files , stay <node> In the label , Equivalent to private namespace .

attribute

• name=“ Namespace / Parameter name ”

  Parameter name , Can contain namespaces

• value=“xxx” ( Optional )

  Define parameter values , If omitted here , You must specify an external file as the parameter source

• type=“str | int | double | bool | yaml” ( Optional )

  Specify parameter type , If not specified ,roslaunch Will try to determine the parameter type , The following rules :

  If you include ‘.’ The number of is not parsed as a floating point type , Otherwise, it is an integer
  “true” and “false” yes bool value ( Case insensitive )
  Others are strings

3.6 rosparam label

<rosparam> Labels can be from YAML File import parameters , Or export parameters to YAML file , It can also be used to delete parameters ,<rosparam> Tag in <node> Label is treated as private .

attribute

• command=“load | dump | delete” ( Optional , Default load)

  load 、 Export or delete parameters

• file=“$(find xxxxx)/xxx/yyy…”

  Loaded or exported to yaml file

• param=“ Parameter name ”

• ns=“ Namespace ” ( Optional )

3.7 group label

<group> Tags can group nodes , have ns attribute , Nodes can belong to a namespace

attribute

• ns=“ The name space ” ( Optional )

• clear_params=“true | false” ( Optional )

  Before startup , Delete all parameters of the group namespace ( Use with caution … This function is dangerous )

Child labels

 except launch  Labels other than labels 

3.8 arg label

<arg> Tags are used to dynamically transfer parameters , It's like a function parameter , Can enhance launch Flexibility of documents .

attribute

• name=“ Parameter name ”

• default=“ The default value is ” ( Optional )

• value=“ The number ” ( Optional )

  You can't be with default Coexist

• doc=“ describe ”

  Parameter description

Example ：

• launch Implementation of file parameter passing Syntax ,hello.lcaunch

<launch>
    <arg name="xxx" />
    <param name="param" value="$(arg xxx)" />
</launch>

• Command line call launch The ginseng

roslaunch hello.launch xxx:= value