from turtlesim Study ROS2 Parameters

Preface

Study ROS2 Way , Not through learning ROS1 Instead of , because ROS2 Of “ kernel ” differ ROS1, We must seriously start from scratch and learn again .

Ubuntu edition ：20.04

ROS edition ：Foxy

Review of study notes

• ROS2 Learning notes ( One ) Get document
• ubuntu20.04 install ROS2 and ROS1 coexistence
• ROS2 Learning notes ( Two ) from turtlesim Study ROS2 node
• ROS2 Learning notes ( 3、 ... and ) from turtlesim Study ROS2 The theme
• ROS2 Learning notes ( Four ) from turtlesim Study ROS2 service

1.ROS2 param

Whether it's ROS1 still ROS2, Parameters are very important knowledge points , It is mainly the configuration of node functions , stay ROS2 Each node in the has its own parameters .

2. Start the little turtle simulator first

$ ros2 run turtlesim turtlesim_node
$ ros2 run turtlesim turtle_teleop_key

3.ros2 param list

This command can be used to view all parameters of the current node , Enter the following command in the new terminal ：

$ ros2 param list
----
/teleop_turtle:
  qos_overrides./parameter_events.publisher.depth
  qos_overrides./parameter_events.publisher.durability
  qos_overrides./parameter_events.publisher.history
  qos_overrides./parameter_events.publisher.reliability
  scale_angular
  scale_linear
  use_sim_time
/turtlesim:
  background_b
  background_g
  background_r
  qos_overrides./parameter_events.publisher.depth
  qos_overrides./parameter_events.publisher.durability
  qos_overrides./parameter_events.publisher.history
  qos_overrides./parameter_events.publisher.reliability
  use_sim_time

Because we opened two nodes , So you can see the nodes /teleop_turtle and /turtlesim, This is followed by all parameters of each node .

Every node has use_sim_time Parameters .

4.ros2 param get

This command can get the type and current value of the parameter , Command format ：

$ ros2 param get <node_name> <parameter_name>

We get background_g Parameter to get the green value in the background color .

$ ros2 param get /turtlesim background_g
----
Integer value is: 86

You can see that the type returned is an integer , The value is 86.
Of course , obtain background_r and background_b It's all the same .

5.ros2 param set

The change command can change the running parameters , The command format is as follows ：

$ ros2 param set <node_name> <parameter_name> <value>

At this time , We can try to change the background color of the little turtle simulator red Value ：

$ ros2 param set /turtlesim background_r 150
----
Set parameter successful

Return to see successful Description parameter setting succeeded , The effect is as follows ：

set The command does not permanently change parameter values , Can only be saved in the current process .

6.ros2 param dump

This command can save the parameters and reload the saved parameters after starting the node next time , The command format is as follows ：

$ ros2 param dump <node_name>

Try to save the settings above /turtlesim Background color parameters , The command is as follows :

$ ros2 param dump /turtlesim
----
Saving to:  ./turtlesim.yaml

The configuration file will be saved to the current running directory , Double click to open view , The contents of the document are as follows ：

/turtlesim:
  ros__parameters:
    background_b: 255
    background_g: 86
    background_r: 150
    use_sim_time: false

7. Load parameter file

You can use the following command format to load the parameter file into the currently running node ：

$ ros2 param load <node_name> <parameter_file>

take ./turtlesim.yaml Add to /turtlesim Go to the node , Use the following command ：

$ ros2 param load /turtlesim ./turtlesim.yaml
----
Set parameter background_b successful
Set parameter background_g successful
Set parameter background_r successful
Set parameter use_sim_time successful

After successful startup , The background as like as two peas and the same color as manually modified on the simulator are then available. .

summary

This is it. ROS2 Parameters in , We can use the command line get or set Parameter values , You can also use files to save and load parameters .

Reference:

https://docs.ros.org/en/foxy/Tutorials/Parameters/Understanding-ROS2-Parameters.html

Conclusion

This paper is also based on the author's learning and use experience , Strong subjectivity , If there is anything wrong or unclear , Welcome to leave a message in the comments area ~

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