4. Chapter 4a: ROS Actions #Part 1

4a.1 Playing with the Quadrotor simulation

• rostopic pub /drone/takeoff std_msgs/Empty "{}"

• rosrun teleop_twist_keyboard teleop_twist_keyboard.py

• rostopic pub /drone/land std_msgs/Empty "{}"

4a.2 What are ROS Actions

• Actions are like asynchronous call to service

• Actions are the same as services.

• When you call an action, you are calling a functionality that another node is providing.

• The difference is that when your node calls a service, it must wail the service finished.

  • WHen your node calls an action, it doesn't necessarily have to wait for the action to complete.

• Hence, an action is an asynchronous call to another node's functionality

  • The node that provides the functionality has to contain an action server. The action server allows other nodes to call that action functionality.

  • The node that calls to the functionality has to contain an action client. The action clien allow a node to connect to the action server to another node

    

• 서비스의 리스트를 볼때는 rosservice list

• 액션의 리스트를 볼때는 rosaction list 가 아니라 rostopic list

• top과 action을 어떻게 비교 하나? 일반적으로 아래의 5가지 액션 topic만 쓰는 구조이므로 이걸로 기억 하기

  • /{}_action_server/cancel
  • /{}_action_server/feedback
  • /{}_action_server/goal
  • /{}_action_server/result
  • /{}_action_server/status

4a.3 Calling an Action Server

• calling an action server mean sending a message to it

• In the same way as with topics and services, it all works by passing messages around

  • The message of topic is composed of a single part : the inforatmion the topic provides
  • The message of a service has tow part : the goal and the response
  • The message of an action serviver is devided in tree part : the goal, the result, and the feedback.

• All of the action messages used are defined in the action directory of their package

  • 해당 package에 가면 action이란 폴더가 있음. 해당 폴더 안에 {}.action이란 파일 존재

• goal : COnsist of variable called nseconds of type int32.

  • This int32 type is a standard ROS message, therefore, it can be foun in the std_msgs_package
  • Because it's a standard package of ROS, it's net needed to indicate the package where the int32 can be found

• Result : Consis of a variable called allPictures, an array of type CompressedImages[] found in the sensor_msgs_package

• feedback : consist of a variable called lastImage of type CompressedImages[] found in the sensor_msgs_package

  • The feedback is a message that the action server generates every once in a while to indicate how the action is going

[정리] How to call an action server

• The way you call an action server is by implementing an action client

코드설명

4a.4 Performing other tasks while the Action is in progress

• The simpleActionClient objects have two functions that can be used for knowing if the action that is being performed has finished, and how:
  • wait_for_result()
  • get_state() : pending(0), active(1), done(2), warn(3), error(4), 2보다 낮으면 아직 작업중이므로...

[코드] wait_for_result()

[코드] get_state()

4a.5 The axclient

• 지금까지의 아래의 두 방법을 이용하여서 action server에 goal을 전송 하였다.

  • Publishing directly into the /goal topic of the Action Server
  • Publishing the goal unsing Python code

• 좀더 편하고 쉬운 방법이 있다. axclient

  • The axclient is a GUI tool provided by the actionlib packages
  • that allows you to interact with an Action Server in a easy/Visual way
  • 실행법 rosrun actionlib axclient.py /ardrone_action_server

4. Chapter 4b: ROS Actions #Part 2

4b.1 Writing an Action Server

• Directly

#goal의 type 정보 읽어 오기 
rostopic info /fibonacci_as/goal

# pub로 실행
rostopic pub /fibonacci_as/goal actionlib_tutorials/FibonacciActionGoal "header" TAB + TAB`하여 전체 내용 출력 되면 값 수정 

# 값의 type은 src/..../action폴더의 *.action파일로 확인 가능

• python코드로 실행

코드설명

4b.2 Creating your own Action Server Message

4b.3 Custom Action Messages compilation