ipa-rar / ros2_practice_workspace

This repo contains all the ros2 packages created for understanding the core concepts of ros2-foxy

Some tips and notes for ros2 dummies

common

• Always add the nodes @entry_points of the setup.py

'node_name=pkg_name.file_name:ros2_function_name'

ros2_interface

• A pkg to add new msg, srv or act interfaces used in this stack.
• This pkg uses ament_cmake build system as there is currently no way to generate .msg and .srv file in a pure python package
• msg and srv should follow strictly SomeMsg.msg/SomeSrv.srv
• Add these to the package.xml as they rely on rosidl_default_generators for generating language-specific code.

  <!-- This is added to generate msgs nd srv -->
  <build_depend>rosidl_default_generators</build_depend>
  <exec_depend>rosidl_default_runtime</exec_depend>
  <member_of_group>rosidl_interface_packages</member_of_group>

• Add these lines to CMakeLists.txt to cnovert the interfaces you defined into language specific code.

# for generating msgs and srvs
find_package(rosidl_default_generators REQUIRED)
rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/MathsMsg.msg"
  "srv/MathsSrv.srv"
 )

ros2_pub & ros2_sub

• A pkg that publishes and subscribes MathsMsg over /maths_topic
• When using any msgs add them to the package.xml as <depend>msg_type</depend>
• To avoid error during a keyboard interrupt add an exception

rclpy.init('node_name)
try:
    _node_ = NodeName()
    rclpy.spin(_node_)

except KeyboardInterrupt:
    _node_.destroy_node()
    rclpy.shutdown()

- Create the node using py
- package.xml for adding dependencies
- setup.py for adding the pub and sub executable names

ros2_service_client & ros2_service_server

• A pkg to demo ros2 service client and server. Client sends requests and server responds back over MathsSrv service.
• The type and name of the service must match for the client and service to communicate.

ros2_launch

Launch files using python scripts

• Create a /launch folder inside the pkg create a *.py file

• Add this line to Setup.py so that colcon build can find it during the build process

    import os
    from glob import glob
    data_files=[
        ................................. ,
        ................................. ,
        (os.path.join('share', package_name), glob('launch/*.py'))
    ],

• Boilerplate code for launch_file.py

from launch import LaunchDescription
from launch_ros.actions import Node
    
    def generate_launch_description():
        ld = LaunchDescription()
        pub_node = Node(
            package="ros2_pub",
            executable="number_publisher"
        )
        sub_node = Node(
            package="ros2_pub",
            executable="number_subscriber"
        )

        ld.add_action(pub_node)
        ld.add_action(sub_node)

  return ld

launch files ref

Launch files using xml file

• Create a .xml file inside the /launch folder and use this as template.

<launch>
    <node pkg="ros2_pub" exec="number_publisher" output="screen"/>
    <node pkg="ros2_sub" exec="number_subscriber" output="screen"/>
</launch>

• To launch the nodes use

ros2 launch path/to/the/launch/file.xml

Resolving dependencies

•   rosdep install -i --from-path src --rosdistro foxy -y
  

Build pkgs

•   colcon build
  

• --symlink-install saves you from having to rebuild every time you tweak python scripts

• The install directory is where your workspace’s setup files are, which you can use to source your overlay.

• Source your underlay

• source /opt/ros/foxy/setup.bash  
  

• Source your overlay

•   . install/local_setup.bash
  

• Sourcing the local_setup of the overlay will only add the packages available in the overlay to your environment.

• setup sources the overlay as well as the underlay it was created in, allowing you to utilize both workspaces.

API rclpy

•   rcpy.create_node('node_name')
  

•   Node.create_publisher(publisher_handle,
                      msg_type
                      topic,
                      qos_profile)
  

•    publish(msg)
  

•   Node.creat_subscription(subscription_handle,
                            msg_type,
                            topic,
                            callback_function,
                            qos_profile  
                            )   
  

•   Node.create_service(service_handle,
                        srv_type,
                        srv_name,
                        qos_profile
                        )
  

•   send_response(response, header)
  

•   Node.create_client(cliet_handle,
    srv_type,
    srv_name,
    qos_profile)
  
    call(request)
    call_async(request)
  

•    wait_for_service(timeout_sec=None)
  

ros2_linting

ref to ament_linting

TODOS

• ros2_action_server and client
• ros2_lifecycle
• Passing arguments via launch files.
• parameters load and use