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Description

As an independent task, let's create a package named my_launch_pkg, in which a run_transforms_and_markers.launch.py will start the following:

  • A node that publishes the map, orbit1, and orbit2 frames (ros2 run arj_transforms_cpp pub_transforms)
  • The rqt_reconfigure (ros2 run rqt_reconfigure rqt_reconfigure)
  • The static orbit3 frame (ros2 run tf2_ros static_transform_publisher --x 1.0 --y 0.2 --z 1.4 --qx 0.0 --qy 0.0 --qz 0.0 --qw 1.0 --frame-id orbit2 --child-frame-id orbit3)
  • And the launch that starts Rviz2 (ros2 launch arj_transforms_cpp rviz1.launch.py)

Verify the correct operation in rviz2.

So, at the end of the independent task, it should be possible to start it with the following command:

ros2 launch my_launch_pkg run_transforms_and_markers.launch.py

Create the my_launch_pkg package

Prerequisite: the arj_transforms_cpp package must already be built and runnable.

If the my_launch_pkg package already exists, delete it. (In the lab, it is possible that someone created it in the previous semester.)

cd ~ && test -d "ros2_ws/src/my_launch_pkg" && echo Exists || echo Does not exist

rm -r ~/ros2_ws/src/my_launch_pkg

Open a new terminal and source the installation (if not in bashrc), so that the ros2 commands work.

Navigate to the already created ros2_ws directory.

It is important to create the packages in the src directory, not in the root of the workspace. So navigate to the ros2_ws/src folder and run the package creation command:

cd ~/ros2_ws/src

ros2 pkg create --build-type ament_cmake my_launch_pkg

The terminal will return a message confirming the creation of the my_launch_pkg package and all necessary files and folders.

Launch folder

Create a folder for the launch files:

cd ~/ros2_ws/src/my_launch_pkg

mkdir launch

Create the launch file

cd launch

code run_transforms_and_markers.launch.py

Compose a launch file:

from launch import LaunchDescription
from launch_ros.actions import Node
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch_ros.substitutions import FindPackageShare


def generate_launch_description():
    return LaunchDescription([
        # ros2 run arj_transforms_cpp pub_transforms
        Node(
            package='arj_transforms_cpp',
            executable='pub_transforms',
        ),
        # ros2 run rqt_reconfigure rqt_reconfigure
        Node(
            package='rqt_reconfigure',
            executable='rqt_reconfigure',
        ),
        # ros2 run tf2_ros static_transform_publisher --x 1.0 --y 0.2 --z 1.4 --qx 0.0 --qy 0.0 --qz 0.0 --qw 1.0 --frame-id orbit2 --child-frame-id orbit3
        Node(
            package='tf2_ros',
            executable='static_transform_publisher',
            arguments=['1.0', '0.2', '1.4','0', '0', '0', '1', 'orbit2','orbit3'],
        ),     
        # ros2 launch arj_transforms_cpp rviz1.launch.py
        IncludeLaunchDescription(
            PythonLaunchDescriptionSource([
                FindPackageShare("arj_transforms_cpp"), '/launch/', 'rviz1.launch.py'])
        ),
    ])

Using ROS2 launch

The created launch file can be started as follows:

cd ~/ros2_ws/src/my_launch_pkg/launch # enter the folder containing the launch file

ros2 launch run_transforms_and_markers.launch.py

In addition to the direct method shown above, a launch file can also be run by the package:

ros2 launch <package_name> <launch_file_name>

For packages that contain launch files, it is advisable to create an exec_depend dependency on the ros2launch package in the package's package.xml file:

<exec_depend>ros2launch</exec_depend>

This ensures that the ros2 launch command is available after the package is built.

Add to the package to be runnable from anywhere

cd ~/ros2_ws/src/my_launch_pkg

code .

Insert the following line before <test_depend> in the package.xml:

<exec_depend>ros2launch</exec_depend>

Insert the following 2 lines before ament_package() in the CMakeLists.txt:

install(DIRECTORY launch
  DESTINATION share/${PROJECT_NAME})

Build in the usual way:

cd ~/ros2_ws

colcon build --packages-select my_launch_pkg

source ~/ros2_ws/install/setup.bash

This command can now be issued from anywhere:

ros2 launch my_launch_pkg run_transforms_and_markers.launch.py

Sources