Version: ROS2 Foxy

Platform: Ubuntu 20:04

Hello everyone,

I'm programmatically calling a launch file 'c' from a launch file 'b' from a launch file 'a' which is called in the terminal. In launch file 'b' I have two hard coded variables to calculate how many robots I want to spawn and where to spawn them. I want these hard coded variables to become arguments which are passed to launch file 'b' from launch file 'a'.

Without over complicating the question, I need to be able to perform calculations using them as typical python variables.

import os
from ament_index_python.packages import get_package_share_directory, get_package_prefix
from launch import LaunchDescription, LaunchContext
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch.substitutions import TextSubstitution, LaunchConfiguration,PythonExpression,PathJoinSubstitution

def gen_robot_list(number_of_robots, map_number):

#This function will calculate robot attributes using two variables
#This is the one condition I dont want to have to change.
_ = ''


def generate_launch_description():

#Process the URDF file
pkg_path = os.path.join(get_package_share_directory('my_bot'))
xacro_file = os.path.join(pkg_path,'description','robot.urdf.xacro')

map_number = LaunchConfiguration('map_number')
number_of_robots = LaunchConfiguration('number_of_robots')

#Below is where the argument variables will go (Replacing '2' and '7')
robots = gen_robot_list(2, 7)

# Create the list of spawn robots commands
spawn_robots_cmds = []

# Below is all neccessary for multi-robot control within ros name spaces and stuff
for robot in robots:
    print("#############"+str(robot))
    spawn_robots_cmds.append(
        IncludeLaunchDescription(
            PythonLaunchDescriptionSource(os.path.join(
                get_package_share_directory('my_bot'), 'launch', 'c.launch.py')),
            # Arguments to pass into the node which spawns the robot entity in gazebo
            launch_arguments={
                              'robot_urdf': xacro_file,
                              'x': TextSubstitution(text=str(robot['x_pose'])),
                              'y': TextSubstitution(text=str(robot['y_pose'])),
                              'z': TextSubstitution(text=str(robot['z_pose'])),
                              'robot_name': robot['name'],
                              'robot_name_prefix': robot['name']+'/',
                              'robot_namespace': robot['ns'],
                              'use_sim_time': 'true',
                              'rotation': TextSubstitution(text=str(robot['rotation'])),
                              }.items()
        )
    )

# Create the launch description and populate
ld = LaunchDescription()
# Creates a independent launch desc for each robot in list creating
# multiple robot state publishers and entity spawners
for spawn_robot_cmd in spawn_robots_cmds:
    ld.add_action(spawn_robot_cmd)

return ld

What have I tried so far:

I have managed to add simple LaunchArguments that I convert to LaunchConfiguration's. `

Declare a launch argument 'map_number'

map_number_arg = DeclareLaunchArgument(
    'map_number',
    default_value='1',
    description='Number of the map to be launched'
)

robot_number_arg = DeclareLaunchArgument(
    'robot_numbers',
    default_value='3',
    description='Number of robots to be launched'
)

# This Launch file handles the simulation of the environment (Gazebo)
start_world = IncludeLaunchDescription(
    PythonLaunchDescriptionSource(os.path.join(get_package_share_directory(package_name), 'launch', 'start_world.launch.py')),
    launch_arguments={
        'map_number': LaunchConfiguration('map_number'),
        'robot_number': TextSubstitution(text=str(LaunchConfiguration('robot_number')))
    }.items()
)`

These launch configuration can be passed to different launch files fine. But I cant access them as normal python variables I.E. I cant do LC=LaunchConfiguration('number_of_robots') then for i in range of(LC): or if LC==1:

I tried using Opaque Functions which allows the perform(context) function to work. This was the closest solution so far but I'm pretty sure they can only be used to launch nodes, not deal with calling other Launch files. I think this because every source code I have found using OpaqueFunction directly calls a ... (more)