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How to auto-build & setup ROS package in sub-directory from launch file

This example shows how to colcon build (if neccessary) a ROS package in a sub-directory, and add it to the AMENT_PREFIX_PATH for the current launch.

In this example, we’ll use franka_description as the package to be built:

Library file: ros_autobuild.py:

import subprocess
import os.path

def autobuild_and_setup_ros_package(package_name, package_path):
    # If [package]/install does not exist, run colcon_build there
    install_path = os.path.join(package_path, "install")
    if not os.path.exists(os.path.join(package_path, "install")):
        print(
            f"{package_path}/install does not exist. Running 'colcon build' in {package_path}"
        )
        subprocess.run(["colcon", "build"], cwd=package_path)
    # Preprend absolute path of [package]/install/[package] to AMENT_PREFIX_PATH
    extra_path = os.path.abspath(os.path.join(install_path, package_name))
    os.environ["AMENT_PREFIX_PATH"] = extra_path + os.pathsep + os.environ.get("AMENT_PREFIX_PATH", "")

In your launch file, here’s how to use it:

import ros_autobuild

def generate_launch_description():
  ros_autobuild.autobuild_and_setup_ros_package(
    "franka_description",
    # Example: franka_description folder in the same directory
    os.path.join(os.path.dirname(__file__), "franka_description")
  )
  # [...] The rest of your launch file