AIDDL External ROS2 Library

This library provides conversions between the AI Domain Definition Language (AIDDL) framework and ROS2. The main purpose of these converters is to be used in the aiddl_ros2_bridge ROS2 package (TODO: link) and ultimately decouple the AIDDL framework from ROS throught aiddl_external_grpc. ROS2 nodes from the aiddl_ros2_bridge can be configured to dynamically load converters. The overall envisioned usage of these packages is:

1. Install aiddl_external_ros2
2. Clone & build aiddl_ros2_bridge
3. Optional: write custom converters if needed (for custom ROS2 messages, services, or actions).

• Write a simple Python package with one class per message, service, or action and install it locally
• Use aiddl_external_ros2 to convert existing messages where possible (e.g., Pose, PoseStamped)

4. Write a YAML file describing ROS2 nodes and their AIDDL converters (from this package)
5. Launch all ROS2 nodes and control your robots through aiddl_external_grpc

Overview

Interaction with ROS2 comes in three flavors: messages, services and actions. For each of these we use different static methods.

Messages

Messages can be converted between AIDDL and ROS2 formats. The two methods for this are ros2aiddl and aiddl2ros. Thw following example shows how strings are converted.

class StringConverter:
    @staticmethod
    def ros2aiddl(string_msg):
        return Str(string_msg)

    @staticmethod
    def aiddl2ros(string):
        return string.string

Services

Services allow to call functions in ROS2 so we need to convert the arguments of the service call from AIDDL to ROS and the result from ROS to AIDDL. The two methods for this are request_aiddl2ros and result_ros2aiddl and their implementation is exactly as for messages. Usually service converters rely heavily on message converters (since their inputs and outputs are ROS messages).

Actions

ROS2 actions allow sending goals to action servers that are then executed over a period time. During execution, feedback messages can be provided and after execution a result message is sent. So overall we need three converters which are request_aiddl2ros to accept goals, feedback_ros2aiddl to convert feedback, and result_aiddl2ros to convert the result.

The following example converts from AIDDL to the Nav2 action NavigateToPose. (The result message of the action is empty, so the corresponding converter simply returns the constant symbol NIL.)

class NavigateToPoseConverter(object):
    @staticmethod
    def request_aiddl2ros(term: Term):
        msg = NavigateToPose.Goal()
        msg.pose = PoseStampedConverter.aiddl2ros(term[0])
        msg.behavior_tree = term[1].unpack()
        return msg

    @staticmethod
    def feedback_ros2aiddl(msg):
        msg = NavigateToPose.Feedback()
        current_pose_term = PoseStampedConverter.ros2aiddl(msg.current_pose)
        navigation_time = DurationConverter.ros2aiddl(msg.navigation_time)
        estimated_time_remaining = DurationConverter.ros2aiddl(msg.estimated_time_remaining)
        number_of_recoveries = Int(msg.number_of_recoveries)
        distance_remaining = Real(msg.distance_remaining)
        return List(
            KeyVal(Sym("current_pose"), current_pose_term),
            KeyVal(Sym("navigation_time"), navigation_time),
            KeyVal(Sym("estimated_time_remaining"), estimated_time_remaining),
            KeyVal(Sym("number_of_recoveries"), number_of_recoveries),
            KeyVal(Sym("distance_remaining"), distance_remaining)
        )

    @staticmethod
    def result_ros2aiddl(msg):
        return Sym("NIL")

Available Converters

The following table lists all available converters with the full module and class name so they can be directly used in the configuration of aiddl_ros2_bridge nodes.

Messages

Messages can be translated from AIDDL to ROS (A->R) and vice versa (R->A). The Direction column indicates which of these options are implemented in the current version. In most cases both should be supported, but some ROS topics (e.g., visualization markers) may be supported for publishing from AIDDL to ROS only since we do not anticipate wanting to read them ourselves.

Services

Actions

Open Issues

• Support direct conversions from ROS to B to avoid intermediate AIDDL conversion
• Add remaining converters from std_msgs

Version History

0.2.1

• Move constants to appropriate sub-packages
• Fix package structure to reflect ROS2 structure
• Documentation

0.1.0

• Ported functionality from ROS1 version