Run an Objective from a Custom Behavior Tree XML

DoObjectiveSequence accepts two mutually-relevant fields on its goal:

• objective_name — the name of an Objective saved in your robot configuration.
• objective_xml_string — a complete Behavior Tree XML string to execute.

If both are populated, objective_name takes precedence. Use objective_xml_string when you want to run an ad-hoc tree, wrap an existing Subtree with different port values, or compose a tree programmatically. For the basic "run a saved Objective" flow, see Run an Existing Objective.

Wrap an Existing Subtree With Custom Port Values

This pattern is the most common reason to send XML: you have a Subtree saved in the UI (for example Move to Waypoint) and you want to call it from code with different port values without authoring a new Objective for every combination.

The example below assumes the lab_sim config and sets waypoint_name="Look at Table". Change waypoint_name to another valid waypoint (for example Park Far Right) to retarget the motion.

Python (rclpy)

import rclpy
from rclpy.action import ActionClient
from rclpy.node import Node

from moveit_studio_sdk_msgs.action import DoObjectiveSequence

OBJECTIVE_XML = """
<root BTCPP_format="4" main_tree_to_execute="Move to Waypoint Remapped">
  <BehaviorTree ID="Move to Waypoint Remapped">
    <Control ID="Sequence" name="TopLevelSequence">
      <SubTree
        ID="Move to Waypoint"
        _collapsed="true"
        waypoint_name="Look at Table"
        joint_group_name="manipulator"
        controller_names="joint_trajectory_controller"
        use_all_planners="false"
      />
    </Control>
  </BehaviorTree>
</root>
"""

rclpy.init()
node = Node("custom_xml_client")
action_client = ActionClient(node, DoObjectiveSequence, "/do_objective")
action_client.wait_for_server(timeout_sec=5.0)

goal_msg = DoObjectiveSequence.Goal(objective_xml_string=OBJECTIVE_XML)
send_goal_future = action_client.send_goal_async(goal_msg)
rclpy.spin_until_future_complete(node, send_goal_future)

goal_handle = send_goal_future.result()
result_future = goal_handle.get_result_async()
rclpy.spin_until_future_complete(node, result_future)

result = result_future.result().result
print(f"Error code: {result.error_code.val}")

node.destroy_node()
rclpy.shutdown()

Python (roslibpy)

import time

import roslibpy
from roslibpy import ActionClient

OBJECTIVE_XML = """
<root BTCPP_format="4" main_tree_to_execute="Move to Waypoint Remapped">
  <BehaviorTree ID="Move to Waypoint Remapped">
    <Control ID="Sequence" name="TopLevelSequence">
      <SubTree
        ID="Move to Waypoint"
        _collapsed="true"
        waypoint_name="Look at Table"
        joint_group_name="manipulator"
        controller_names="joint_trajectory_controller"
        use_all_planners="false"
      />
    </Control>
  </BehaviorTree>
</root>
"""

client = roslibpy.Ros(host="localhost", port=3201)
client.run()

action = ActionClient(
    client,
    "/do_objective",
    "moveit_studio_sdk_msgs/action/DoObjectiveSequence",
)

done = False


def on_result(result):
    global done
    values = result.get("values", {})
    error_code = values.get("error_code", {})
    print(f"Error code: {error_code.get('val', 'unknown')}")
    print(f"Error message: {values.get('error_message', 'none')}")
    done = True


def on_feedback(feedback):
    print(f"Feedback: {feedback}")


def on_error(error):
    global done
    print(f"Action failed: {error}")
    done = True


action.send_goal({"objective_xml_string": OBJECTIVE_XML}, on_result, on_feedback, on_error)

start = time.time()
while not done and (time.time() - start) < 60:
    time.sleep(0.1)

client.terminate()

Command Line

ros2 action send_goal /do_objective moveit_studio_sdk_msgs/action/DoObjectiveSequence '
objective_xml_string: |
  <root BTCPP_format="4" main_tree_to_execute="Move to Waypoint Remapped">
    <BehaviorTree ID="Move to Waypoint Remapped">
      <Control ID="Sequence" name="TopLevelSequence">
        <SubTree
          ID="Move to Waypoint"
          _collapsed="true"
          waypoint_name="Look at Table"
          joint_group_name="manipulator"
          controller_names="joint_trajectory_controller"
          use_all_planners="false"
        />
      </Control>
    </BehaviorTree>
  </root>
'

Send a Minimal Ad-Hoc Objective

For quick verification — for example confirming the action interface is reachable — send a trivial tree:

ros2 action send_goal /do_objective moveit_studio_sdk_msgs/action/DoObjectiveSequence '
objective_xml_string: |
  <root BTCPP_format="4" main_tree_to_execute="test_simple">
    <BehaviorTree ID="test_simple">
      <Control ID="Sequence" name="TopLevelSequence">
        <Action ID="AlwaysSuccess"/>
      </Control>
    </BehaviorTree>
  </root>
'

The Objective will appear momentarily in the UI and complete with SUCCESS.

When to Use Port Remapping vs. Parameter Overrides

Two mechanisms can inject runtime values into a Behavior Tree:

• Port remapping in XML (this page) — substitute string-typed port values inside the XML you send. Best when the values are literals you already know at client compile-time and you want to express them with the same XML syntax used in the Studio editor.
• parameter_overrides — leave the XML alone and inject strongly-typed values via the parameter_overrides field on the goal. Best when the values come from outside the client (sensor data, a fleet manager, structured ROS messages such as PoseStamped).

See Passing Parameters to Objectives at Runtime for the parameter-overrides path.