navigator_lane_change

Route-aware lane-change and obstacle-bypass behavior module for Navigator.

Runs in shadow mode by default — publishes decisions and debug output with zero vehicle control authority. Execution mode is enabled by a single parameter change once the node has been validated in shadow.

Modes

Shadow mode (default)

The node observes the environment, runs the full decision pipeline, and publishes its intent — but takes no action on the vehicle. Use this to validate behavior in simulation or on a real vehicle before enabling execution.

Set in param/lane_change_params.yaml:

shadow_mode: true

Execution mode

When you are ready to allow the node to actually command lane changes, set:

shadow_mode: false

In execution mode the FSM transitions through to EXECUTE_LANE_CHANGE and the downstream trajectory node (PR 2) picks up the decision from /behavior/lane_change_decision to generate and follow a quintic path. No other code changes are needed — the interface is identical between modes.

Triggering a lane change from another node

Any node in the stack can request a lane change by publishing a single string to:

/behavior/lane_change_command   (std_msgs/String)

Valid values: "left", "right", "cancel"

Python example

from std_msgs.msg import String

# In your node's __init__:
self._lc_pub = self.create_publisher(String, '/behavior/lane_change_command', 10)

# Request a right lane change:
msg = String()
msg.data = 'right'
self._lc_pub.publish(msg)

# Request a left lane change:
msg.data = 'left'
self._lc_pub.publish(msg)

# Cancel / abort an in-progress lane change:
msg.data = 'cancel'
self._lc_pub.publish(msg)

Commands take priority over obstacle-triggered lane changes. A command expires automatically after 30 seconds — if the publishing node goes offline, the vehicle will not be left trying to change lanes indefinitely.

From the terminal (testing / manual override)

# Change to right lane
ros2 topic pub --once /behavior/lane_change_command std_msgs/msg/String "data: 'right'"

# Change to left lane
ros2 topic pub --once /behavior/lane_change_command std_msgs/msg/String "data: 'left'"

# Cancel
ros2 topic pub --once /behavior/lane_change_command std_msgs/msg/String "data: 'cancel'"

Topics

Subscribed

Published

FSM states

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