Waypoint Navigation

The UGV uses Nav2 for autonomous navigation with GPS waypoints. The navigation stack is configured through several parameter files that control different aspects of the navigation system.

To learn more about Nav2, refer to the official documentation.

Global Route Planning

The global planner generates an optimal path from the robot’s current position to the goal. We use the SMAC Hybrid-A* planner with the following key parameters:

planner_server:
  ros__parameters:
    planner_plugins: ["GridBased"]
    GridBased:
      plugin: "nav2_smac_planner/SmacPlannerHybrid"
      tolerance: 0.25                     # Goal tolerance in meters
      allow_unknown: true                 # Allow planning through unknown space
      max_planning_time: 5.0              # Maximum time allowed for planning
      motion_model_for_search: "DUBIN"    # Use Dubins car motion model
      minimum_turning_radius: 0.40        # Minimum turning radius in meters

Local Trajectory Control

For local trajectory control, multiple controller options are available:

Regulated Pure Pursuit (RPP)

The RPP controller provides smooth path following with obstacle avoidance:

controller_server:
  ros__parameters:
    controller_plugins: ["FollowPath"]
    FollowPath:
      plugin: "nav2_regulated_pure_pursuit_controller::RegulatedPurePursuitController"
      desired_linear_vel: 0.5             # Maximum forward velocity
      lookahead_dist: 0.6                 # Base lookahead distance
      min_lookahead_dist: 0.3             # Minimum lookahead distance
      max_lookahead_dist: 0.9             # Maximum lookahead distance
      use_velocity_scaled_lookahead_dist: false
      use_collision_detection: true        # Enable collision checking

Vector Pursuit

The Vector Pursuit controller offers an alternative approach:

controller_server:
  ros__parameters:
    controller_plugins: ["FollowPath"]
    FollowPath:
      plugin: "vector_pursuit_controller::VectorPursuitController"
      desired_linear_vel: 0.5             # Maximum forward velocity
      min_turning_radius: 0.25            # Minimum turning radius
      lookahead_dist: 1.0                 # Base lookahead distance
      use_collision_detection: true        # Enable collision checking

Behavior Server

The behavior server manages recovery behaviors when the robot encounters difficulties:

behavior_server:
  ros__parameters:
    behavior_plugins: ["spin", "backup", "drive_on_heading", "wait"]
    spin:
      plugin: "nav2_behaviors/Spin"       # Rotate in place
    backup:
      plugin: "nav2_behaviors/BackUp"     # Move backwards
    drive_on_heading:
      plugin: "nav2_behaviors/DriveOnHeading"  # Drive straight
    wait:
      plugin: "nav2_behaviors/Wait"       # Wait in place

Costmap Configuration

Both global and local costmaps are configured to handle obstacles:

local_costmap:
  local_costmap:
    ros__parameters:
      update_frequency: 5.0
      publish_frequency: 2.0
      width: 3                            # Local costmap width in meters
      height: 3                           # Local costmap height in meters
      resolution: 0.05                    # Resolution in meters/cell
      robot_radius: 0.18                  # Robot radius for collision checking

global_costmap:
  global_costmap:
    ros__parameters:
      update_frequency: 1.0
      publish_frequency: 1.0
      resolution: 0.05                    # Resolution in meters/cell
      track_unknown_space: true           # Track unknown areas

GPS Integration

To allow the robot to navigate through coordinates in the WGS84 reference frame, a Quectel L-80 M39 GPS (GPS3 Click module) with a TTL-USB adapter is used.

The GPS waypoints are processed through a dedicated node (osr_autonomous/gps_follower.py) that converts GPS coordinates to map coordinates (using UTM projection) and sends them to Nav2’s waypoint follower:

GPS module.

waypoint_follower:
  ros__parameters:
    loop_rate: 20
    stop_on_failure: false
    waypoint_task_executor_plugin: "wait_at_waypoint"
    wait_at_waypoint:
      plugin: "nav2_waypoint_follower::WaitAtWaypoint"
      enabled: True
      waypoint_pause_duration: 200        # Time to wait at each waypoint (ms)

The GPS interface node subscribes to waypoints published in GPS coordinates and transforms them to the map frame before sending them to Nav2 for execution.