ERC_NAV — Xplore Navigation Workspace 2026

ROS 2 Humble workspace for the EPFL Xplore rover's autonomous navigation stack, for the European Rover Challenge.

• TL: Paul Bourgois
• SE: Arno Laurie
• Documentation (Notion): https://www.notion.so/xplore-doc/Navigation-128d2c11ab574c95a9be0790afa76d48

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Overview

The stack takes readings from the rover's sensors (LiDAR, IMU, wheel encoders, cameras), fuses them into a single odom → base_link transform, builds a local traversability costmap, and lets Nav2 plan and follow a path that the wheel controller turns into individual motor commands.

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Repository layout

Folder	Contents
custom_msg/	Motor status / command ROS messages shared across the stack.
interfacing_nav_cs/	Interface node with the Command Station.
jetson_stats/	Publishes Jetson telemetry.
localization/camera/	ArUco tag stack: ros2_aruco_cpp (multi-view detector), ros2_aruco_with_lidar (LiDAR-assisted refinement), ros2_aruco_interfaces (messages), nav_global_loc_convex (global localization).
localization/lidar/	glim_starter (GLIM LiDAR SLAM wrapper) and liorf (alternative LiDAR-inertial odometry).
localization/nav_ekf/local_nav_ekf/	Custom EKF fusing wheel odometry, IMU, ArUco, LiDAR, VIO. Builds two executables: nav_ekf_node (2D) and nav_ekf_3d_node (3D, with RK4 prediction + Joseph-form updates).
localization/odom_preprocessor/	Small helpers to re-publish/align odometry streams.
localization/wheels_odometry/	Kinematic wheel odometry math kept as a pure-CMake Eigen lib.
navigation/gradient_costmap/	traversability_filter, traversability_map, and the Nav2 costmap gradient_layer_plugin.
navigation/path_planning/	Nav2 launch files + config/nav2_params_real_2026_no_global_map.yaml tuned for ERC 2026.
sensors/camera/ERC_CAMERAS/	Camera driver and per-camera launch files (nav / high-def / command-station).
sensors/imu/olive_imu_restamper/	Restamps the Olive IMU to current ROS time. Ships calibration scripts.
sensors/imu/ouster_imu_tester/	Diagnostic tool for the Ouster built-in IMU.
sensors/lidar/ros2_ouster_drivers/	Vendored Ouster driver (OS-0 / OS-1).
wheels_control/	Gamepad and CS teleop, cmd_vel manager, displacement commands, motor command bridge, steering slip controller, wheel odometry node.
xplore_description/	URDF + robot state publisher launches (real and sim).
docker_humble_*/	Reference Docker images for desktop, GLIM, and Jetson targets.

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Main launch entry points

All commands assume the workspace has been sourced:

source install/setup.bash

Manual driving + sensing + localization

ros2 launch wheels_control manual_stack.launch.py

Starts, in order:

• Command-station interface, gamepad teleop, cmd_vel manager, displacement commands, motor command bridge (NAV_motor_cmds), and the steering slip controller.
• xplore_description URDF / robot state publisher (pub_urdf:=true by default).
• Olive IMU restamper.
• Wheel odometry node.
• local_nav_ekf/nav_ekf_node with include_lidar:=true, include_aruco:=false, include_vio:=false.
• Ouster LiDAR driver (ros2_ouster).
• NAV cameras (camera/camera_node_nav.launch.py).
• 7 s later: ros2_aruco_cpp multi-view ArUco detector and ros2_aruco_with_lidar (lidar_phi_filter_node + detect_cube) for LiDAR-refined cube centroids.
• Jetson stats publisher.

Useful launch args:

• motor_cmds (default true) — skip motor bridge when bench-testing.
• homing (default false) — run the homing sequence on startup.
• pub_urdf (default true) — publish URDF + launch the Ouster driver.

Full autonomous stack (manual stack + costmap + Nav2)

ros2 launch path_planning autonomous_stack.launch.py

This wraps manual_stack.launch.py and then:

• At t = 30 s: gradient_costmap.launch.py in local mode, which spawns traversability_filter (point cloud transform + height map), traversability_map (local occupancy + cost), and the gradient_layer_plugin consumed by Nav2 costmaps.
• At t = 35 s: the full Nav2 stack (controller_server, planner_server, bt_navigator, behavior_server, waypoint_follower, velocity_smoother, smoother_server, map_server, lifecycle_manager) configured from navigation/path_planning/config/nav2_params_real_2026_no_global_map.yaml. Nav2 publishes to cmd_vel_nav, which the wheel controller consumes.

The delays are intentional: the Ouster TF tree typically settles around 28–30 s after boot.

Other useful launch files

• navigation/path_planning/launch/nav2_real.launch.py — Nav2 only (no manual stack).
• navigation/path_planning/launch/localization_launch.py — Nav2 localization subset.
• navigation/path_planning/launch/liorf_testing.launch.py — LIORF bring-up for SLAM experiments.
• localization/lidar/glim_starter/launch/glim_starter.launch.py — GLIM LiDAR SLAM.
• sensors/lidar/ros2_ouster_drivers/ros2_ouster/launch/driver_launch.py — Ouster driver alone.
• xplore_description/launch/xplore_sim.launch.py — URDF in simulation.

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Key components

local_nav_ekf

Custom Extended Kalman Filter with two variants:

• nav_ekf_node — 2D filter, state [x, y, yaw, vx, vy]. The default used by manual_stack.launch.py.
• nav_ekf_3d_node — 3D filter, state [x, y, z, roll, pitch, yaw, vx, vy, vz]. Mean prediction uses RK4 integration of the full nonlinear kinematics; covariance prediction uses a RK2-discretized constant-velocity Jacobian; posterior covariance updates use the Joseph form with explicit symmetrization. Roll and pitch are IIR low-passed before the IMU update to reject chassis vibration. Publishes odom → base_link with full 3D translation and rotation so downstream nodes (traversability filter, gradient costmap) see rover pitch/roll.

Parameters (3D node): include_lidar, include_aruco, include_vio, roll_pitch_lowpass_tau, mahalanobis_gate_squared. Output: /fused_nav_ekf_odom.

ArUco + LiDAR cube detection (ros2_aruco_with_lidar)

Two-stage pipeline used to refine camera ArUco detections with the LiDAR:

1. lidar_phi_filter_node — spatial pre-filter. Associates every valid camera detection (outside a forbidden angular sector) with a hard-coded map landmark and keeps only LiDAR points that fall inside vertical cylinders around the associated landmarks.
2. detect_cube — runs sequential 3D RANSAC line fits on the pre-filtered cloud, projects inliers to 2D, re-RANSACs, and builds candidate cube centroids using the known cube side length. The radial gate uses the expected range from map_frame to the sensor (not the noisy camera range) to stay consistent with the map.

See localization/camera/ros2_aruco_with_lidar/docs/LIDAR_ARUCO_NODES.md for the detailed math and parameter reference.

Gradient costmap (navigation/gradient_costmap)

• traversability_filter transforms the raw Ouster cloud into a fixed frame (using the TF tree, so it honours rover roll/pitch when those are published) and builds a local height map.
• traversability_map fits local planes to cells to produce a slope/roughness occupancy grid.
• gradient_layer_plugin exposes that grid as a Nav2 costmap layer (read from topic or from a PGM/YAML pair in global mode).

Wheel control (wheels_control)

Implements the Xplore-specific kinematics: independent steering per wheel with Ackermann, in-place rotation, and straight-drive cases. Provides the manual/teleop path used outside of Nav2 and the motor bridge for all modes.

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Build

# First-time build (fetches dependencies order)
colcon build --symlink-install

# Iterating on a single package
colcon build --packages-select local_nav_ekf --symlink-install

# Source and run
source install/setup.bash

Docker images for the desktop, Jetson, and GLIM-enabled targets live under docker_humble_desktop/, docker_humble_jetson/, and docker_humble_glim/.

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LiDAR (Ouster) ethernet setup

The Ouster needs a static IPv4 on whatever interface it is plugged into, plus a small DHCP range for the sensor to pull its lease from.

If the LiDAR is connected to eth0

sudo ip addr flush dev eth0
sudo ip link set eth0 down
sudo ip addr show dev eth0   # should report state DOWN
sudo ip addr add 10.5.5.1/24 dev eth0
sudo ip link set eth0 up
sudo ip addr show eth0
sudo dnsmasq -C /dev/null -kd -F 10.5.5.50,10.5.5.100 -i eth0 --bind-dynamic

If the LiDAR is connected to eth1

sudo ip addr flush dev eth1
sudo ip link set eth1 down
sudo ip addr show dev eth1   # should report state DOWN
sudo ip addr add 10.5.5.1/24 dev eth1
sudo ip link set eth1 up
sudo ip addr show eth1
sudo dnsmasq -C /dev/null -kd -F 10.5.5.50,10.5.5.100 -i eth1 --bind-dynamic

Quick sanity checks

Web UI: http://os-122140001125.local

nmcli connection show
avahi-browse -arlt
ping 10.5.5.87
ping 10.5.5.1
pinglidar            # alias for: ping os-122140001125.local
nc os-122140001125.local

Manual static IPv4 (if all else fails)

sudo ip addr add 10.5.5.1/24 dev <iface> mtu 1500