Nav2 Traversability Plugin

Overview

The Nav2 Traversability Plugin generates traversability costmaps for outdoor terrains. The plugin utilizes LiDAR data to create heightmaps, gradient maps. The traverssability layer is generated by thresholding the gradient map and is intergrated as a custom Nav2 costmap layer.

Configuration

The traversability_params.yaml file contains configuration parameters for various modules:

Section	Parameter	Description
traversability/*	norm_max	Maximum value for normalization.
	norm_min	Minimum value for normalization.
	min_height	Minimum height value for the heightmap.
	max_height	Maximum height value for the heightmap.
	out_frame	Output frame of reference (set to odom).
traversability/fused_traversability_map	max_gradient	Maximum gradient value for the gradeint map.
	min_gradient	Minimum gradient value for the gradeint map.
	traversability_max_gradient	Maximum allowed gradient above which terrain is NOT traversable.
	traversability_min_gradient	Minimum gradient below which terrain is traversable.
	process_noise	Process noise for filtering.
	measurement_noise	Measurement noise for filtering.
	clear_map_after	Time (seconds) after which to clear the map.
	save_map	Boolean to save the map.
	publish_fused_heightmap	Boolean to publish the fused heightmap.
	save_map_interval	Interval (seconds) to save the map.
	publish_map_interval	Interval (seconds) to publish the map.
	subscription_topic	Topic for subscribing to the heightmap.
	global_heightmap_topic	Topic for the global heightmap.
	fused_heightmap_topic	Topic for the fused heightmap.
	traversability_topic	Topic for the traversability map.
traversability/pointcloud_to_heightmap	subscription_topic	Topic for subscribing to the point cloud.
	heightmap_topic	Topic for the heightmap output.
	gradientmap_topic	Topic for the gradient map output.
	traversability_topic	Topic for the traversability map output.
	resolution	Resolution of the heightmap (meters per cell).
	max_range	Maximum range to consider in the heightmap (meters).
	robot_footprint	Radius of the robot footprint (meters).
	gradient_threshold	Threshold for gradient calculations.
	sensor_frame	Frame of reference for the sensor.
	robot_frame	Frame of reference for the robot.
	timeout_duration	Timeout duration for transform buffer (seconds).

Custom Messages

• GridMap16.msg: This message type stores the heightmap data as int16 values for better resolution.
• QuadSurface.msg: The QuadSurface message holds an array of Quad messages and origin information. The Quad message type represents a quadrilateral in 3D space with four vertices. Each vertex is a point in 3D space, ordered as bottom-left, bottom-right, top-right, and top-left.

Visualising Terrain Surface

• The custom RViz plugin (z_surface_rviz_plugin) can be used to visualize terrain surface. A helper node is provided in /traversability/traversability/terrain_surface.py