easynav_costmap_planner

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README

easynav_costmap_planner

Description

A planner plugin implementing a standard A* path planner over a Costmap2D representation. It reads the dynamic costmap, goal list, and robot pose from NavState and publishes a computed path as a nav_msgs/Path message.

Authors and Maintainers

• Authors: Intelligent Robotics Lab

• Maintainers: Francisco Martín Rico fmrico@gmail.com

Supported ROS 2 Distributions

Distribution	Status
humble
jazzy
kilted
rolling

Plugin (pluginlib)

• Plugin Name: easynav_costmap_planner/CostmapPlanner

• Type: easynav::CostmapPlanner

• Base Class: easynav::PlannerMethodBase

• Library: easynav_costmap_planner

• Description: A default Costmap2D-based A* path planner implementation.

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Parameters

All parameters are declared under the plugin namespace, i.e., /<node_fqn>/easynav_costmap_planner/CostmapPlanner/....

Name	Type	Default	Description
<plugin>.cost_factor	double	2.0	Scaling factor applied to costmap cell values to compute traversal costs. Higher values make high-cost cells much less attractive.
<plugin>.inflation_penalty	double	5.0	Extra penalty added to inflated/near-obstacle cells to push paths away from obstacles.
<plugin>.heuristic_scale	double	1.0	Scaling factor applied to the A* heuristic term. Controls the trade-off between following the cheapest route vs. going more directly.
<plugin>.continuous_replan	bool	true	If true, re-plans continuously as the map/goal changes; if false, plans once per request.

Effect of cost_factor

The planner uses a per-step traversal cost:

$$ g_{\text{new}} = g_{\text{current}} + \text{step_cost} \cdot \left(1 + \text{cost_factor} \cdot \frac{\text{cell_cost}}{\text{LETHAL_OBSTACLE}}\right) $$

• Low cost_factor (e.g. 1–2):

  • Cell cost has a modest influence; the planner is closer to a pure geometric shortest-path search.

  • Paths may cross moderately expensive regions if that keeps distance short.

• High cost_factor (e.g. 5–10+):

  • High-cost cells become very unattractive, so the planner strongly prefers low-cost corridors (e.g. routes or low-inflation areas), even if they are longer.

  • Useful when combined with modules that encode preferences as higher costs (such as route managers).

Effect of heuristic_scale

The A* priority is:

$$ f = g + h, \quad h = \text{heuristic_scale} \cdot d_{\text{cells}}(\text{current}, \text{goal}) $$

where $d_{\text{cells}}$ is the Euclidean distance in cell indices (not metric distance, but proportional).

• Decrease heuristic_scale (< 1.0):

  • The heuristic term becomes weaker, and A* behaves more like Dijkstra.

  • The search explores more alternatives and is guided more strictly by the true accumulated cost $g$.

  • This usually makes the planner follow high-cost penalties (e.g. for leaving a route) more faithfully, at the expense of more computation.

• Increase heuristic_scale (> 1.0):

  • The heuristic term dominates more, so the planner prefers geometrically direct paths.

  • It may still avoid extremely high-cost regions if cost_factor is large, but will be more willing to “cut corners” through slightly more expensive zones.

Typical tuning strategy:

• First, adjust cost_factor so that the costmap properly encodes your preferences:

  • Increase it until paths clearly avoid high-cost areas that should be disfavored.

• Then, fine-tune heuristic_scale:

  • Start from 1.0.

  • If the planner still takes shortcuts that ignore cost differences, consider reducing it slightly (e.g. 0.7–0.9).

  • If planning becomes too slow or explores too widely, you can increase it modestly (e.g. 1.2–1.5).

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Interfaces (Topics and Services)

Publications

Direction	Topic	Type	Purpose	QoS
Publisher	<node_fqn>/<plugin>/path	nav_msgs/msg/Path	Publishes the computed path from start to goal.	depth=10

This plugin does not create subscriptions or services directly; it reads inputs via NavState.

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NavState Keys

Key	Type	Access	Notes
goals	nav_msgs::msg::Goals	Read	Goal list used as planner targets.
map.dynamic	Costmap2D	Read	Dynamic costmap used for A* search.
robot_pose	nav_msgs::msg::Odometry	Read	Current robot pose used as the start position.
path	nav_msgs::msg::Path	Write	Output path to follow.

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TF Frames

Role	Transform	Notes
Reads	map -> base_footprint	Requires consistent frames between the costmap and the published path.

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License

Apache-2.0