Costmap configuration (static, obstacle, inflation) in ROS

Introduction

A costmap helps a robot understand its surroundings by marking safe and unsafe areas. Configuring static, obstacle, and inflation layers lets the robot plan paths safely.

When you want the robot to avoid walls and furniture in a room.

When the robot needs to detect moving obstacles like people or pets.

When you want to keep a safe distance from obstacles to prevent collisions.

When setting up navigation for a robot in a new environment.

When tuning robot behavior to be more cautious or aggressive in path planning.

Syntax

ROS

# Example costmap_common_params.yaml
observation_sources: laser_scan_sensor

laser_scan_sensor:
  data_type: LaserScan
  topic: /scan
  marking: true
  clearing: true

# Static layer config
static_layer:
  map_topic: /map
  subscribe_to_updates: true

# Obstacle layer config
obstacle_layer:
  observation_sources: laser_scan_sensor

# Inflation layer config
inflation_layer:
  inflation_radius: 0.55
  cost_scaling_factor: 10.0

The static_layer uses a fixed map to mark known obstacles.

The obstacle_layer detects obstacles in real-time from sensors.

Examples

This setup uses only a fixed map without updates.

ROS

# Static layer only
static_layer:
  map_topic: /map
  subscribe_to_updates: false

Detects obstacles using laser scans and updates the costmap.

ROS

# Obstacle layer with laser scan
obstacle_layer:
  observation_sources: laser_scan_sensor

laser_scan_sensor:
  data_type: LaserScan
  topic: /scan
  marking: true
  clearing: true

Inflates obstacles by 0.7 meters to keep safe distance.

ROS

# Inflation layer with custom radius
inflation_layer:
  inflation_radius: 0.7
  cost_scaling_factor: 5.0

Sample Program

This is a complete costmap configuration file for ROS navigation. It combines static map data, real-time obstacle detection, and inflation to keep the robot safe.

ROS

# costmap_common_params.yaml
observation_sources: laser_scan_sensor

laser_scan_sensor:
  data_type: LaserScan
  topic: /scan
  marking: true
  clearing: true

static_layer:
  map_topic: /map
  subscribe_to_updates: true

obstacle_layer:
  observation_sources: laser_scan_sensor

inflation_layer:
  inflation_radius: 0.55
  cost_scaling_factor: 10.0

# Explanation:
# This configuration sets up a costmap with three layers:
# 1. Static layer uses a map topic to mark fixed obstacles.
# 2. Obstacle layer uses laser scans to detect moving obstacles.
# 3. Inflation layer inflates obstacles by 0.55 meters to keep safe distance.

# Output when running navigation with this config:
# The robot will avoid walls and detected obstacles,
# keeping a buffer zone around them for safety.

Important Notes

Time complexity depends on sensor data frequency and map size; inflation adds extra computation.

Space complexity grows with map resolution and sensor data.

Common mistake: setting inflation radius too small or too large affects safety and path planning.

Use static layer for known maps, obstacle layer for dynamic obstacles, and inflation to keep safe distance.

Summary

Costmaps combine static maps, obstacle detection, and inflation to help robots navigate safely.

Static layer marks fixed obstacles from a map.

Obstacle layer updates obstacles in real-time from sensors.

Inflation layer adds a safety buffer around obstacles.

Practice

1. Which costmap layer in ROS is responsible for marking fixed obstacles from a pre-existing map?

easy

A. Obstacle layer

B. Inflation layer

C. Static layer

D. Sensor layer

Solution

1. Step 1: Understand the role of the static layer

   The static layer uses a pre-built map to mark fixed obstacles that do not change over time.

2. Step 2: Compare with other layers

   The obstacle layer updates obstacles dynamically from sensors, and the inflation layer adds safety buffers, so they do not mark fixed obstacles directly.

3. Final Answer:

   Static layer -> Option C

4. Quick Check:

   Fixed obstacles = Static layer [OK]

Hint: Static layer = fixed map obstacles [OK]

Common Mistakes:

• Confusing obstacle layer with static layer
• Thinking inflation layer marks obstacles
• Assuming sensor data is static

2. Which of the following YAML snippets correctly enables the inflation layer in a ROS costmap configuration?

easy

A. inflation:
enable: true
radius: 0.5

B. inflation_layer:
active: yes
radius: 1.0

C. inflation_layer:
enabled: false
inflation_radius: 0.5

D. inflation_layer:
enabled: true
inflation_radius: 0.5

Solution

1. Step 1: Check correct keys for inflation layer

   The correct keys are 'inflation_layer' with 'enabled' and 'inflation_radius' as parameters.

2. Step 2: Validate values and syntax

   inflation_layer: enabled: true inflation_radius: 0.5 uses 'enabled: true' and 'inflation_radius: 0.5', which is correct YAML syntax and valid keys.

3. Final Answer:

   inflation_layer: enabled: true inflation_radius: 0.5 -> Option D

4. Quick Check:

   Correct keys and true enabled = inflation_layer: enabled: true inflation_radius: 0.5 [OK]

Hint: Look for 'enabled: true' and 'inflation_radius' keys [OK]

Common Mistakes:

• Using wrong key names like 'enable' or 'active'
• Setting enabled to false when enabling
• Incorrect indentation or YAML syntax

3. Given this costmap configuration snippet:

obstacle_layer:
  observation_sources: laser_scan_sensor
  laser_scan_sensor:
    data_type: LaserScan
    topic: /scan
    marking: true
    clearing: true
inflation_layer:
  inflation_radius: 0.7
  cost_scaling_factor: 10.0

What effect does setting marking: true and clearing: true have on the obstacle layer?

medium

A. It marks obstacles detected by the laser and clears free space around them

B. It disables obstacle detection and only inflates existing obstacles

C. It marks obstacles but does not clear any free space

D. It clears obstacles but does not mark new ones

Solution

1. Step 1: Understand marking and clearing flags

   Setting 'marking: true' means detected obstacles are added to the costmap. 'clearing: true' means free space detected is cleared from the costmap.

2. Step 2: Apply to laser_scan_sensor

   The laser scan sensor will mark obstacles and clear free space dynamically based on sensor data.

3. Final Answer:

   It marks obstacles detected by the laser and clears free space around them -> Option A

4. Quick Check:

   marking + clearing true = mark and clear obstacles [OK]

Hint: marking=true adds obstacles, clearing=true removes free space [OK]

Common Mistakes:

• Assuming clearing disables marking
• Thinking marking disables clearing
• Confusing cost_scaling_factor with marking

4. You have this partial costmap config:

inflation_layer:
  inflation_radius: 0.6
  cost_scaling_factor: -5.0

What is the problem with this configuration?

medium

A. inflation_radius must be an integer, not a float

B. Negative cost_scaling_factor is invalid and causes inflation errors

C. Missing 'enabled: true' disables inflation layer

D. cost_scaling_factor should be zero to disable inflation

Solution

1. Step 1: Check cost_scaling_factor value

   The cost_scaling_factor controls how quickly costs drop off from obstacles. It must be positive; negative values are invalid.

2. Step 2: Understand impact of negative value

   A negative cost_scaling_factor causes errors or unexpected inflation behavior in the costmap.

3. Final Answer:

   Negative cost_scaling_factor is invalid and causes inflation errors -> Option B

4. Quick Check:

   cost_scaling_factor < 0 = error [OK]

Hint: cost_scaling_factor must be positive [OK]

Common Mistakes:

• Thinking inflation_radius must be integer
• Assuming missing enabled disables inflation
• Believing zero cost_scaling_factor disables inflation

5. You want to configure a ROS costmap that uses a static map, detects obstacles with a laser scanner, and inflates obstacles with a radius of 0.8 meters. Which of the following combined configurations is correct?

hard

A. static_layer:
map_topic: /map
obstacle_layer:
observation_sources: laser_scan
laser_scan:
data_type: LaserScan
topic: /scan
marking: true
clearing: true
inflation_layer:
enabled: true
inflation_radius: 0.8
cost_scaling_factor: 5.0

B. static_layer:
enabled: false
obstacle_layer:
observation_sources: laser
laser:
data_type: PointCloud
topic: /scan
marking: false
clearing: true
inflation_layer:
inflation_radius: 0.8
cost_scaling_factor: -1.0

C. static_layer:
map_topic: /map
obstacle_layer:
observation_sources: laser_scan
laser_scan:
data_type: LaserScan
topic: /scan
marking: false
clearing: false
inflation_layer:
enabled: true
inflation_radius: 1.0
cost_scaling_factor: 10.0

D. static_layer:
map_topic: /map
obstacle_layer:
observation_sources: laser_scan
laser_scan:
data_type: LaserScan
topic: /scan
marking: true
clearing: false
inflation_layer:
enabled: true
inflation_radius: 0.5
cost_scaling_factor: 5.0

Solution

1. Step 1: Verify static layer configuration

   static_layer: map_topic: /map obstacle_layer: observation_sources: laser_scan laser_scan: data_type: LaserScan topic: /scan marking: true clearing: true inflation_layer: enabled: true inflation_radius: 0.8 cost_scaling_factor: 5.0 correctly sets 'static_layer' with 'map_topic: /map' to use the static map.

2. Step 2: Check obstacle layer settings

   static_layer: map_topic: /map obstacle_layer: observation_sources: laser_scan laser_scan: data_type: LaserScan topic: /scan marking: true clearing: true inflation_layer: enabled: true inflation_radius: 0.8 cost_scaling_factor: 5.0 uses 'laser_scan' with correct data_type, topic, and both marking and clearing enabled for proper obstacle detection.

3. Step 3: Confirm inflation layer parameters

   static_layer: map_topic: /map obstacle_layer: observation_sources: laser_scan laser_scan: data_type: LaserScan topic: /scan marking: true clearing: true inflation_layer: enabled: true inflation_radius: 0.8 cost_scaling_factor: 5.0 enables inflation with radius 0.8 and a positive cost_scaling_factor, matching requirements.

4. Final Answer:

   static_layer: map_topic: /map obstacle_layer: observation_sources: laser_scan laser_scan: data_type: LaserScan topic: /scan marking: true clearing: true inflation_layer: enabled: true inflation_radius: 0.8 cost_scaling_factor: 5.0 -> Option A

5. Quick Check:

   All layers correct and enabled = static_layer: map_topic: /map obstacle_layer: observation_sources: laser_scan laser_scan: data_type: LaserScan topic: /scan marking: true clearing: true inflation_layer: enabled: true inflation_radius: 0.8 cost_scaling_factor: 5.0 [OK]

Hint: Check all layers enabled with correct parameters [OK]

Common Mistakes:

• Disabling static layer or obstacle marking
• Using negative cost_scaling_factor
• Setting inflation_radius different from 0.8