Collision avoidance in planning in ROS - Performance & Optimization

Performance: Collision avoidance in planning

HIGH IMPACT

This affects the robot's path planning speed and responsiveness during navigation, impacting how quickly and smoothly it can avoid obstacles.

Planning a path while avoiding obstacles in a dynamic environment

ROS

use_incremental_planner = True
while planning_path:
    if detect_nearby_obstacle(robot_position):
        update_local_path_segment()
    else:
        continue_current_path()

Only replans small local segments when necessary, reducing computation and improving responsiveness.

📈 Performance Gainreduces planning delay to under 10 ms per update, improving interaction speed

Planning a path while avoiding obstacles in a dynamic environment

ROS

while planning_path:
    for obstacle in all_obstacles:
        if check_collision(robot_path, obstacle):
            replan_entire_path()
            break

This approach checks all obstacles every time and replans the entire path immediately, causing frequent heavy computations and delays.

📉 Performance Costblocks planning for 100+ ms per replan, causing input lag and slow response

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Full path replanning on every obstacle detection	N/A	N/A	N/A	[X] Bad
Incremental local replanning with obstacle proximity checks	N/A	N/A	N/A	[OK] Good

Rendering Pipeline

Collision avoidance planning flows through sensor data processing, path computation, and motion command generation. Heavy computations here delay the robot's movement updates.

→Sensor Data Processing

→Path Planning Computation

→Motion Command Update

⚠️ BottleneckPath Planning Computation is most expensive due to collision checks and replanning.

Core Web Vital Affected

INP

This affects the robot's path planning speed and responsiveness during navigation, impacting how quickly and smoothly it can avoid obstacles.

Optimization Tips

1Avoid full path replanning on every obstacle detection to reduce blocking delays.

2Use incremental or local replanning algorithms to limit computation to affected path segments.

3Leverage spatial data structures and proximity checks to minimize unnecessary collision checks.

Performance Quiz - 3 Questions

What is the main performance issue with replanning the entire path on every obstacle detection?

A It uses too little memory, causing inefficiency.

B It causes frequent heavy computations leading to slow response times.

C It improves responsiveness by always having the latest path.

D It reduces sensor data processing time.

DevTools: ros2_tracing or rqt_graph

How to check: Use ros2_tracing to record planning node execution times and rqt_graph to visualize node communication delays.

What to look for: Look for long blocking times in planning callbacks and frequent full replanning triggers indicating performance bottlenecks.

Practice

1. What is the main purpose of collision avoidance in ROS planning?

easy

A. To make the robot ignore obstacles and move freely

B. To prevent the robot from hitting obstacles while moving

C. To speed up the robot's movement regardless of obstacles

D. To stop the robot from moving at all

Solution

1. Step 1: Understand collision avoidance goal

   Collision avoidance means the robot should not bump into objects while moving.

2. Step 2: Identify correct purpose

   The main goal is to keep the robot safe by avoiding obstacles during planning.

3. Final Answer:

   To prevent the robot from hitting obstacles while moving -> Option B

4. Quick Check:

   Collision avoidance = prevent hitting obstacles [OK]

Hint: Collision avoidance means safety, not speed or stopping [OK]

Common Mistakes:

• Thinking collision avoidance speeds up movement
• Believing robot ignores obstacles
• Assuming robot should stop moving

2. Which ROS component is used to add obstacles for collision avoidance during planning?

easy

A. Planning Scene

B. Move Group Interface

C. Robot State Publisher

D. Joint State Listener

Solution

1. Step 1: Identify obstacle representation in ROS planning

   Obstacles are added to the planning scene to inform the planner about their presence.

2. Step 2: Match component to function

   The Planning Scene holds information about obstacles and environment for collision checking.

3. Final Answer:

   Planning Scene -> Option A

4. Quick Check:

   Obstacles added via Planning Scene [OK]

Hint: Obstacles go into the Planning Scene, not robot state [OK]

Common Mistakes:

• Confusing Move Group Interface with obstacle storage
• Thinking Robot State Publisher manages obstacles
• Assuming Joint State Listener adds obstacles

3. Given this ROS planning code snippet, what will happen if the planner finds no valid path?

move_group.setStartStateToCurrentState()
move_group.setPoseTarget(target_pose)
plan = move_group.plan()
if plan:
    move_group.execute(plan)
else:
    print("No valid path found")

medium

A. The robot moves to the target pose anyway

B. The robot moves to a random position

C. The robot prints "No valid path found" and does not move

D. The planner crashes with an error

Solution

1. Step 1: Analyze the plan check condition

   The code checks if plan is valid (truthy). If not, it prints a message.

2. Step 2: Understand behavior when no path found

   If no valid path, the else block runs, printing "No valid path found" and skipping execution.

3. Final Answer:

   The robot prints "No valid path found" and does not move -> Option C

4. Quick Check:

   No path means print message, no movement [OK]

Hint: Check plan validity before execute to avoid errors [OK]

Common Mistakes:

• Assuming robot moves without a valid plan
• Expecting a crash instead of safe handling
• Thinking robot moves randomly

4. Identify the error in this ROS planning snippet that prevents collision avoidance:

planning_scene = PlanningSceneInterface()
obstacle = CollisionObject()
obstacle.id = "box"
obstacle.header.frame_id = "world"
# Missing shape and pose assignment here
planning_scene.addCollisionObjects([obstacle])

medium

A. The obstacle has no shape or pose defined

B. The planning scene is not initialized

C. The obstacle ID is missing

D. The frame_id should be "base_link"

Solution

1. Step 1: Check obstacle definition

   The obstacle lacks shape and pose, so it has no physical presence.

2. Step 2: Understand impact on collision avoidance

   Without shape and pose, the planner cannot detect or avoid the obstacle.

3. Final Answer:

   The obstacle has no shape or pose defined -> Option A

4. Quick Check:

   Obstacle needs shape and pose to exist [OK]

Hint: Always define shape and pose for obstacles [OK]

Common Mistakes:

• Ignoring shape and pose assignment
• Thinking frame_id must be base_link always
• Assuming missing ID causes failure

5. You want to ensure your robot avoids a newly added obstacle during planning. Which sequence correctly updates the planning scene and checks for a valid path before moving?

hard

A. Only call plan() without adding obstacle

B. Call execute() first, then add obstacle, then plan()

C. Add obstacle, execute plan without checking validity

D. Add obstacle to Planning Scene, call plan(), check if plan valid, then execute plan

Solution

1. Step 1: Add obstacle to Planning Scene

   Adding the obstacle updates the environment for collision checking.

2. Step 2: Plan and check validity before execution

   Call plan() to find a path avoiding obstacles, then verify plan is valid before executing.

3. Step 3: Avoid unsafe execution

   Executing without a valid plan or before adding obstacles risks collisions or errors.

4. Final Answer:

   Add obstacle to Planning Scene, call plan(), check if plan valid, then execute plan -> Option D

5. Quick Check:

   Update scene, plan, validate, then execute [OK]

Hint: Always add obstacles before planning and check plan validity [OK]

Common Mistakes:

• Executing before planning
• Not adding obstacles before planning
• Skipping plan validity check