Interactive markers for teleoperation in ROS - Performance & Optimization

Performance: Interactive markers for teleoperation

MEDIUM IMPACT

This concept affects the responsiveness and smoothness of user interactions with robot controls in the browser or GUI, impacting input delay and visual stability.

Updating interactive markers for robot teleoperation controls

ROS

void onMarkerInteraction() {
  updateMarkerPose();
  publishMarker();
}
// Only update when user interacts

Updates only occur on user interaction events, reducing CPU and network usage and improving responsiveness.

📈 Performance Gainnon-blocking updates, reduces input lag by 50% or more

Updating interactive markers for robot teleoperation controls

ROS

while (true) {
  updateMarkerPose();
  publishMarker();
  ros::Duration(0.01).sleep();
}

Continuously publishing marker updates at a fixed high rate causes unnecessary CPU load and network traffic, leading to input lag and jitter.

📉 Performance Costblocks rendering for 10-20ms per update, triggers frequent UI thread stalls

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Continuous high-rate updates	High (many marker redraws)	Many (each update triggers reflow)	High (frequent repaints)	[X] Bad
Event-driven updates	Low (only on interaction)	Few (minimal reflows)	Low (less repainting)	[OK] Good

Rendering Pipeline

Interactive marker updates flow through event handling, pose calculation, and rendering stages. Frequent updates cause repeated layout recalculations and repaints.

→Event Handling

→Pose Calculation

→Layout

→Paint

→Composite

⚠️ BottleneckLayout and Paint stages due to frequent marker position changes

Core Web Vital Affected

INP

This concept affects the responsiveness and smoothness of user interactions with robot controls in the browser or GUI, impacting input delay and visual stability.

Optimization Tips

1Avoid continuous high-frequency updates; update markers only on interaction.

2Throttle or debounce marker updates to reduce layout and paint costs.

3Monitor rendering pipeline stages to identify and fix bottlenecks.

Performance Quiz - 3 Questions

What is the main performance issue with continuously publishing interactive marker updates at a fixed high rate?

A It reduces memory usage by frequent clearing

B It causes unnecessary CPU and network load leading to input lag

C It improves responsiveness by updating constantly

D It prevents layout recalculations

DevTools: Performance

How to check: Record a session while interacting with markers. Look for long tasks or frequent layout and paint events in the flame chart.

What to look for: High frequency of layout and paint events indicates inefficient updates; fewer and shorter events indicate good performance.

Practice

1. What is the main purpose of interactive markers in ROS teleoperation?

easy

A. To visually control robots by moving markers in 3D space

B. To write robot control code without any user input

C. To display static images of the robot status

D. To log robot sensor data for offline analysis

Solution

1. Step 1: Understand interactive markers role

   Interactive markers allow users to move and rotate markers in a 3D view to control robots easily.

2. Step 2: Compare options with purpose

   Only To visually control robots by moving markers in 3D space describes visual control via markers; others describe unrelated tasks.

3. Final Answer:

   To visually control robots by moving markers in 3D space -> Option A

4. Quick Check:

   Interactive markers = Visual robot control [OK]

Hint: Interactive markers let you move robot parts visually [OK]

Common Mistakes:

• Thinking markers are only for displaying data
• Confusing teleoperation with offline logging
• Assuming no user input is needed

2. Which ROS message type is commonly used to create an interactive marker for teleoperation?

easy

A. std_msgs/String

B. sensor_msgs/Image

C. geometry_msgs/Twist

D. visualization_msgs/InteractiveMarker

Solution

1. Step 1: Identify message type for interactive markers

   The message type visualization_msgs/InteractiveMarker is designed to define interactive markers in ROS.

2. Step 2: Eliminate unrelated message types

   sensor_msgs/Image is for images, geometry_msgs/Twist for velocity commands, std_msgs/String for text messages, so they don't create interactive markers.

3. Final Answer:

   visualization_msgs/InteractiveMarker -> Option D

4. Quick Check:

   Interactive marker message = visualization_msgs/InteractiveMarker [OK]

Hint: Interactive markers use visualization_msgs/InteractiveMarker type [OK]

Common Mistakes:

• Choosing geometry_msgs/Twist which is for velocity commands
• Confusing image or string messages with markers
• Not knowing ROS message types

3. Given this snippet handling interactive marker feedback in ROS:

void processFeedback(const visualization_msgs::InteractiveMarkerFeedbackConstPtr &feedback) {
  if (feedback->event_type == visualization_msgs::InteractiveMarkerFeedback::POSE_UPDATE) {
    geometry_msgs::Pose new_pose = feedback->pose;
    // Update robot command with new_pose
  }
}

What happens when the user moves the marker?

medium

A. The robot command updates with the marker's new pose

B. The marker resets to its original position

C. The feedback event_type is ignored

D. The robot stops moving immediately

Solution

1. Step 1: Analyze feedback event type

   The code checks if the event_type is POSE_UPDATE, which means the marker was moved or rotated.

2. Step 2: Understand the effect of POSE_UPDATE

   When POSE_UPDATE occurs, the new pose is extracted and used to update the robot command, so the robot moves accordingly.

3. Final Answer:

   The robot command updates with the marker's new pose -> Option A

4. Quick Check:

   POSE_UPDATE triggers robot command update [OK]

Hint: POSE_UPDATE means marker moved, update robot pose [OK]

Common Mistakes:

• Assuming marker resets automatically
• Ignoring the event_type check
• Thinking robot stops without command

4. You wrote this callback for interactive marker feedback but the robot does not move:

void feedbackCallback(const visualization_msgs::InteractiveMarkerFeedbackConstPtr &feedback) {
  if (feedback->event_type = visualization_msgs::InteractiveMarkerFeedback::POSE_UPDATE) {
    // update robot command
  }
}

What is the error?

medium

A. Missing return statement in the callback

B. Using assignment '=' instead of comparison '==' in the if condition

C. Incorrect message type for feedback parameter

D. Not publishing the updated robot command

Solution

1. Step 1: Check the if condition syntax

   The condition uses '=' which assigns a value instead of '==' which compares values.

2. Step 2: Understand effect of assignment in if

   Assignment always returns true, so the condition is always true but does not properly check event_type, causing logic errors.

3. Final Answer:

   Using assignment '=' instead of comparison '==' in the if condition -> Option B

4. Quick Check:

   Use '==' to compare event_type, not '=' [OK]

Hint: Use '==' to compare, '=' assigns value [OK]

Common Mistakes:

• Confusing '=' and '==' in conditions
• Assuming missing return causes no movement
• Ignoring need to publish commands

5. You want to create an interactive marker that allows the user to rotate a robot arm joint only around the Z axis. Which control type and orientation should you use in your marker setup?

hard

A. Use a BUTTON control with no orientation

B. Use a MOVE_PLANE control with orientation aligned to the X axis

C. Use a ROTATE_AXIS control with orientation set to align Z axis with the joint axis

D. Use a MOVE_AXIS control aligned to the Y axis

Solution

1. Step 1: Identify control type for rotation

   ROTATE_AXIS control allows rotation around a single axis, suitable for rotating a joint.

2. Step 2: Set orientation to align with joint axis

   To rotate around Z axis, set the control's orientation so its Z axis matches the joint's rotation axis.

3. Final Answer:

   Use a ROTATE_AXIS control with orientation set to align Z axis with the joint axis -> Option C

4. Quick Check:

   ROTATE_AXIS + Z orientation = rotate joint around Z [OK]

Hint: ROTATE_AXIS control with Z orientation rotates joint around Z [OK]

Common Mistakes:

• Using MOVE_PLANE which moves in a plane, not rotate
• Choosing BUTTON which is for clicks, not rotation
• Aligning control to wrong axis