Interactive markers for teleoperation in ROS - Mini Project: Build & Apply

Interactive markers for teleoperation

📖 Scenario: You are building a simple teleoperation interface for a robot using ROS interactive markers. The robot operator will move a marker in RViz to control the robot's position.

🎯 Goal: Create a ROS node that sets up an interactive marker with a control to move it in 3D space. The marker's position updates should be published for the robot to follow.

📋 What You'll Learn

Create an interactive marker server

Define an interactive marker with a move control

Implement a feedback callback to handle marker movement

Publish the updated marker pose for teleoperation

💡 Why This Matters

🌍 Real World

Interactive markers allow robot operators to intuitively control robot positions in 3D space using RViz, improving teleoperation efficiency and safety.

💼 Career

Understanding interactive markers is essential for robotics engineers working on human-robot interfaces, teleoperation systems, and robot visualization.

1

Create the interactive marker server

Write code to import the interactive_markers package and create an InteractiveMarkerServer named server with the name "teleop_marker".

ROS

# Import interactive_markers and create InteractiveMarkerServer named server
# Your code here

Hint

Use InteractiveMarkerServer from interactive_markers.interactive_marker_server and name it server.

2

Define the interactive marker and move control

Create an InteractiveMarker named int_marker with the frame_id set to "base_link" and name "teleop_marker". Then create a InteractiveMarkerControl named move_control with the interaction_mode set to InteractiveMarkerControl.MOVE_3D and add it to int_marker.controls.

ROS

from interactive_markers.interactive_marker_server import InteractiveMarker, InteractiveMarkerControl

# Create InteractiveMarker named int_marker
# Create InteractiveMarkerControl named move_control with MOVE_3D mode
# Add move_control to int_marker.controls
# Your code here

Hint

Create the marker and control objects, set the frame and name, then add the control to the marker's controls list.

3

Implement the feedback callback for marker movement

Define a function called process_feedback that takes a single argument feedback. Inside the function, extract the marker's pose from feedback.pose and store it in a variable named pose. Then, call server.applyChanges() after processing feedback.

ROS

# Define process_feedback function to handle marker movement feedback
# Extract pose from feedback.pose
# Call server.applyChanges() after processing
# Your code here

Hint

Define the callback function to get the pose from feedback and call server.applyChanges() to update the marker server.

4

Insert the interactive marker and start the server

Insert int_marker into server with the feedback callback set to process_feedback. Then call server.applyChanges() to finalize the setup.

ROS

# Insert int_marker into server with process_feedback callback
# Call server.applyChanges() to start
# Your code here

Hint

Use server.insert() with the marker and callback, then call server.applyChanges() to activate.

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