Visualization & Debugging

Overview

Visualization and debugging tools are essential for understanding robot behavior, validating sensor data, and diagnosing issues during development.
This section introduces the primary tools used with Pixel Robot to visualize data and debug the ROS 2 system.

The main tools covered are:

  • RViz2
  • rqt tools
  • ROS 2 command-line utilities

RViz2 Overview

RVIZ Logo

RViz2 is the primary visualization tool used to view the robot’s state, sensor data, and navigation information.

With RViz2, you can visualize:

  • Robot model (URDF)
  • Coordinate frames (TF)
  • Laser scan data
  • Odometry
  • Maps
  • Navigation goals and paths

RViz2 is typically launched automatically during robot bringup.

RViz2 Configuration

Fixed Frame

Fixed Frame

Ensure the Fixed Frame is set correctly:

  • Recommended: odom (or map when mapping/localization is active)

Incorrect fixed frames are a common source of visualization issues.

Common RViz Displays

Recommended displays to enable:

  • RobotModel – Shows the robot URDF
  • TF – Visualizes coordinate frames
  • LaserScan – Displays LIDAR data
  • Odometry – Visualizes robot motion
  • Map – Shows generated or loaded maps
  • Path – Displays navigation paths

Verifying Sensor Data

LIDAR Visualization

Laserscan

  • Add a LaserScan display
  • Topic: /scan
  • Verify that obstacles appear correctly around the robot
  • Ensure scan rotates with the robot frame

Camera Visualization (V3)

Image

  • Add an Image display
  • Topic:
  • V2: /camera/image_raw
  • V3: /camera/color/image_raw
  • Confirm image stream updates in real time

TF Debugging

TF (transform) errors are one of the most common issues in ROS-based systems.

Visualizing TF Frames

Enable the TF display in RViz2 to:

  • Verify correct frame hierarchy
  • Check transform directions
  • Identify missing or misaligned frames

Common frames include:

  • map
  • odom
  • base_link
  • laser
  • camera_link

Generating TF Tree

ros2 run tf2_tools view_frames

TF

This generates a PDF showing the complete TF tree.

Odometry Debugging

Checking Odometry Topic

ros2 topic echo /odom

Odom

Verify that:

  • Position updates when the robot moves
  • Orientation changes during rotation
  • No sudden jumps or drift at standstill

Visualizing Odometry

  • Add Odometry display in RViz2
  • Check smooth motion and correct orientation
  • Verify odom frame alignment

odometry

rqt Tools

rqt provides GUI-based debugging and introspection tools.

rqt_graph

rqt_graph

rqt

  • Visualizes node and topic connections
  • Useful for verifying data flow
  • Helps detect missing or misconnected nodes

rqt_plot

rqt_plot
  • Plot values over time
  • Useful for:
  • Odometry velocity
  • Encoder-derived data
  • Sensor readings

rqt_console

rqt_console
  • Displays ROS 2 log messages
  • Filter logs by severity and node
  • Useful for runtime error detection

Command-Line Debugging Tools

List Nodes

ros2 node list

Inspect Node Info

ros2 node info <node_name>

Topic Frequency

ros2 topic hz /scan
ros2 topic hz /odom

Ensures data is being published at expected rates.

Common Debugging Scenarios

Issue Debugging Step
Robot not moving Check /cmd_vel and serial node
No LIDAR data Check /scan topic and USB connection
Navigation fails Inspect costmaps and TF
Map drifting Check odometry accuracy
RViz empty Verify fixed frame and TF tree

Debugging Best Practices

  • Always check /tf first
  • Verify sensor topics before navigation
  • Use low speeds during testing
  • Debug one subsystem at a time
  • Keep RViz displays minimal to improve performance

With proper visualization and debugging, diagnosing robot issues becomes significantly easier 🚀