Implementing sensor fusion using the ROS

Implementing sensor fusion using the ROS robot_pose_ekf package. You will simulate a TurtleBot, collect data from its sensors, fuse the measurements using an Extended Kalman Filter (EKF), and visualize the estimated trajectory in RViz.

1. The five ROS packages and their roles

1. turtlebot_gazebo

Launches the simulated TurtleBot in a Gazebo environment. The robot generates simulated sensor data and odometry as it moves.

2. robot_pose_ekf

Fuses odometry, IMU, and visual odometry measurements to estimate the robot's position and orientation.

3. odom_to_trajectory

Converts odometry messages over time into a trajectory path for visualization, assuming the lab's implementation provides this functionality.

4. turtlebot_teleop

Allows you to control the robot using keyboard commands.

5. rviz

Visualizes the robot's estimated pose, coordinate frames, odometry, and trajectory.

2. How the ROS nodes work together

Gazebo + TurtleBot

Simulated robot and sensor data

ROS topics

Wheel odometry · IMU · Visual odometry, if available

robot_pose_ekf

Sensor fusion and pose estimation

Trajectory node

RViz

Teleoperation provides the velocity commands that move the robot. Gazebo simulates the resulting motion, and the ROS nodes process and display the resulting estimates.

Note that the exact topic names and connections depend on the lab's ROS distribution and package configuration.

3. Discover the ROS topics

Before integrating the packages, inspect the available topics and their message types.

For a ROS 1 lab, useful commands include:

# List active topics
rostopic list

# Inspect a topic's message type and publishers
rostopic info /odom

# Examine live odometry data
rostopic echo /odom

# Inspect the available nodes
rosnode list

Look for topics carrying:

• nav_msgs/Odometry — wheel or visual odometry.

• sensor_msgs/Imu — inertial measurements.

• geometry_msgs/Twist — velocity commands for teleoperation.

• geometry_msgs/PoseWithCovarianceStamped — pose estimates with uncertainty.

The names above are examples, not a guarantee that your simulator publishes every message.

4. Create a single launch file

A ROS launch file allows you to start the simulation, EKF, trajectory conversion, and RViz with one command.

A simplified ROS 1 example is:

<launch>
  <!-- Launch the simulated robot -->
  <include file="$(find turtlebot_gazebo)/launch/turtlebot_world.launch" />

  <!-- Start the EKF node -->
  <node pkg="robot_pose_ekf"
        type="robot_pose_ekf"
        name="robot_pose_ekf"
        output="screen" />

  <!-- Add the lab's trajectory conversion node here -->

  <!-- Start RViz -->
  <node pkg="rviz"
        type="rviz"
        name="rviz"
        output="screen" />
</launch>

This is a template, not a verified drop-in launch file. The Gazebo launch filename, EKF configuration, trajectory node executable, and topic remappings must match your installed packages. Teleoperation can be started separately in another terminal or added to the launch file if its configuration supports that.

Once configured, the project can be started with:

roslaunch <your_package> <your_launch_file>.launch

5. What you should verify at the end

• Gazebo launches the TurtleBot successfully.

• Keyboard commands move the robot.

• The EKF receives the sensor measurements it expects.

• The EKF publishes a pose estimate.

• The trajectory node converts the relevant odometry into a path.

• RViz displays the robot pose and trajectory correctly.

• All required nodes can be started using one launch command.

One important compatibility note: robot_pose_ekf is a ROS 1 package commonly associated with older TurtleBot workflows. Its supported inputs and configuration differ from newer ROS 2 localization tools, such as robot_localization. Also, the EKF can only fuse measurements that are actually published and correctly configured; having a camera in the simulation does not automatically mean visual odometry is available.