Workshop 11 ‐ Object counting

Preliminaries

First, synchronise your fork with the main repository on GitHub (Sync fork) as some structural changes were made and new files were added. Then clone or pull the repository to your local PC and re-open it in the dev container using VSC. Rebuild the updated packages colcon build --symlink-install, and source the workspace source install/setup.bash.

Task 1 - Object counting in 3D

The repository contains a new node counter_3d.py demonstrating how to count the detected objects in global coordinates with a simple filter preventing double counting. The node subscribes to object_location topic and keeps track of all detected objects. The new detection is first checked for its distance to all counted objects so far and if it is detected close to the existing object (distance below detection_threshold), then it is ignored. This allows the robot to detect the objects from multiple viewpoints without registering multiple counts.

• To see how the counter works, launch the simulator with the default environment: ros2 launch limo_gazebosim limo_gazebo_diff.launch.py.
• Insert a number of small red objects in Gazebo and place them around the robot so that not all of them are immediately visible. You might need to move the robot and the objects manually into a location with more free space around. Remember that you can copy and paste one object to avoid editing multiple objects.
• Run the detector node by issuing ros2 run rob2002_tutorial detector_3d. This time, the detector is not visualising the image processing steps to reduce processing delays but you can change that by setting visualisation=True if required.
• Run the counter node by issuing ros2 run rob2002_tutorial counter_3d. The node prints out a full list of all objects in the terminal.
• You can also visualise the counted objects in rviz. Run rviz, change Fixed Frame to odom, add Robot Model with Description Topic /robot_description and then Add/By topic /object_count_array. You should see arrows indicating the location of individual objects.

Task 2 - Counting and moving

The new counter allows the robot to register objects from different viewpoints.

• Run the keyboard teleoperation node ros2 run teleop_twist_keyboard teleop_twist_keyboard and slowly move the robot around so that you register also those objects which were outside of the robot's field of view.
• The counter's key parameter is detection_threshold. Set that to different values and note its behaviour with different robot speeds and object sizes.

Task 3 - Real robot

• Try the counter on the real robot with real colour objects. You will need to set the real_robot variable in the detector to True and adjust the ranges of the colour filters. Try it out with the odometry first and then use the map-based navigation.