Ubuntu Linux for Robotics · Lesson 67 of 96

Point cloud processing (PCL)

Installing PCL, the pcl_ros tools, filtering clouds and viewing them in RViz2.

Estimated time · 60–90 min

Learning goals

What you will understand

Explain point cloud processing (pcl) in your own words
Use it in a small workstation example
Verify the result instead of assuming it worked

Understand the idea first

The mental model

The Point Cloud Library (PCL) processes 3D data. Install the development files with sudo apt install libpcl-dev and the ROS integration with ros-lyrical-pcl-ros and ros-lyrical-pcl-conversions. In C++, convert a PointCloud2 with pcl::fromROSMsg, filter it, and convert back.

Build steps in order: downsample (VoxelGrid) to cut the point count, crop to the region of interest (PassThrough), then remove the floor or cluster objects. Check the results in RViz2 with the PointCloud2 display, and measure how long each step takes with the ros2 topic delay tool or your own timers.

Guided lesson

Work through these steps

1.
Open a terminal and record the current state before changing anything.
2.
Read the point cloud processing (pcl) commands and predict what each one does.
3.
Run the commands one at a time and compare each output with your prediction.
4.
Write the commands that worked in a setup note you can repeat later.

Worked example

Read it before you run it

sudo apt install libpcl-dev ros-lyrical-pcl-ros ros-lyrical-pcl-conversions
# Install PCL and its ROS bridges.
ros2 topic list -t | grep PointCloud2
# Find point cloud topics.
ros2 topic hz /points
# Measure the cloud rate.
ros2 topic bw /points
# Measure how much bandwidth the raw cloud needs.
ros2 run pcl_ros pcd_to_pointcloud room.pcd --ros-args -p publishing_period_ms:=1000
# Publish a saved cloud for testing.

What the example is doing

1.Lines without sudo only inspect or change files you own; sudo authorizes a system-wide change.
2.Read command output before moving to the next line. Stop if names, versions, disks, or paths differ from the lesson.
3.Comments beginning with # explain safety checks and are not executed by the shell.

Watch it run · Sensor view

See what this code does

The terminal types this lesson's practice solution and runs it. The scene shows the kind of robot behaviour that code drives. It plays by itself and loops.

Practice code

Now type it yourself

Open a terminal, run the starter line by line (or save it as practice.sh and run bash practice.sh), and replace every TODO with your own command.

# TODO: measure the bandwidth of the /points topic

Expected output

The bandwidth of the point cloud topic

Stuck? Show the full solution (try it yourself first)

ros2 topic bw /points

Expected result

How you know it worked

Each command completes without an unexplained error.
Your notes contain the command, the important output, and what it proves.

Practical exercise

Apply the lesson

Publish a saved cloud, write a node that downsamples it with a 5 cm voxel grid, and compare the point count and bandwidth before and after.

Before you continue

You recorded the starting state
Every command and output is understood
The change can be repeated from your notes

If something goes wrong

A command says permission denied.

Check ownership and permissions first. Do not add sudo unless the command changes a documented system location.

A command or package is not found.

Check spelling, Ubuntu version, enabled repositories, and whether the previous installation command succeeded.