Webcam docker

This docker file can be used to setup automatically webcams and make them publish topics on ROS2 Humble.

1. Build docker

Digit the following command (in the folder where Dockerfile is located) to create the docker image:

docker build -t webcam_ros2 .

2. Access container

From the same folder, digit the following command:

./docker_run.sh

3. Start webcams

List video devices:

v4l2-ctl --list-devices

Get info about video devices:

v4l2-ctl --list-formats-ext -d /dev/video9

Get real stream frequency:

v4l2-ctl --device=/dev/video9 --stream-mmap --stream-count=100

Once inside the container, you can start your ROS2 node by launching multiple webcam publishers:

ros2 launch launcher_pkg launch_file.py \
    video_device1:=/dev/video6 \
    video_device2:=/dev/video10 \
    video_device3:=/dev/video14 \
    image_width:=640 \
    image_height:=480 \
    framerate:=30 \
    transport_on:=false

Note: This command must be modified based on the number of webcams and based on the device port numbers (v4l2-ctl --list-devices).

Since the webcame node publishes compressed PNG images, I need transport node to convert them in Image type to display on RVIz. This is done by enabling ''transport_on:=true'' in the roslaunch command.

Otherwise, from terminal:

ros2 run image_transport republish compressed raw \
    --ros-args -r in/compressed:=/webcam1/image_raw \
               -r out:=/webcam1/image_raw/compressed

To visualize:

ros2 run rqt_image_view rqt_image_view

Docker deep dive

It is a tool to package and run software in isolated environments.

• Image: a snapshot of a filesystem + instructions for running. You build images with docker build.
• Container: a running instance of an image. You create/run containers from an image.

1. Dockerfile

# Use official ROS2 Humble base image
FROM ros:humble-ros-base

# Install dependencies
RUN apt-get update && apt-get install -y \
    python3-pip \
    python3-opencv \
    ros-humble-cv-bridge \
	ros-humble-image-transport \
    ros-humble-compressed-image-transport \
 && rm -rf /var/lib/apt/lists/*

# Copy your ROS2 workspace into container
COPY ros2_ws_webcam /ros2_ws_webcam

# Build the workspace
WORKDIR /ros2_ws_webcam
RUN . /opt/ros/humble/setup.sh && colcon build

# Source ROS2 and workspace
SHELL ["/bin/bash", "-c"]
RUN echo "source /opt/ros/humble/setup.bash" >> ~/.bashrc
RUN echo "source /ros2_ws_webcam/install/setup.bash" >> ~/.bashrc

2. Build docker image

From folder where you have Dockerfile:

docker build -t webcam_ros2 .

• -t: webcam_ros2: gives a name to the image (you can choose whatever you want)
• .:means the Dockerfile is in the current directory

This step copies your workspace ros2_ws_webcam into the container, installs dependencies, and builds the workspace with colcon build.

2.1 Bind mount of your local workspace

If the code is copied inside the image (COPY ros2_ws_webcam /ros2_ws_webcam), every time you change a line you need to rebuild the image.

Solution: remove COPY from the Dockerfile and just mount the local folder with the docker run command:

docker run --rm -it \
  -v ~/Documents/Coding/ros2_ws_webcam:/ros2_ws_webcam \
  webcam_ros2 \

Inside the container you will see the same folder from your host (/ros2_ws_webcam).

You can edit from your PC with VSCode, then inside the container just run:

cd /ros2_ws_webcam
colcon build
source install/setup.bash
ros2 run webcam_pkg webcam_node

Now you do not have to rebuild image every time you modify the code.

2.2 Images info & delete

To see images:

docker image ls

To see containers:

docker ps -a

To delete images:

docker rmi <image_id_or_name>

To delete containers:

docker rm -f <container_id_or_name>  # force cancellation
docker container prune # delete all unused containers

3. Docker run

Start the container launching the following command (from any folder):

bash docker_run.sh

3.1 Exit from a running container

To exit running container, just digit:

exit

3.2 Docker run via script bash

Create script bash file:

touch docker_run.sh

Inside it you should put the docker run command with all the required settings (device, network host, etc).

Make the file executable:

chmod +x docker_run.sh

After that you can launch it with:

./docker_run.sh