Camera Publisher

A image from camera or video file and a camera info publisher node for ROS2.

Features

• Works with USB cameras that are recognized by V4L2 and also IP cameras.
• It is also possible to publish frames of a video file.
• Undistortion of frames according to calibration data.
• Importing necessary configuration file generated by camera_calibrator node
• Additional parameters are stored in Launch File

ROS Topics

Publishers

Topic Name	Message Type
camera/image_color	CompressedImage
camera/image_undist_color	CompressedImage
camera/camera_info	CameraInfo

Getting Started

Dependencies

• OpenCV
  To install:

  $ python3 -m pip install opencv-python

• PyYAML
  To install:

  $ python3 -m pip install pyyaml

  When you run the node, if you still get an error about PyYAML, check its version

  $ python3
  > import yaml
  > yaml.__version__

  If it is smaller than 5.1, you should update it

  $ python3 -m pip install -U pyyaml

• CvBridge
  To install:

  $ sudo apt install ros-eloquent-cv-bridge

Installation

1. Clone repository to /your_workspace/src

   $ git clone https://git.fh-aachen.de/kurhan/camera_rgb.git

2. Build /your_workspace with colcon

   $ colcon build

Usage

Launch File

It has only two parameters.

1. read_video is a boolean variable which set image acquisiton source either a camera or video file

   • If True then the node tries to read video file which is given in parameter video_path

   • If False then the node tries to open designated camera in configuration file.

2. video_path keeps the absolute path of desired video file, e.g. /home/<user>/Desktop/sample.mp4

How to Run Node

After setting all parameters in Launch File and configuration file properly then,

$ ros2 launch camera_rgb camera_rgb.launch.py

Imported Configuration file

The node imports a YAML file generated by camera_calibrator as a configuration file. This file contains matrices for calibration and some more additional parameters which are required.

• The name of the file must be camera.yaml and it must be in camera_calibration/config directory
• image_width and image_height set resolution of camera
• camera_source holds index number of camera. It is also possible to enter address of an IP Camera, e.g. http://192.168.0.123:5000/video
• camera_fps sets camera frame rate.
• camera_name is useful when there are multiple cameras on the system.
• camera_matrix is a unique result derived from calculations done on checkerboard and used for undistortion of captured frames. $f_x$ and $f_y$ are focal lengths and $c_x$ and $c_y$ are optical centers

$$camera~matrix = \begin{bmatrix} f_x & 0 & c_x\\\ 0 & f_y & c_y\\\ 0 & 0 & 1 \end{bmatrix}$$

• distortion_model is set to plumb bob by default. This model requires 1x5 distrotion matrix.
• distortion_coefficients contains 5 coefficients and used for undistortion of captured frames.

$$distortion~coefficients = \begin{bmatrix} k_1 & k_2 & p_1 & p_2 & k_3 \end{bmatrix}$$

For more info you can check OpenCV tutorial and documentation