11.5.4. ROS/gscam

11.5.4.1. Introduction

gscam is a ROS node using the gstreamer library. The gstreamer library supports a few frame grabbers including the Hauppage one. The gstreamer development library can be installed using apt-get install. Make sure you install gstreamer 1.0, not 0.1.

ROS Ubuntu packages vs build from source

Use apt install to install gscam on Ubuntu 18.04 with ROS 1. The package name should be ros-melodic-gscam. It will install all the required dependencies for you. gscam is also available as a Debian package for ROS2 Galactic, Humble… so use apt intall for all ROS2 configuration.

On Ubuntu 20.04 gscam binaries for ROS 1 Noetic are not available via apt, so you will need to compile it in your ROS workspace. The original source code is on GitHub: https://github.com/ros-drivers/gscam. But you need a different version which can be found using the pull request for Noetic devel. So you need to clone https://github.com/hap1961/gscam in your catkin_ws/src. Then make sure you switch to the Noetic branch: cd ~/catkin_ws/src/gscam; git checkout noetic-devel. Finally, do catkin build. This info is from June 2022, it might need to be updated.

Using gscam

To start the gscam node, we provide a couple of ROS launch scripts. Make sure the launch script has been updated to use a working gstreamer pipeline (as described above using gst-launch-1.01). The main difference is that your pipeline for gscam should end with videoconvert and you need to remove autovideosink.

For a stereo system with the Decklink frame grabbers, use:

ros2 launch dvrk_video gscam_decklink_stereo.launch.py stereo_rig_name:=jhu_daVinci

Where jhu_daVinci is a name you want to give to your camera rig. This name will be used to define the ROS namespace for all the data published. The left/right camera outputs are available via the ROS topics:

  • /jhu_daVinci/left/image_raw

  • /jhu_daVinci/right/image_raw

For a system with a DeckLink Duo, the gscam_config in a launch script would look like:

<param name="gscam_config" value="decklinkvideosrc connection=sdi device-number=0 ! videoconvert"/>

11.5.4.2. (rqt_)image_view

One can use the image_view node to visualize a single image:

ros2 run image_view image_view image:=/jhu_daVinci/right/image_raw

If you prefer GUI, you can use rqt_image_view, a simple program to view the different camera topics. Pick the image to display using the drop-down menu in the top left corner.

11.5.4.3. dVRK launch files

At that point, we assume most groups are using SDI frame grabbers and the stereo display is using two images. The following launch files will start the frame grabbers using gscam, so one can collect the images over ROS and create 2 windows (left and right views) that can be used in your stereo display (drag and drop). The launch files are in dvrk_video and are provided for both ROS1 (XML) and ROS2 (Python).

  • decklink_stereo_1280x1024.launch: launches 2 gscam nodes to grab the video and de-interlace it as well as two ROS image viewers that can be dragged on the HRSV

  • decklink_stereo_goovis.launch: launches 2 gscam nodes to grab the video, de-interlace and start 2 OpenGL based windows that can be dragged on the stereo display. The main advantage of the OpenGL views are:

    • Low latency since there is no ROS message passing involved

    • Ability to change aspect ratio (e.g. with Goovis HMD)