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Overview

gscam is meant as a simple approach to using a webcam in ROS that maximizes compatibility. gscam leverages Gstreamer, a multimedia framework similar to DirectShow. Specifically: Gstreamer can be used to build up multimedia "pipelines" consisting of sources, sinks, and filters. For example: a v4l webcam source might be filtered by an upscaler before being sent to the screen (a sink). Alternately, a mp4 file might act as a source and be filtered into an avi file as a sink. There are many possibilities. For an overview see: Using Gstreamer.

gscam can attach itself to a specially formatted pipeline. Provided this pipeline is processing RGB video, gscam will rebroadcast the video over as both a standard ROS image transport and a ROS Camera. Since Gstreamer is compatibile with almost every video capture standard under Linux (and many on OSX), gscam makes ROS defacto compatible with almost every Linux webcam or video system available. Moreover, because there are a number of Gstreamer filters for processing video (e.g. white-balancing, cropping, etc.) gscam allows for a more advanced video processing even with cheaper webcams.

Gstreamer is an extremely rich framework, but basic usage is fairly simple. Please see the "Basic Usage" section to get started. You may also find the Gstreamer documentation on their website to be helpful.

Running

gscam expects an environmental variable, GSCAM_CONFIG, to contain a gstreamer pipeline definition for it to launch. There is one important restriction:

• At the end of the pipeline where gscam will attach itself, the pipeline must be carrying RGB formatted video.

Here's an example launch that should work on almost any machine where Gstreamer is installed and a camera of some kind is available attached to /dev/video2. Note that gscam expects to start within the bin directory:

roscd gscam
cd bin
export GSCAM_CONFIG="v4l2src device=/dev/video2 ! video/x-raw-rgb,framerate=30/1 ! ffmpegcolorspace"
rosrun gscam gscam

If you see a message about a "failure to PAUSE" or something similar, the most likely cause is a permission issue with the available video devices.

If you see a "Processing..." message, it means gscam is happily publishing.

You can graphically explore many of the available video devices with the gstreamer-properties utility. gst-inspect-0.10 (or .09 or whatever is your Gstreamer version number) will list all of the available plugins. For more help on specifying the GSCAM_CONFIG, see this cheatsheet.

Advanced Usage

gscam is fully compatible with the ROS Camera interface and can be calibrated to provided rectified images. For details, see the appropriate ROS documentation on the image_pipeline wiki page.

An example launch file which includes loading calibration data is

<launch>
  <!-- Set this to your camera's name -->
  <arg name="cam_name" value="creative_cam" />

  <!-- Start the GSCAM node -->
  <env name="GSCAM_CONFIG" value="v4l2src device=/dev/video0 ! video/x-raw-yuv,framerate=30/1,width=640,height=480 ! ffmpegcolorspace " />
  <node pkg="gscam" type="gscam" name="$(arg cam_name)">
    <param name="camera_name" value="$(arg cam_name)" />
    <param name="camera_info_url" value="package://localcam/calibrations/${NAME}.yaml" />
    <remap from="camera/image_raw" to="$(arg cam_name)/image_raw" />
  </node>

  <!-- Provide rectification -->
  <node pkg="image_proc" type="image_proc" name="creative_image_proc"
        ns="$(arg cam_name)" />

  <!-- View the raw and rectified output -->
  <node pkg="image_view" type="image_view" name="creative_view" >
    <remap from="image" to="/$(arg cam_name)/image_raw" />
  </node>
    
  <node pkg="image_view" type="image_view" name="creative_view_rect" >
    <remap from="image" to="/$(arg cam_name)/image_rect_color" />
  </node>
</launch>

Note it assumes calibration data is stored in a subdirectory of the ROS package 'localcam'.

ROS API

gscam

Sets up a ROS camera interface for a gstreamer-based camera.

Published Topics

image_raw (sensor_msgs/Image)

• The unprocessed image data.

camera_info (sensor_msgs/CameraInfo)

• Contains the camera calibration (if calibrated) and extra data about the camera configuration.

Services

set_camera_info (sensor_msgs/SetCameraInfo)

• Set the appropriate camera info (TF frame, calibration parameters, ROI etc.)

Troubleshooting

Bad Camera Info

MessageFilter [target=/map ]: Discarding message from [/gscam_publisher] due to empty frame_id.  This message will only print once.

You need to set the TF frame via the set_camera_info service described above.