Only released in EOL distros:  

System Dependencies

ar_recog requires the libgstreamer0.10-dev system dependency.

Making

rosmake ar_recog

The ar_recog package downloads and compiles the ARToolkit. It must therefore be able to connect to Sourceforge on the internet. This also accounts for why this step takes rather longer than many compilations. ARToolkit will only be downloaded once, with the locally cached version used thereafter.

Running

To run code that listens to /image messages:

rosrun ar_recog ar_recog

To run code for a specific image message such as one from gscam:

rosrun ar_recog ar_recog image:=/gscam/image

Messages and Services

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ar_recog publishes two messages tags contains the ar_recog/Tags message, the information about the found tags

ar/image contains the image with the tags outlined in the image

If the camera image is a rectified one with appropriate camera parameters, ar_recog will use them to determine the mapping between image space and physical space. However, the rectification pipeline is slow and camera calibration brittle, so the package also provides distance mapping with uncalibrated images. To use this feature, it must know your camera's horizontal angle of view. This can be provided as a ROS parameter (aov), or determined using the ar_recog/CalibrateDistance service.

Calibrating Distance

This is only necessary when not using a calibrated camera.

  • Set up a clear, recognized AR tag at a known distance from the camera.
  • Start the ar_recog node and monitor the /tags message

  • Arrange the AR tag and camera so that the tag coordinates are as close as possible to the center of the image, and the xRot, yRot and zRot are as close as possible to zero. This will minimize distortion.
  • Call the ar_recog/CalibrateDistance service, where dist is the distance between the AR tag and the camera in millimeters:

rosservice call ar/calibrate_distance dist

Tips

  • The more accurately the distance is known, the better ar_recog is able to undistort the image. Thus you may have to repeat the service call a few times until the reported distance converges on the value you are providing.

  • Save this aov value to provide as a ROS parameter next time you use ar_recog with this camera.

ARToolKit Compatibility/Interoperability

ar_recog is compatible with standard ARToolKit pattern and object_data files. When not used with ROS' image_proc, ar_recog utilizes an ARToolkit camera_para.dat file. See the files within the bin directory and the ARToolKit documentation.

Wiki: ar_recog (last edited 2010-06-02 18:45:26 by KenConley)