In this lecture, the basics of TF and the actual functionality of the tf2_ros package will be explained.

tf2_ros package

• Implements functional aspects, and actively maintain relations.
• Transform pose: allows for “time travel” – look up the spatiotemporal relation.

Was there a TF (1) package?

• Yes
  • • Used in many applications
    • Command line tools
    • All in one (vs clear separation in TF2)
• All TF functionalities are migrated to tf2_ros
  • • Availability of a transform buffer in tf2_ros.

Information representation:

• Quantification
  • • 3D transformation.
    • ROS topic: /tf (tf2_msgs/TFMessage)

Command line tools:

• Print transformation
  $ rosrun tf tf_echo <source_frame> <target_frame>
• View the “TF tree”
  $ rosrun tf view_frames
  or
  $ rosrun rf2_tools view_frames.py
• Publish a static transform
  $ rosrun tf2_ros static_transform_publisher <trans> <rot> "parent" "child"
• tf_echo (static and dynamic)

tf_echo (static)

• Query transform that never moves in our environment.
• Prints latest information with 1Hz.
• Fixed with each other (equal times).
• Outputs translation and quaternion .