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I'm wondering if tf is capable of providing the pose (position and orientation) of the last frame in the tree relative to the base frame in the same tree? Also, does tf use Denavit Hartenberg to establish the forward kinematic tree?


Originally posted by CroCo on ROS Answers with karma: 155 on 2022-05-29

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I'm not sure what you mean with 'the last'. With a lot of tf trees, there is not 1 last link.

As for getting the pose of the link relative to the base_link, that's what tf listeners are for. The tutorials:

  1. tf listener C++
  2. tf listener Python
  3. tf2 listener C++
  4. tf2 listener Python

Originally posted by Joe28965 with karma: 1124 on 2022-05-30

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By this question and its replies there: https://answers.ros.org/question/300789/denavit-hartenberg-dh-to-urdfsdf-or-tf-tf2/ I assume no standard DH for this forward kinematic, but it's not so sure.

You may find KDL documentation useful for this kind of calculations: http://wiki.ros.org/kdl and https://www.orocos.org/kdl.html

What can I use KDL for?

  1. 3D frame and vector transformations: KDL includes excellent support to work with vectors, points, frame transformations, etc. You can calculate a vector product, transform a point into a different reference frame, or even change the reference point of a 6d twist. For more information take a look at the geometry documentation on the KDL homepage.

  2. Kinematics and Dynamics of kinematic chains: You can represent a kinematic chain by a KDL Chain object, and use KDL solvers to compute anything from forward position kinematics, to inverse dynamics. For more information take a look at the chain documentation on the KDL homepage.The kdl_parser includes support to construct a KDL chain from a XML Robot Description Format (URDF) file.

  3. Kinematics of kinematic trees: You can represent a kinematic chain by a KDL Chain object, and use KDL solvers to compute forward position kinematics. Currently no other solvers are provided.


Originally posted by ljaniec with karma: 3064 on 2022-05-29

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