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How do I specify in the URDF file format how the root link of a robot is connected to the world? The root link of the robot could either be free floating in the world or it could be fixed. E.g. for a PR2 the root link should be free floating as the robot should be able to move around. In contrast, a robot arm is usually bolted into something and thus the root link is fixed.

EDIT:

I'll try to make more clear what I am trying to achieve. I am not trying to implement anything in ROS. Thus, a publisher or node is not going to help me. I am trying to load a URDF model into our own simulator and I am trying to understand the URDF file format. A dynamics simulator needs to know whether a robot root link is attached rigidly to the world or free floating. I am not sure exactly how gazebo does this.


Originally posted by Tobias Kunz on ROS Answers with karma: 3 on 2013-01-24

Post score: 0

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2 Answers 2

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There is no way to specify what a URDF model's relationship to the world is. You can

A) Include part of the world as part of the URDF, thus specifying the relationship with a joint, as you would any other part.

B) Add some custom field to the URDF to specify such, although such a feature would most likely not be natively supported by the URDF standard.

C) Specify the relationship some other way.


Originally posted by David Lu with karma: 10932 on 2013-01-25

This answer was ACCEPTED on the original site

Post score: 2

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It is not directly specified by the model (the robot motion w.r.t the world may vary depending on your application). However, an external node usually provides the "base_link" to "world" frame (or other global frames, see REP 105). If you have a fixed manipulator then a static_transform_publisher is enough but if you have a mobile robot then you need a localization node that will estimate the robot motion.


Originally posted by Thomas with karma: 4478 on 2013-01-24

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Original comments

Comment by Andromeda on 2014-08-28:
Hi Thomas, could you please better explain what you mean with "localization node"? I have the same problem as Tobias but to me is not clear how to create a localizatione node nor how to implement it. Thank you

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