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I found weird things.

I open rviz for PR2.

image description

We can see that in /base_link, z axis is blue.

But why left arm joint axis is not blue but green?

Is PR2 follow DH convention?

If not, how to understand the coordinate design of PR2?

Thank you~


Originally posted by sam on ROS Answers with karma: 2570 on 2014-11-04

Post score: 0

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2 Answers 2

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Robots using URDF rarely follow DH conventions -- and a number or ROS packages (calibration, for sure) don't necessarily work with all the extra fixed rotations that are needed to make URDF follow DH.

For the PR2, and a number of other robots, the convention has been that "when the joints are at their 0.0 position, all of the TF frames will line up parallel to the base_link orientation". Thus, if you put the PR2 arm out forward and level with the ground, with all the roll joints zeroed, all the links will be red (X) forward, blue (Z) up.


Originally posted by fergs with karma: 13902 on 2014-11-09

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The URDF allows you to freely set the axis of rotation for a joint.

The coordinate frames are probably layout so that coordinates on a link are as intuitive as possible.


Originally posted by dornhege with karma: 31395 on 2014-11-04

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