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Inverse Kinematics on rviz

asked 2018-08-23 08:38:10 -0600

tony chen gravatar image


I am recently working on Fetch robot and motion planning and I have run into such a problem:

Given a serial of pose in work space, the serial of configurations in joint space the IK solver output are not continue (sometime flip).

I have noticed that when you are dragging the interactive marker on the end-effector in rviz, the joints can always be continue. Does anyone have any idea what kind of IK algorithm rviz is using?


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answered 2018-08-23 15:49:53 -0600

fergs gravatar image

RVIZ doesn't have any IK internally -- I presume you are using the MoveIt configuration to drag the arm with Interactive Markers? If so, the IK is probably the KDL plugin from MoveIt. Just a note though: it does not provide any guarantee that the arm won't "flip" -- you're probably just getting lucky since the Fetch has so many continuous rotation joints.

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Thank you very much for your help!

tony chen gravatar image tony chen  ( 2018-08-25 20:15:40 -0600 )edit

Tony, if that answers your question, please click the checkmark next to my answer to accept the answer.

fergs gravatar image fergs  ( 2018-08-25 22:50:12 -0600 )edit

Hi fergs, sorry for asking you again. Do you know any IK plugin in Moveit that can guarantee the continuity of the joint angles? Thanks!

tony chen gravatar image tony chen  ( 2018-08-27 06:13:43 -0600 )edit

There really isn't one AFAIK -- that's still an area of active research (for instance, see )

fergs gravatar image fergs  ( 2018-08-27 10:24:01 -0600 )edit

No guarantee, but trac_ik configured with Distance solve type will generally return solutions that are "close" to the current pose of the robot. It doesn't give any guarantees, but it will try.

Edit: that is not the same as 'continuity' of course.

gvdhoorn gravatar image gvdhoorn  ( 2018-08-27 10:32:45 -0600 )edit

how can we get that angles

omeranar1 gravatar image omeranar1  ( 2021-02-23 09:27:37 -0600 )edit

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Asked: 2018-08-23 08:38:10 -0600

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Last updated: Aug 23 '18