How to plot position(x y z) and velocity of fixed frames(end-effector) in rqt?

Question

hi . i need answer to complete my Master's thesis. i want plot position and velocity of end effector that have fixed joint using rqt. How to plot position(x y z) and velocity of fixed frames(end-effector) in rqt ?? can you write a very very very simple examlpe for that ?? like two link and one joint arm . and plot position(x y z) of second link in rqt ??

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Originally posted by zakizadeh on ROS Answers with karma: 217 on 2017-01-21

Post score: 1

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Original comments

Comment by NEngelhard on 2017-04-13:
Please stop editing your question just to put it back on the first page.

Comment by zakizadeh on 2017-04-13:
can you write a very very very simple examlpe for that ?? for god doing that , please !

Comment by NEngelhard on 2017-04-13:
You don't show that you tried to do it yourself, you don't even care about writing correctly. Why should someone else do your work?

Comment by zakizadeh on 2017-04-13:
i tried . but i just need examlpe for that . i cant find any sample , like two link and one joint arm . and plot position(x y z) of second link in rqt

Comment by NEngelhard on 2017-04-13:
You were told how to do it several times: get a tf client, use it to get your translation, publish your values on separate float-topics.

Answer 1

A fixed joint has no element in the /joint_states/position array, as it cannot change from 0.0 (it's fixed, after all).

You could probably use the pose of your EEF as tracked by TF. Something like rosrun tf tf_echo CHAIN_START CHAIN_END (where CHAIN_START could be base_link and CHAIN_END the frame that represents your EEF) should give you the transform.

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Edit:

how can i plot velocity of fixed joint ??

There is no entry in any of the arrays in a JointState message for fixed joints. Again: they are fixed. No velocity, acceleration or effort for these joints.

Note: I'm describing the typical situation (such as with joint_state_publisher with gui:=true). Whether all drivers do the same thing I cannot say, but it wouldn't make sense to me to publish joint values for something like a fixed joint.

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Originally posted by gvdhoorn with karma: 86574 on 2017-01-21

This answer was ACCEPTED on the original site

Post score: 2

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Original comments

Comment by zakizadeh on 2017-01-21:
how can i plot pose for my fixed joint(joint_U26_1) like rqt_plot /turtle1/pose/x:y ??

what is a turtle1 ??

Comment by gvdhoorn on 2017-01-22:
Joints don't have poses, only links have poses (every link becomes a TF frame). Plotting TF frames is slightly involved. See #q58793 for some hints.

Comment by gvdhoorn on 2017-01-22:
Some other options:

• tf_trajectory
• hector_trajectory_server

Comment by zakizadeh on 2017-01-22:
how use this command ?? rxplot /tf/transforms[0]/transform/translation/x thats not working .

Comment by gvdhoorn on 2017-01-22:
rxplot is now rqt_plot.

Comment by zakizadeh on 2017-01-22:
rqt_plot /tf/transforms[0]/transform/translation/x not working .

can i use this page?? what can i do ?

Comment by zakizadeh on 2017-01-23:
what about this one??

Comment by gvdhoorn on 2017-01-23:
That page still works with JointState messages, which do not typically include fixed joints. You'll have to plot TF frames, not JointState msgs. The pkgs I linked in my earlier comment could help you with that.

Comment by zakizadeh on 2017-01-23:
can you write a very simple sample for that ?? i want plot pose ( x and y and z ) of link

Comment by zakizadeh on 2017-01-23:
in #q58793 wrote i shoud use pose topic parsed from the node tf . how can i do that? i cant found any sample .

Comment by gvdhoorn on 2017-01-24:
Other than tf_trajectory and hector_trajectory_server, I don't know of any existing pkgs/nodes that can do what you want, but in a nutshell:

1. create a TF listener for the TF frame you want to plot
2. convert the TF to a geometry_msgs/Pose and publish that
3. plot

Comment by zakizadeh on 2017-01-24:
im sorry . can i plot in RViz or rqt_plot ?? which one ??

Comment by gvdhoorn on 2017-01-25:
TF frames you can show in RViz (using either the TF Display or one of the pkgs I linked above). If you create the TF -> geometry_msgs/Pose converter, you can use RQT to plot the individual members of the Pose msg.

Comment by zakizadeh on 2017-01-27:
i need practical example .