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How do we remap all of the input and ouput topics from a node in a systematic way?

asked 2020-05-31 10:44:46 -0500

Britsk gravatar image

updated 2020-05-31 21:10:13 -0500

The probIem I am facing is that I am using a package with the following launch file:

<launch>
        <node pkg="mypackage" type="task_A" name="task_A_node" output="screen">
        </node>

        <node pkg="mypackage" type="task_B" name="task_B_node" output="screen">
        </node>
</launch>

And when running rqt_graph, one will get the following graph:

/input -> /task_A_node -> {/internal_topic1, /internal_topic2}-> /task_B_node -> {/output1, /output2}

Here the topic names "/input", "/internal_topic1", "/internal_topic2", "/output_1", "/output_2" have been hardcoded in the program by the author of the package. There are actually a lot more topics so it's actually quite complicated to modify the code to parameterize the naming of the input/output topics.

Now that I want to run two instances of this program in paralel as black boxes, each with its own input like this:

<launch>
       <!-- group 1 -->
       <group>
           <node pkg="mypackage" type="task_A" name="task_A_node1" output="screen">
           </node>
           <node pkg="mypackage" type="task_B" name="task_B_node1" output="screen">
           </node>
      </group>

      <!-- group 2 -->
      <group>
           <node pkg="mypackage" type="task_A" name="task_A_node2" output="screen">
           </node>
           <node pkg="mypackage" type="task_B" name="task_B_node2" output="screen">
           </node>
      </group>
</launch>

Now the issue is taht if I don't remap the topics, the input and output of group 1 and group 2 will be mixed. So the way I was thinking to work around this is to remap all topics related to the each instance to the same name with a suffix, for example:

<launch>
       <!-- group 1 -->
       <group>
           <node pkg="mypackage" type="task_A" name="task_A_node1" output="screen">
               <remap from="/input" to="/input_group1">
               <remap from="/internal_topic1" to="/internal_topic1_group1">
               <remap from="/internal_topic2" to="/internal_topic2_group1">
           </node>

           <node pkg="mypackage" type="task_B" name="task_B_node1" output="screen">
               <remap from="/internal_topic1" to="/internal_topic1_group1">
               <remap from="/internal_topic2" to="/internal_topic2_group1">
               <remap from="/output1" to="/output1_group1">
               <remap from="/output2" to="/output2_group1">
           </node>
      </group>

      <!-- group 2 -->
      <group>
           <node pkg="mypackage" type="task_A" name="task_A_node2" output="screen">
               <remap from="/input" to="/input_group2">
               <remap from="/internal_topic1" to="/internal_topic1_group2">
               <remap from="/internal_topic2" to="/internal_topic2_group2">
           </node>
           <node pkg="mypackage" type="task_B" name="task_B_node2" output="screen">
               <remap from="/internal_topic1" to="/internal_topic1_group2">
               <remap from="/internal_topic2" to="/internal_topic2_group2">
               <remap from="/output1" to="/output1_group2">
               <remap from="/output2" to="/output2_group2">
           </node>
      </group>
</launch>

So I want to ask if there is anyway to quickly remap all topics that come in and out of a node to something with the same name but with a suffix MORE EFFECIENTLY, other than having to do that one by one like I did above?

Thanks!

Edit: clarifying the issue with examples.

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answered 2020-05-31 12:12:21 -0500

gvdhoorn gravatar image

updated 2020-05-31 12:49:51 -0500

So I want to ask if there is anyway to quickly remap all topics that come in and out of a node to something with the same name but with a suffix

It wouldn't be a suffix, but a prefix, but perhaps you could namespace the nodes (look at the ns attribute in the Attributes section)?

We don't call that remapping any more, but in a sense, the end result is the same.


Edit: after your edit: you'd want to add a ns attribute to your group elements. See the group docs, Attributes. Then remove all the remap elements from your nodes.

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Thanks for your suggestion on the ns attribute. Though this only adds the prefix to the node names. The topics are still under the global namespace / as they have been hardcoded, especially the supposedly internal ones.

Britsk gravatar image Britsk  ( 2020-05-31 13:08:20 -0500 )edit

Then that would be a problem with the way the nodes are implemented. If the topic names have been made fully resolved (ie: global, start with a /) then they cannot be namespaced.

If that's the case, I'm afraid there is no other way than manually remapping everything.

That's actually exactly why you don't want to use global/absolute names.

gvdhoorn gravatar image gvdhoorn  ( 2020-05-31 15:11:18 -0500 )edit

Are these publicly available nodes? If so, could you link us to them?

gvdhoorn gravatar image gvdhoorn  ( 2020-05-31 15:11:45 -0500 )edit

Sure, it's the lio-mapping nodes from the HKUST team here

Britsk gravatar image Britsk  ( 2020-05-31 21:12:52 -0500 )edit

Yes, those nodes advertise(..) absolute/global topic names. Those cannot be namespaced.

I would suggest to log an issue with the maintainers/developers to get this fixed.

In the meantime, you could perhaps remove all the leading / from the topic names in a fork and test whether everything still works (other nodes could assume topics are global, and non-global topics could make them unable to subscribe).

Without fixing those topic names, namespacing will never work.

gvdhoorn gravatar image gvdhoorn  ( 2020-06-01 04:36:28 -0500 )edit

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Asked: 2020-05-31 10:44:46 -0500

Seen: 30 times

Last updated: May 31