kobuki_gazebo_plugins: request for tf prefix of base_footprint about kobuki_desktop HOT 4 OPEN

This is always tricky as it probably requires sweeping changes across the whole kobuki-turtlebot workspace. I've no clear idea of what it would entail across the whole workspace...so as I said, tricky and would require significant testing.

Indigo would be a better place to experiment making sweeping multi-kobuki tests as we haven't yet officially 'released' there yet and are less likely to disturb people with bugs.

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tf_prefix should work after #34.

So I can configure like this https://github.com/robotics-in-concert/concert_services/blob/indigo/concert_service_gazebo/robots/kobuki/kobuki.launch#L13-L29

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I am trying the roslaunch example that you link to, which is at commit robotics-in-concert/concert_services@ae5a524 at time of writing (so for posterity, your original URL would be https://github.com/robotics-in-concert/concert_services/blob/ae5a524edcb8f99f58f9dad26bc190766731cd64/concert_service_gazebo/robots/kobuki/kobuki.launch#L13-L29).

Upon trying the example, I found that the topic names are correctly placed in a namespace according to the tf_prefix parameter. However, the frame_id of messages on the odom topic of each robot are not reliably correct unless the <param> elements of the launch file are moved to within <node pkg="gazebo_ros" ...>. Unless this is done, the parameter tf_prefix is at the root of the parameter namespace, so each inclusion of the <launch> code (as in the example) rewrites the value of tf_prefix.

My explanation of this behavior is as follows. gazebo_ros_utils, which is now used in the Kobuki Gazebo plugin, assigns to tf_prefix_ using tf::getPrefixParam. This tf function uses the roscpp NodeHandle functions to get the parameter value. The documentation for NodeHandle::searchParam indicates that the parameter tree is crawled up until a match is found. Thus the problem can be solved by making tf_prefix be a parameter within the namespace of the node handle for each plugin instantiation,

<node pkg="gazebo_ros" ...>
   <param name="tf_prefix" value="$(arg name)"/>
</node>

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I just tried the gazebo_concert example in the rocon_tutorials repository and found that the error I describe above does not occur. My previous comment is motivated by an example that does not involve rocon. I am now investigating why the behavior is different.

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