Thanks to gvdhoorn's comments, I've managed to set up some basic test which can launch a variable number of namespaces (and thus should also be capable of launching nodes in those namespaces) using recursion through including launch files.
The follow code is the launch file which called 'top_sfm_mpdm_launch.launch' and is the launch file which is called in the terminal with roslaunch.
<launch>
<arg name="robotlist_string" default="_rdg01_rdg02_rdg03" doc="A string of robot namespace IDs prefixed with _'s. Default: '_rdg01_rdg02_rdg03'." />
<rosparam param="robotlist_string_num" subst_value="True">$(eval arg('robotlist_string').count("_"))</rosparam>
<include file="$(find sfm_mpdm)/launch/recursion_test.launch">
<!-- all vars that recursion_test.launch requires must be set -->
<arg name="robot_number" value="$(eval arg('robotlist_string').count('_'))" />
<arg name="recursion_depth" value="1" />
<arg name="robotlist_string" value="$(arg robotlist_string)" />
</include>
</launch>
The included file 'recursion_test.launch' has the following code:
<launch>
<arg name="robot_number" />
<arg name="recursion_depth" />
<arg name="robotlist_string" />
<rosparam param="robot_number" subst_value="True">$(arg robot_number)</rosparam>
<rosparam param="recursion_depth" subst_value="True">$(arg recursion_depth)</rosparam>
<arg name="offset" value="$(eval (arg('recursion_depth')-1) * 6)" />
<arg name="namespace" value="$(eval arg('robotlist_string')[ arg('offset')+1 : arg('offset')+6 ])" />
<group ns="$(arg namespace)">
<rosparam param="robot_namespace" subst_value="True">$(arg namespace)</rosparam>
</group>
<include file="$(find sfm_mpdm)/launch/recursion_test.launch" unless="$(eval arg('recursion_depth') == arg('robot_number'))">
<!-- all vars that recursion_test.launch requires must be set -->
<arg name="robot_number" value="$(arg robot_number)" />
<arg name="recursion_depth" value="$(eval arg('recursion_depth')+1)" />
<arg name="robotlist_string" value="$(arg robotlist_string)" />
</include>
</launch>
The command used to launch the setup is: roslaunch sfm_mpdm top_sfm_mpdm.launch robotlist_string:=_rdg01_rgd02_rdg03_rsb06
Which produces the following parameters on the parameter server (parameter server was used for debugging and testing, you can of course launch nodes with this):
PARAMETERS
* /rdg01/robot_namespace: rdg01
* /rdg03/robot_namespace: rdg03
* /recursion_depth: 4
* /rgd02/robot_namespace: rgd02
* /robot_number: 4
* /robotlist_string_num: 4
* /rosdistro: melodic
* /rosversion: 1.14.5
* /rsb06/robot_namespace: rsb06
(1) Now as you might have noticed. I'm using a roslaunch argument (robotlist_string) with a string _id_id_id_id e.g. _rdg01_rsb01_rdg_05_rsb_02_rsb_12 which isn't ideal. I'd rather be able to use a list of id strings, but I couldn't get this to work with eval.
(2) Similarly, I couldn't get < or <= to work with eval. So the recursion depth checking is a bit too finicky for my liking and could quite easily end up in an infinite loop..
Any help on the above two mentioned issues (1 & 2) would be great! :)
roslaunchdoes not support this directly. There is no loop construct. Perhaps recursion could be used, but I haven't tried whether it'll work.All parameters are stored on the parameter server before anything else is started (ie: nodes), so there are essentially two phases: store configuration on parameter server, then start nodes. There is no "read from parameter server" phase in between.
Hmm ok, so the only variable input which can be given to a launch file is as an argument in the roslaunch command.
Say we get a param inside the launch file which contains the list [rdg01,rdg02,rbt05], then the next issue is, how do we iterate over this list, retrieve the namespace of each robot and set that as an arg for later usage in the namespace tag, especially since the number of items in the list varies. Any ideas?
You also mentioned recursion, which I assume would be including the launchfile itself with an include tag. This tag should imo be wrapped in a conditional which checks if the desired depth is reached to prevent infinite self launching. Which brings up the question of how to deal with counters in conditionals inside XML.. I'll look into this, but any knowledge shared is appreciated.
Yes.
Of course.
Not "XML", but in
roslaunchXML. Androslaunchsupports passing arguments toincluded.launchfiles, which in turn can use Python expressions inargs. So it might be possible to pass a counterargto anincluded.launch, have that.launchsubtract 1, pass theargon to another and instantiate whatever it wants with the value of the counter it was passed in its "layer" of recursion.But again: I've not tested this, so there could be something which makes this "not work".
And we're of course really zooming in on implementation ...(more)
I've managed to set up the basic recursion as a test. I must say it feels a bit finicky because I couldn't use < <= operators inside the eval. I had to resort to using:
Where the recursion_depth starts at 1 and is increment with each include. The robot_number is derived from the roslaunch argument (string):
Using the following eval:
But it seems working with a test; As a test it sets up a range of variables, each in their own namespaces (rdg01, rdg02, etc..). Which are derived from the string robotlist_string.
Shall I post the solution code as an answer (limited amount of characters here), allowing further improvements there using comments?
After some time: #q229489 is essentially a duplicate I believe.