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Yaml file loaded in the parameter server but disappears after.

asked 2019-01-28 06:08:47 -0500

oiseau gravatar image

Hello everyone,

I have an issue with my parameters, when I launched my launch file where I load the yaml file, I can see that parameters from the yaml file are being loaded to the parameter server, but when I look after with rostopic list, there is no trace of my parameters anymore.

I load the yaml file with this :

<group ns="structure">
<rosparam command="load" file="$(find approche)/config/structure.yaml" />
</group>

In the terminal, I got :

PARAMETERS
 * /rosdistro: kinetic
 * /rosversion: 1.12.14
 * /structure/angle: 120
 * /structure/bras: 3
 * /structure/longueur: 550

But, there is nothing of that in Rostopic list or with rqt_graph...

I am using Kinetic with Ubuntu 16.

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answered 2019-01-28 07:00:12 -0500

Delb gravatar image

Parmaters are not like topics, as you said they are loaded into the parameter server. In the introduction of the wiki :

A parameter server is a shared, multi-variate dictionary that is accessible via network APIs. Nodes use this server to store and retrieve parameters at runtime. As it is not designed for high-performance, it is best used for static, non-binary data such as configuration parameters. It is meant to be globally viewable so that tools can easily inspect the configuration state of the system and modify if necessary.

The Parameter Server is implemented using XMLRPC and runs inside of the ROS Master, which means that its API is accessible via normal XMLRPC libraries.

So it's not a node that stores the parameters and publish them to the other nodes. The parameters can be read/set via your code or with the tool rosparam .

So instead of rostopic list you can see the parameters with rosparam list. For example if you want to check the value of all your parameters at once you can use rosparam get /structure/ that will return {angle: 120, bras: 3, longueur: 550}

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Ok, my bad, I am not sure if I open a new question or change this one. I was thinking that my parameters weren't visible to everyone because I got some odd value from the parameter sever in my C++ code. But I didn't remember that rosparam and rostopic are not the same.

oiseau gravatar image oiseau  ( 2019-01-28 07:17:40 -0500 )edit

If you have a different question with the parameters you can open a new one yes, if you still have an issue related to the original question you can edit it to add informations and if the question has been answered you can mark the answer as correct (with the check mark icon next to the answer)

Delb gravatar image Delb  ( 2019-01-28 07:28:43 -0500 )edit

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Asked: 2019-01-28 06:08:47 -0500

Seen: 200 times

Last updated: Jan 28 '19