roscpp relative parameter

parameter

asked 2011-09-01 23:13:32 -0500

andreas
168 ●7 ●8 ●13

Hi,

I somehow can't manage to get or search relative parameter names. What I do is, I launch a launch file which sets parameters.

<launch>
  <node pkg="test" type="test_node" name="test_node"> 
    <param name="testparameter" value="a" />
    <param name="show_windows" value="true" />
    <rosparam file="$(find test)/config/params.yaml" command="load"/>
  </node>
</launch>

This all works, I can get and set parameters using rosparam via the shell. They are published over e.g. /test_node/orientations, /test_node/kernels/kernel_1/wavelength, /test_node/kernels/kernel_2/wavelength and so on. Now within the test node I want to read those parameter. But when I try

nh_.getParam("orientations", orientations_list);

The parameter won't be found, I have to explicitly name the whole global name "/test_node/orientations". I have the same issue with

nh_.searchParam("orientations", orientations_param_name);

Am I doing something wrong? Is there a way to get the current namespace the node is in as a workaround?

(I'm using Ubuntu 10.04.1, 64 bit with the standard ros diamondback package from the package manager)

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answered 2011-09-02 00:10:39 -0500

dornhege

31395 ●134 ●284 ●498

To read parameters from the node's namespace create a private NodeHandle as:

NodeHandle nhPriv("~");
nhPriv.getParam...

Use this nodehandle to access the parameters and it will work. This is actually not a workaround but the preferred way to do it.

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answered 2011-09-02 03:25:36 -0500

andreas
168 ●7 ●8 ●13

Thanks, now it worked. I'm still a bit confused because in the tutorial

http://www.ros.org/wiki/roscpp/Overview/Parameter%20Server

it says

ros::NodeHandle nh;
std::string global_name, relative_name, default_param;
if (nh.getParam("/global_name", global_name))
{
  ...
}

if (nh.getParam("relative_name", relative_name))
{
...
}

But nh.getParam("relative_name", relative_name) shouldn't work when the NodeHandle isn't private, right?

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1

Yes I am confused too. When and Why would i use relative_name then ? And why does it even exist ? This tutorial says we can use relative name if we use the corresponding node handle

ROSfc ( 2016-09-01 10:01:30 -0500 )edit

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answered 2011-09-02 04:01:42 -0500

joq
25443 ●181 ●256 ●408

It seems there is some confusion here about the difference between "relative" names and "private" names. You defined private parameters, which must be resolved using the "~" node handle, as Dornhege described. See this wiki page for more details. Relative names can be resolved via the node's address space, but not private ones.

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