How to remap a private parameter

asked 2018-02-21 02:45:27 -0500

Felix Widmaier
382 ●18 ●32 ●40

In a launch file I want to remap parameters of my node to other, already existing parameters. It is working for global parameters but not for private ones.

This is a simple example node "param.py":

#!/usr/bin/env python
"""Just testing parameter mapping."""
import rospy

rospy.init_node("param")
print(rospy.get_param("foo"))
print(rospy.get_param("bar"))
print(rospy.get_param("~baz"))

The node is launched by this launch file "param.launch":

<launch>
    <node name="param" pkg="mypkg" type="param.py" output="screen">
        <remap from="/bar" to="/foo" />
        <remap from="baz" to="foo" />
    </node>
</launch>

In a terminal I run:

rosparam set foo 42
roslaunch mypkg param.launch

The output is:

42
42
KeyError: '~baz'

How can I make it work?

Comments

I'm afraid rosparam would fail without Parameter server running. Maybe add roscore command a line above?

130s ( 2018-09-20 12:47:55 -0500 )edit

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answered 2018-02-21 02:47:04 -0500

Felix Widmaier
382 ●18 ●32 ●40

Private parameter names have to be prefixed with ~ even when the <remap> is defined inside the <node> tag:

<launch>
    <node name="param" pkg="mypkg" type="param.py" output="screen">
        <remap from="/bar" to="/foo" />
        <remap from="~baz" to="foo" />
    </node>
</launch>

Output:

42
42
42

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Comments

Nice dig! Added to remap page.

130s ( 2018-09-20 12:46:53 -0500 )edit

Could it be that this approach does not work for roscpp nodes? The remapping is not applied for NodeHandles created as

ros::NodeHandle private_nh("~"); assert(private_nh.resolveName("baz") == "/param/foo");

with the launch file snippet from this answer.

Or is this not what to expect?

meyerj ( 2020-02-24 14:53:39 -0500 )edit

Furthermore I think what is meant by "assignment for private node parameters" in the original content of the wiki page is not remapping. Both, rospy and roscpp, support assigning parameters via "special" remappings _key:=value, but that is not the same as remapping parameter name ~key to ~value.

meyerj ( 2020-02-24 14:56:10 -0500 )edit

Found the problem with the snippet in my first post: The target of the remapping is not private, so private_nh.resolveName("baz") == "/foo", not "/param/foo".

meyerj ( 2020-02-24 15:05:37 -0500 )edit

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How to remap a private parameter

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