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string argument roslaunch

asked 2014-06-19 14:03:18 -0500

Pototo gravatar image

Hi,

I am trying to pass arguments to my launch file, but I can never get the values that I sent: for instance, I declared my variables this way:

<?xml version="1.0"?>
<launch>

    <arg name="my_KP" />
    <arg name="my_KI" />
    <arg name="my_KD" />
    <arg name="my_EL" />
    <arg name="my_ADT" />

    <node name="en_pub" pkg="driver" type="en_repub.py" />

    <node name="left_motor" pkg="driver" type="left" output="screen">
        <!--
        <param name="KP" type="string" value="$(arg my_KP)" />
        <param name="KI" type="string" value="$(arg my_KI)"/>
        <param name="KD" type="string" value="$(arg my_KD)"/>
        <param name="EL" type="string" value="$(arg my_EL)"/>
        <param name="ADT" type="string" value="$(arg my_ADT)"/>
        -->
    </node>

    <node name="right_motor" pkg="driver" type="right" output="screen">
        <!--
        <param name="KP" type="string" value="$(arg my_KP)" />
        <param name="KI" type="string" value="$(arg my_KI)"/>
        <param name="KD" type="string" value="$(arg my_KD)"/>
        <param name="EL" type="string" value="$(arg my_EL)"/>
        <param name="ADT" type="string" value="$(arg my_ADT)"/>
        -->
    </node>

And on my node I did this:

    ros::NodeHandle p_nh;

    string KP = "1000";
    string KI = "240";
    string KD = "12000";
    string EL = "30000";
    string ADT = "1";

    //This allows for setting params instead of recompile to change
    p_nh.param<string>("KP", KP, "1000");
    p_nh.param<string>("KI", KI, "240");
    p_nh.param<string>("KD", KD, "12000");
    p_nh.param<string>("EL", EL, "30000");
    p_nh.param<string>("ADT", ADT, "1");

But my program does not seem to catch them. I only get the assigned default values.

What am I doing wrong?

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1 Answer

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answered 2014-06-19 17:28:30 -0500

updated 2014-06-19 17:35:07 -0500

I believe that the problem is that in your launch file, the params are all private params (as they are in the node tag). Therefore you can either declare a private nodehandle i.e. your first line of C++ would read

ros::NodeHandle p_nh("~");

or you could use the "bare" versions from the API i.e. your parameter calls would read something like

ros::param::param<string>("~KI", KI, "240");

Here's a complete C++ file that does it both ways:

#include <ros/ros.h>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
    ros::init(argc, argv, "test");
    ros::NodeHandle nh("~");

    string KP = "1000";
    string KI = "240";

    nh.param<string>("KP", KP, "1000");
    ros::param::param<string>("~KI", KI, "240");

    ROS_INFO("KP = %s", KP.c_str());
    ROS_INFO("KI = %s", KI.c_str());

    return 0;
}
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Comments

In your attached launch file, your params are commented out. I'm assuming you didn't mean to post it this way.

jarvisschultz gravatar image jarvisschultz  ( 2014-06-19 17:36:35 -0500 )edit

Great! This works, thanks!

Pototo gravatar image Pototo  ( 2014-06-20 15:54:19 -0500 )edit

Why isn't this in the tutorials? I went crazy looking for this 0.o

Robocop87 gravatar image Robocop87  ( 2015-02-16 03:22:39 -0500 )edit
1
jarvisschultz gravatar image jarvisschultz  ( 2015-02-16 14:36:07 -0500 )edit
1

Here's a description of private params in general: http://wiki.ros.org/Parameter%20Serve... And here's the roslaunch XML documentation on <param> describing its behavior inside of the <node> tag http://wiki.ros.org/roslaunch/XML/param

jarvisschultz gravatar image jarvisschultz  ( 2015-02-16 14:37:48 -0500 )edit
1

Hopefully those links clear up any remaining confusion!

jarvisschultz gravatar image jarvisschultz  ( 2015-02-16 14:49:54 -0500 )edit

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Asked: 2014-06-19 14:03:18 -0500

Seen: 3,769 times

Last updated: Jun 19 '14