Can not retrieve parameters

Question

I am running ur5_moveit_config demo.launch from ros-industrial's universal robot package and I'd like to control it from my node. For that purpose I need to retrieve several parameters from parameter server. The first one is planning_plugin.

Calling rosparam list | grep planning_plugin gives /move_group/planning_plugin. Which means that parameter exists.

Here is my node initialization code:

#include <ros/ros.h>
#include <pluginlib/class_loader.h>

/* Moveit includes */
#include <moveit/robot_model/robot_model.h>
#include <moveit/robot_model_loader/robot_model_loader.h>
#include <moveit/planning_scene/planning_scene.h>
#include <moveit/planning_interface/planning_interface.h>
#include <moveit_msgs/DisplayTrajectory.h>
#include <moveit_msgs/PlanningScene.h>
#include <moveit/kinematic_constraints/utils.h>

#include <iostream>
#include <boost/scoped_ptr.hpp>

int main(int argc, char **argv) {
    ros::init(argc, argv, "arm_control_node");
    ros::AsyncSpinner spinner(1);
    spinner.start();
    ros::NodeHandle node_handle("/move_group/arm_control");
    
    std::string planner_plugin_name; //= "ompl_interface/OMPLPlanner";
    
    if (!node_handle.getParam("planning_plugin", planner_plugin_name)) {
        ROS_FATAL_STREAM("Could not find planner plugin name");
    }

    return 0;
}

Launching executable with rosrun arm_control arm_control_node prints [FATAL] [1508419005.957461571]: Could not find planner plugin name. However rosparam get /move_group/planning_plugin outputs ompl_interface/OMPLPlanner.

I have tried to hardcode plugin name as a result I have got an error about retrieving other parameters. It seems like the node can not get access to them but why is a mystery for me.

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Originally posted by Long Smith on ROS Answers with karma: 75 on 2017-10-19

Post score: 0

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Original comments

Comment by gvdhoorn on 2017-10-19:\

I'd like to control it from my node

looking at your #includes: are you planning to load planning plugins directly? That is possible, but just wanted to make sure you are aware there is a ROS API (ie: services and actions) available that is probably much easier to use.

Comment by Long Smith on 2017-10-19:
@gvdhoorn Thanks again! Gonna take a look. It is just a part of the motion_planning_api_tutorial from moveit page. Wonder why do they use direct plugin loading if there are easier methods to do so.

Answer 1

ros::NodeHandle node_handle("/move_group/arm_control");

...
node_handle.getParam("planning_plugin", ...);

and:

Launching executable with rosrun arm_control arm_control_node prints [FATAL] [1508419005.957461571]: Could not find planner plugin name. However rosparam get /move_group/planning_plugin outputs ompl_interface/OMPLPlanner.

Parameter lookups are relative to the ros::NodeHandle that you do them with.

In this case you ask for planning_plugin with a NodeHandle that you created in the /move_group/arm_control namespace. So in the end, node_handle will try to retrieve /move_group/arm_control/planning_plugin for you.

That parameter doesn't exist, hence the error.

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Do you have a specific reason for creating your main ros::NodeHandle in that namespace?

It is perfectly ok to create NodeHandles in namespaces like that, but especially the "first one" is typically created without any namespace declaration at all.

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Originally posted by gvdhoorn with karma: 86574 on 2017-10-19

This answer was ACCEPTED on the original site

Post score: 2

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Original comments

Comment by Long Smith on 2017-10-19:
Yeah, I've read about it. Actually that was just one of the many attempts to make it work but the first one used global resolution node_handle.getParam("/move_group/planning_plugin", ...) and it failed for some reason(wonder if it was a type since I checked spelling).

Comment by Long Smith on 2017-10-19:
Whatsoever it was, now, thanks to your answer, it works.