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Gazebo topic publication issue within namespaced group tag

asked 2016-08-03 08:08:17 -0600

JaredMoore gravatar image

updated 2016-08-04 07:40:14 -0600

ROS Kinetic
Gazebo 7.0
RedHat Linux

I'm running into an issue with a roslaunch file that attempts to start a Gazebo node within a group tag that has the namespace parameter set. The Gazebo node appears to start, but other nodes that wait on gazebo services hang. Specifically, when using rospy, the following calls do not complete.

rospy.wait_for_service('/gazebo/get_world_properties')
rospy.wait_for_service('/gazebo/reset_world')
rospy.wait_for_service('/gazebo/reset_simulation')
rospy.wait_for_service('/gazebo/pause_physics')
rospy.wait_for_service('/gazebo/unpause_physics')

The launch file is as follows:

<launch>

<!-- ********************* Begin Gazebo Defaults ******************************** -->

<!-- these are the arguments you can pass this launch file, for example paused:=true -->
  <arg name="paused" default="true"/>
  <arg name="use_sim_time" default="true"/>
  <arg name="gui" default="false"/>
  <arg name="headless" default="true"/>
  <arg name="debug" default="false"/>

  <!-- these are the arguments you can pass this launch file, for example paused:=true -->
  <arg name="extra_gazebo_args" default=""/>
  <arg name="physics" default="ode"/>
  <arg name="verbose" default="true"/>
  <arg name="world_name" value="$(find basicbot_gazebo)/worlds/basicbot.world"/>
  <arg name="respawn_gazebo" default="false"/>
  <arg name="use_clock_frequency" default="false"/>
  <arg name="pub_clock_frequency" default="100"/>

  <!-- set use_sim_time flag -->
  <group if="$(arg use_sim_time)">
    <param name="/use_sim_time" value="true" />
  </group>

  <!-- set command arguments -->
  <arg unless="$(arg paused)" name="command_arg1" value=""/>
  <arg     if="$(arg paused)" name="command_arg1" value="-u"/>
  <arg unless="$(arg headless)" name="command_arg2" value=""/>
  <arg     if="$(arg headless)" name="command_arg2" value="-r"/>
  <arg unless="$(arg verbose)" name="command_arg3" value=""/>
  <arg     if="$(arg verbose)" name="command_arg3" value="--verbose"/>
  <arg unless="$(arg debug)" name="script_type" value="gzserver"/>
  <arg     if="$(arg debug)" name="script_type" value="debug"/>

  <group if="$(arg use_clock_frequency)">
    <param name="gazebo/pub_clock_frequency" value="$(arg pub_clock_frequency)" />
  </group>

<!-- ********************* End Gazebo Defaults ******************************** -->    

<!-- <group ns="basicbot_ga_1"> -->
<group ns="ga1">
  <!-- start gazebo server-->
  <env name="GAZEBO_MASTER_URI" value="http://localhost:11345"/>
  <node name="gazebo" pkg="gazebo_ros" type="$(arg script_type)" respawn="$(arg respawn_gazebo)" 
    output="screen" args="$(arg command_arg1) $(arg command_arg2) $(arg command_arg3) -e $(arg physics) 
    $(arg extra_gazebo_args) $(arg world_name)">
  </node>

  <!-- Load the transporter node -->
  <node name="basicbot_transporter" pkg="basicbot_ga" type="basicbot_transporter.py" output="screen"></node>

    <!-- Load the turn_drive_scan node -->
    <node name="turn_drive_scan" pkg="basicbot_ga" type="turn_drive_scan_node.py" output="screen"></node>

    <!-- Load the step world node -->
  <node name="step_world" pkg="world_step" type="step_world_server"/>

  <!-- Load the URDF into the ROS Parameter Server -->
  <param name="robot_description"
    command="$(find xacro)/xacro '$(find basicbot_description)/urdf/basicbot.xacro'" />

  <!-- Run a python script to the send a service call to gazebo_ros to spawn a URDF robot -->
  <node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model" respawn="false" output="screen"
    args="-urdf -model basicbot -param robot_description"/>
</group>

</launch>

I've tried the following while troubleshooting the problem.

  1. Remove group tag completely. Behavior: Simulation runs fine, nodes initialize and execute after the initial spool up.
  2. Add group tag without ns attribute. Behavior: Simulation again runs fine.
  3. Add ns attribute. Behavior: Gazebo node appears to launch, but the previously mentioned services do not appear to be available to other nodes inside the group tag. rostopic list and gz topic -l do not show the topics being published either.

As far as I can tell, adding the ... (more)

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2 Answers

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answered 2016-08-04 08:41:04 -0600

JaredMoore gravatar image

I was able to solve this issue this morning. I did not end up needing the robotName or robotNamespace tags as suggested. Instead, my issue was due to the fact that gazebo was launching as /ga1/gazebo, forcing the services it offered to be changed from /gazebo/<service> to /ga1/gazebo/<service>. The launch file was still however looking for /gazebo/<service>, especially in the case of the urdf_spawn node. Accordingly, I changed

<node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model" respawn="false" output="screen"
    args="-urdf -model basicbot -param robot_description"/>

to

<node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model" respawn="false" output="screen"
    args="-urdf -model basicbot -param robot_description -gazebo_namespace /ga1/gazebo"/>

by adding the -gazebo_namespace /ga1/gazebo attribute at the end of the call. Be sure also to make changes to any scripts that use rospy and wait_for_service or ServiceProxy as you will need to prepend the namespace to those as well by calling rospy.get_namespace().

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Not enough points to accept this as an answer, but it is the fix.

JaredMoore gravatar imageJaredMoore ( 2016-08-04 08:41:30 -0600 )edit
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answered 2016-08-04 03:17:35 -0600

F.Brosseau gravatar image

If you are using plugins in your robot's description file, you should add a parameter to your robot_description :

<param name="robot_description"
    command="$(find xacro)/xacro '$(find basicbot_description)/urdf/basicbot.xacro' robotName:=gal" />

And in your xacro files inside the plugins tags you will add :

<robotNamespace>$(arg robotName)</robotNamespace>
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Thank you for the suggestion, I have made the advised changes but am still running into the same issue. I suspect that I will need the proposed changes as well so I have left them in. See Edit 1 for an explanation. It seems some parts of Gazebo are not starting or are lost in a ns conflict.

JaredMoore gravatar imageJaredMoore ( 2016-08-04 07:41:38 -0600 )edit

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Asked: 2016-08-03 08:08:17 -0600

Seen: 364 times

Last updated: Aug 04 '16