Tutorial: Using roslaunch to start Gazebo, world files and URDF models

Tutorial: Using roslaunch to start Gazebo, world files and URDF models

参考：http://gazebosim.org/tutorials?tut=ros_roslaunch&cat=connect_ros

1. 使用roslaunch 打开仿真模型

  参数：

paused              Start Gazebo in a paused state (default false)

usesimtime      Tells ROS nodes asking for time to get the Gazebo-published simulation time, published over the ROS topic /clock (default true)

gui                     Launch the user interface window of Gazebo (default true)

headless           Disable any function calls to simulator rendering (Ogre) components. Does not work with gui:=true (default false)

debug              Start gzserver (Gazebo Server) in debug mode using gdb (default false)

1.1     empty_world.launch

roslaunch gazebo_ros empty_world.launch

  <arg name="paused" default="false"/>
  <arg name="use_sim_time" default="true"/>
  <arg name="extra_gazebo_args" default=""/>
  <arg name="gui" default="true"/>
  <arg name="headless" default="false"/>
  <arg name="debug" default="false"/>
  <arg name="physics" default="ode"/>
  <arg name="verbose" default="false"/>
  <arg name="world_name" default="worlds/empty.world"/>  

roslaunch gazebo_ros empty_world.launch paused:=true use_sim_time:=false gui:=true throttled:=false headless:=false debug:=true

1.2  mud_world.launch  


继承自emptyworld.launch文件，并将涉及需要的参数进行改变。  ===》word 文件


rosed gazebo_ros mud_world.launch

<launch>

  <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="worlds/mud.world"/> <!-- Note: the world_name is with respect to GAZEBO_RESOURCE_PATH environmental variable -->
    <arg name="paused" value="false"/>
    <arg name="use_sim_time" value="true"/>
    <arg name="gui" value="true"/>
    <arg name="headless" value="false"/>
    <arg name="debug" value="false"/>
  </include>

</launch>

1.3  World Files

先找三个gazebo的模型，先从本地gazebo模型库中找，路径在.gazebo/models ，找不到再从网络在线库（需要链接到goole,这已经被墙了）

  <sdf version="1.4">
    <world name="default">
      <include>
        <uri>model://sun</uri>
      </include>
      <include>
        <uri>model://ground_plane</uri>
      </include>
      <include>
        <uri>model://double_pendulum_with_base</uri>
        <name>pendulum_thick_mud</name>
        <pose>-2.0 0 0 0 0 0</pose>
      </include>
      ...
    </world>
  </sdf>

2. Creating your own Gazebo ROS Package

文件夹

/MYROBOT_description      机器人模型与描述文件

/MYROBOT_gazebo                 world文件与launch文件   

../catkin_ws/src      文件夹结构 
    /MYROBOT_description
        package.xml
        CMakeLists.txt
        /urdf
            MYROBOT.urdf
        /meshes
            mesh1.dae
            mesh2.dae
            ...
        /materials
        /cad
    /MYROBOT_gazebo
        /launch
            MYROBOT.launch
        /worlds
            MYROBOT.world
        /models
            world_object1.dae
            world_object2.stl
            world_object3.urdf
        /materials
        /plugins

2.1 建world 文件

  建launch文件夹    YOUROBOT.launch

<launch>
  <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find MYROBOT_gazebo)/worlds/MYROBOT.world"/>
    <!-- more default parameters can be changed here -->
  </include>
</launch>

  建 world文件夹      MYROBOT.world

<?xml version="1.0" ?>
<sdf version="1.4">
  <world name="default">
    <include>
      <uri>model://ground_plane</uri>
    </include>
    <include>
      <uri>model://sun</uri>
    </include>
    <include>
      <uri>model://gas_station</uri>
      <name>gas_station</name>
      <pose>-2.0 7.0 0 0 0 0</pose>
    </include>
  </world>
</sdf>

用launch gazebo加载world文件

roslaunch MYROBOT_gazebo MYROBOT.launch

 编辑world文件，可以依据gazebo 进行添加model，File->Save保存即可.

3. Using roslaunch to Spawn URDF Robots

3.1 ROS Service Call Spawn Method   推荐 

将机器人的描述文件可以分开，利用 spawn_model脚本在相应包里调用就可以。  简化了包的存储结构。     

keep your robot's location relative to a ROS package path, but also requires you to make a ROS service call using a small (python) script.

使用脚本语句 spawn_model调用节点gazebo_ros的服务回调加载URDF文件到gazebo中，相应参数。

URDF Example with Baxter

下载Baxter模型包，

git clone https://github.com/RethinkRobotics/baxter_common.git

运行 gazebo_ros 与 脚本 spawn_model 加载机器人。

rosrun gazebo_ros spawn_model -file `rospack find MYROBOT_description`/urdf/MYROBOT.urdf -urdf -x 0 -y 0 -z 1 -model MYROBOT

This method uses a small python script called spawn_model to makea service call request to the gazebo_ros ROS node(named simply "gazebo" in the rostopic namespace) to add a custom URDF into Gazebo.The spawn_model script is located within the gazebo_ros package.You can use this script in the following way:

rosrun gazebo_ros spawn_model -file `rospack find MYROBOT_description`/urdf/MYROBOT.urdf -urdf -x 0 -y 0 -z 1 -model MYROBOT

To see all of the available arguments for spawn_model including namespaces, trimesh properties, joint positions and RPY orientation run:

rosrun gazebo_ros spawn_model -h

----------也可以放到launch文件里，与world一起加载。

XACRO Example with PR2URDF is not in XML format but rather in XACRO format,  XACRO格式的urdf文件。

<!-- Spawn a robot into Gazebo -->
<node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-file $(find baxter_description)/urdf/baxter.urdf -urdf -z 1 -model baxter" />

sudo apt-get install ros-indigo-pr2-common

在launch里面加载机器人描述

<!-- Convert an xacro and put on parameter server -->
<param name="robot_description" command="$(find xacro)/xacro.py $(find pr2_description)/robots/pr2.urdf.xacro" />

<!-- Spawn a robot into Gazebo -->
<node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-param robot_description -urdf -model pr2" />

3.2 Model Database Method

    自己 建gazebo 模型

../catkin_ws/src
    /MYROBOT_description
        package.xml
        CMakeLists.txt
        model.config
        /urdf
            MYROBOT.urdf
        /meshes
            mesh1.dae
            mesh2.dae
            ...
        /materials
        /plugins
        /cad

• /home/user/catkin_workspace/src - this is treated as the location of a Gazebo Model Database
• /MYROBOT_description - this directory is treated as a single Gazebo model folder                                                   模型文件夹
  
• model.config - this is a required configuration file for Gazebo to find this model in its database                              配置描述性信息
  
• MYROBOT.urdf - this is your robot description file, also used by Rviz, MoveIt!, etc                                                    
  
• /meshes - put your .stl or .dae files in here, just as you would with regular URDFs

Environment Variable         -tells Gazebo where to look for model databases

  export GAZEBO_MODEL_PATH=/home/user/catkin_ws/src/

Next Steps

Now that you know how to create roslaunch files that open Gazebo, world files and URDF models, you are now ready to create your own Gazebo-ready URDF model in the tutorialUsing A URDF In Gazebo