URDF 파일 구조 설명

http://gazebosim.org/tutorials?tut=ros_roslaunch

"Model Database" Robot Spawn Method

The second method of spawning robots into Gazebo allows you to include your robot within the .world file, which seems cleaner and more convenient but also requires you to add your robot to the Gazebo model database by setting an environment variable. This environment variable is required because of the separation of ROS dependencies from Gazebo; URDF package paths cannot be used directly inside .world files because Gazebo does not have a notion of ROS packages.

To accomplish this method, you must make a new model database that contains just your single robot. This isn't the cleanest way to load your URDF into Gazebo but accomplishes the goal of not having to keep two copies of your robot URDF on your computer. If the following instructions are confusing, refer back to the Gazebo Model Database documentation to understand why these steps are required.

We will assume your ROS workspace file hierarchy is setup as described in the above sections. The only difference is that now a model.config file is added to your MYROBOT_description package like so:

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

This hierarchy is specially adapted for use as a Gazebo model database by means of the following folders/files:

• /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
• model.config - this is a required configuration file for Gazebo to find this model in its database
• 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

model.config

Each model must have a model.config file in the model's root directory that contains meta information about the model. Basically copy this into a model.config file, replacing MYROBOT.urdf with your file name:

  <?xml version="1.0"?>
  <model>
    <name>MYROBOT</name>
    <version>1.0</version>
    <sdf>urdf/MYROBOT.urdf</sdf>
    <author>
      <name>My name</name>
      <email>name@email.address</email>
    </author>
    <description>
      A description of the model
    </description>
  </model>

Unlike for SDFs, no version is required for the tag when it is used for URDFs. See the Gazebo Model Database documentation for more info.

Environment Variable

Finally, you need to add an environment variable to your .bashrc file that tells Gazebo where to look for model databases. Using the editor of your choice edit "~/.bashrc". Check if you already have a GAZEBO_MODEL_PATH defined. If you already have one, append to it using a semi-colon, otherwise add the new export. Assuming your Catkin workspace is in ~/catkin_ws/ Your path should look something like:

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

Viewing In Gazebo - Manually

Now test to see if your new Gazebo Model Database is properly configured by launching Gazebo:

  gazebo

And clicking the "Insert" tab on the left. You will probably see several different drop down lists that represent different model databases available on your system, including the online database. Find the database corresponding to your robot, open the sub menu, click on the name of your robot and then choose a location within Gazebo to place the robot, using your mouse.

Viewing In Gazebo - roslaunch with the Model Database

The advantage of the model database method is that now you can include your robot directly within your world files, without using a ROS package path. We'll use the same setup from the section "Creating a world file" but modify the world file:

• Within the same MYROBOT_description/launch folder, edit the MYROBOT.world file with the following contents:

<?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>
    <include>
      <uri>model://MYROBOT_description</uri>
    </include>
  </world>
</sdf>

• You should now be able to launch your custom world with both the gas station and robot into Gazebo using the following command:

  roslaunch MYROBOT_gazebo MYROBOT.launch
  

The disadvantage of this method is that your packaged MYROBOT_description and MYROBOT_gazebo are not as easily portable between computers - you first have to set the GAZEBO_MODEL_PATH on any new system before being able to use these ROS packages.

Exporting model paths from a package.xml

The useful info would be the format for exporting model paths from a package.xml:

<run_depend>gazebo_ros</run_depend>
<export>
  <gazebo_ros gazebo_model_path="${prefix}/models"/>
  <gazebo_ros gazebo_media_path="${prefix}/models"/>
</export>

The '${prefix}` is something that new users might not immediately know about either, and necessary here.

Also would be useful to have some info on how to debug these paths from the ROS side, e.g. that you can use rospack plugins --attrib="gazebo_media_path" gazebo_ros To check the media path that will be picked up by gazebo.