Creating custom worlds will allow you to expand on the VRX simulation basics to apply the tools to your own work and to future RobotX competitions. In this tutorial we will build an example world with an assortment of tasks that could be used in RobotX 2020. The goal is for teams to learn how to use VRX to accelerate their development and preparation for RobotX 2020.

• Adding Course Elements
• Randomized Obstacle Course
• Create Custom Docks

For this tutorial you will create you own ROS package called rxi to contain the custom world definition. This ROS package should be in the same catkin workspace as the VRX packages. The following instructions assume that your catkin workspace is named '~/vrx_ws'.

Make a new directory for the ROS package, initialize the package by creating blank CMakeLists.txt and package.xml files and build.

cd ~/vrx_ws/src/
mkdir rxi
catkin_create_pkg rxi --rosdistro melodic
cd ~/vrx_ws
catkin_make

Make ROS aware of the new package by

source ~/vrx_ws/devel/setup.bash

Optional: This is a good time to setup version control for your rxi package. If you are familiar with version control (e.g., git

Make new directories in your rxi package and copy existing launch and world files from the vrx_gazebo package to provide a working example.

cd ~/vrx_ws/src/rxi
mkdir launch
mkdir worlds
cd launch
roscp vrx_gazebo vrx.launch ./rxi.launch
cd ../worlds/
roscp vrx_gazebo sandisland.world.xacro rxi.world.xacro

Next we will edit our new files so that we can verify they are a working starting point for creating a custom environment.

The rxi.world.xacro file uses the xacro (XML Macros) utility to generate a Gazebo world file. The file currently creates the basic Sand Island environment, an ocean wave model and an ocean wind model. In order to setup the package to process the xacro file we'll want to do the following within the rxi package:

• Edit the package.xml file and add the following line:

  <depend>xacro</depend>
  

• Edit the CMakeLists.txt file and add the following lines at the bottom of the file:

find_package(catkin REQUIRED COMPONENTS
  xacro)

catkin_package(
  CATKIN_DEPENDS xacro)

# Generate world files from xacro and install
xacro_add_files(
  worlds/rxi.world.xacro
  INORDER INSTALL DESTINATION worlds)

# Install all the world files
install(DIRECTORY worlds/
  DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}/worlds)

• Re-make: (Note that each time you make changes to the rxi.world.xacro file you will need to run catkin_make for those changes to take effect.)

catkin_make

When you build the package the rxi.world.xacro file is processed, generating the rxi.world file that is installed in the system. (To see where try find ~/vrx_ws -name "rxi.world").

Next we will edit the rxi.launch file so that it uses the generated rxi.world file.

• Edit rxi.launch and change the default value of the world argument to point to the new rxi.world file in the rxi ROS package.

• To do this:

  • You'll need to change the argument after find from vrx_gazebo to rxi.
  • You'll also need to change the file name from example_course.world to rxi.world.

• Test your new launch file with...

source devel/setup.bash 
roslaunch rxi rxi.launch

This should generate a Gazebo window that looks something like this...

The vrx_gazebo package includes a number of RobotX specific models (see vrx_gazebo/models). These models are accessible through the Gazebo client GUI, but we will add them to the World file in order to create reusable worlds for development and practice.

Start by adding an instance of green navigational mark by adding the following text to the rxi.world.xacro file. Place this XML block directly before the closing </world> tag.

  <include>
    <name>green_buoy_0</name>
    <uri>model://surmark950400</uri>
    <pose>0 0 0 0 0 0</pose>
  </include>

Test by rebuilding and running this simulation:

catkin_make
roslaunch rxi rxi.launch

You should see that the buoy is located at the origin of the gazebo coordinate frame as shown in the image below.

The tag specifies the position and orientation of the model, so in the example above the buoy is located at the origin of the gazebo coordinate frame. We can change the position by editing the values with the pose tag.

For visually composing a scene it is often convenient to drag the objects using the translate tool. You can select the buoy model, then select the translate tool and move the buoy where you would like. Here is a short video illustrating the process.

You can also edit the pose property of the model directly in the Gazebo client. Select the model in the list of models and expand the properties pane below. Then you can edit the x and y values to move the model.

Position the buoy in front of the WAM-V and then record the x and y position values. Edit the rxi.world.xacro file so that the pose includes your new x and y values so that when you restart the simulation the buoy will appear in the same location. In the block below, replace X and Y with the values from the client GUI.

  <include>
    <uri>model://surmark950400</uri>
    <pose>X Y 0 0 0 0</pose>
  </include>

To exercise these new skills, build a simple navigation challenge course that we might use to practice for RobotX 2020.

• Include two red buoys
• Include two green buoys
• Position the four buoys so that there is a red-green pair near the WAM-V and a pair farther from the WAM-V

When you are done, you should be able to roslaunch rxi rxi.launch and start a simulation world that looks similar to the image below.

Above we learned how to build a world by assembling model instances. This is very useful for creating practice worlds to exercise and test your solutions. As we learn about the RobotX 2020 tasks, many teams will want to create simulated representations of those tasks to start working on solutions.

We may also want a way to quickly generate randomized worlds so that we can practice with lots of different scenarios for a particular task. For RobotX 2018 the UF team created a Python program to generate a randomized obstacle field model. Notes on this contribution to VRX are in PR#54.

The program makes use of a number of command line arguments to output an SDF model file to standard out. Review the usage notes for the program with

rosrun vrx_gazebo generate_avoid_obstacles_buoys -h

• Create a model directory within the rxi package

cd ~/vrx_ws/src/rxi/
mkdir -p models/rxi_obstacles
cd models/rxi_obstacles

• Create a model.config file in the models/rxi_obstacles directory and copy the following text into the file:

<?xml version="1.0"?>
<model>
  <name>rxi_obstacles</name>
  <version>1.0</version>
  <sdf version="1.6">model.sdf</sdf>
  <author>
    <name>Your Name</name>
    <email>[email protected]</email>
  </author>
  <description>
    RXI tutorial
  </description>
</model>

• Use the program and redirection to generate the model.sdf file. This example generates a field with one of each buoy type and with the default dimensions of 40x40 m.

roscd rxi/models/rxi_obstacles
rosrun vrx_gazebo generate_avoid_obstacles_buoys --a3 1 --a5 1 --a7 1 --surmark46104 1 > model.sdf

• Review the output with more model.sdf

Now you should have both model.config and model.sdf files in the rxi/models/rxi_obstacles/ directory.

We'll need to modify the RXI ROS package so that the models are available to Gazebo.

• Edit the package.xml file so that at the end (before the closing </package> tag) the following lines are included:

  <depend version_gte="2.5.17">gazebo_ros</depend>
  <export>
    <gazebo_ros gazebo_model_path="${prefix}/models"/>
    <gazebo_ros gazebo_media_path="${prefix}"/>
  </export>

• Edit the CMakeLists.txt file, adding the following lines to the end of the file

# Install all the model files
install(DIRECTORY models/
  DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}/models)

Now you have used the Python script to generate an SDF model file (model.sdf) and included it in your RXI package. The model is available to Gazebo so you should be able to add it to your world using the methods described above. Once you have included the model in your rxi.world.xacro file, you should see something like the following.

Using the process described above, complete the following by modifying your rxi.world.xacro field:

• Generate a new randomized obstacle field with
  • 10 of the a5 buoys
  • no other buoys
  • dimensions of 10x10 m
• Position this new obstacle field model within the red/green buoys that you added previously.

When you start the simulation you should see something similar to the image below.

One component of RobotX that seems to change from year to year is the configuration of the dock structures. The docks are constructed from common building blocks, but used to create different scenarios each year. We don't know what the dock structures will look like for 2020, but we do have tools to quickly generate custom simulated dock structures from the building blocks.

The Create Custom Docks tutorial illustrates using an embedded ruby script to generate custom dock configurations based on simple text input. Work through the tutorial to come up with a custom dock shape and see if you can add it to our existing model to generate a practice world similar to the one shown below:

Detail of the dock is shown in the following image:

There is no unique solution to these tutorial tasks, but we've provided a working example of the RXI ROS package to assist in working through the tasks.

Following these steps should provide a functioning solution:

• Clone the repository in your VRX catkin workspace and make

cd ~/vrx_ws/src
git clone [email protected]:brian_bingham/rxi.git
cd ~/vrx_ws
catkin_make
source devel/setup.bash

• Start the simulation: roslaunch rxi rxi.launch verbose:=true