tutorials Adding course elements

Overview

The vrx_gazebo package has a basic RobotX course with water, sky, coastline, and some of the challenges in fixed positions. It is easy to create your own static course or even add new challenges into a running simulation.

Prerequisites

This guide assumes you already have installed ROS and the vrx packages as covered in the setup instructions.

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Creating a world file

A world file defines the initial environment gazebo starts in, including lighting, sky, ground, and models. Let's copy one of the examples from vrx_gazebo as a starting point for our world file:

$ mkdir example_vrx_package
$ cd example_vrx_package/
$ roscp vrx_gazebo example_course.world.xacro .

Now you should have a file that looks something like this:

cat example_course.world.xacro

<?xml version="1.0" ?>
<!-- World containing sandisland model and some course challenges -->
<sdf version="1.6" xmlns:xacro="http://ros.org/wiki/xacro">
  <world name="robotx_example_course">
    <xacro:include filename="$(find vrx_gazebo)/worlds/sandisland.xacro" />
    <xacro:sandisland />

    <include>
      <uri>model://robotx_navigation_challenge</uri>
      <pose>15 0 2 0 0 0</pose>
    </include>
    <include>
      <uri>model://robotx_light_buoy</uri>
      <pose>60 0 0.25 0 0 0</pose>
    </include>
    <include>
      <uri>model://robotx_2016_qualifying_pinger_transit</uri>
      <pose>55 -50 0 0 0 -1.3</pose>
    </include>

    <!-- The 2016 dock with the three placards -->
    <include>
      <uri>model://dock_2016</uri>
      <pose>80 -8.75 0 0 0 0</pose>
    </include>

    <!-- The 2018 dock with the two placards -->
    <include>
      <uri>model://dock_2018</uri>
      <pose>120 -2.75 0 0 0 0</pose>
    </include>

  </world>
</sdf>

Notice that this is an .xacro file. If you aren't familiar with xacro files, you should read this tutorial first.

Let's go through this file and make some changes. First, notice the first two lines within the tag:

<xacro:include filename="$(find vrx_gazebo)/worlds/sandisland.xacro" />
<xacro:sandisland />

The first line imports the sandisland macro defined in vrx_gazebo. The second line calls the sandisland macro, which sets up an empty sand island environment (only water, sky, and coastline). You will likely want to include these lines in your world files unless you are simulating a location other than sandisland.

The remainder of the file is simply adding different challenges into the course. You can see a list of models / challenges included in vrx_gazebo here.

Let's add a few buoys into the world to make some obstacles to avoid. Put these lines after the other tags:

    <include>
      <!-- Small buoy found in vrx_gazebo -->
      <uri>model://polyform_a3</uri>
      <!-- X Y Z roll pitch yaw, relative to center of gazebo world (a point out in the water) -->
      <pose>-10 2 0 0 0 0</pose>
    </include>
    <include>
      <uri>model://polyform_a7</uri>
      <pose>-15 8 0 0 0 0</pose>
    </include>
    <include>
      <uri>model://surmark950400</uri>
      <pose>-12.5 -3 0 0 0 0</pose>
    </include>

Running vrx_gazebo with a custom world

Now that you have created a new world file, you can launch the simulation again with this world:

First, generate the compiled XML from the xacro file using this or another method:

rosrun xacro xacro --inorder example_course.world.xacro > my_world.world

Next, run the simulation with a custom world argument:

roslaunch vrx_gazebo sandisland.launch world:=`pwd`/my_world.world

If everything went well, you should see three new objects added into Gazebo: