Roadmap

Quick Overview of ROS1 concepts

  • Packages: Are the software organization unit of ROS code. Each package can contain libraries, executables, scripts, or other artifacts.
  • Nodes: A node is an executable that uses ROS to communicate with other nodes.
  • Messages: ROS data type used when subscribing or publishing to a topic.
  • Topics: Nodes can publish messages to a topic as well as subscribe to a topic to receive messages.
  • Master: Name service for ROS (i.e. helps nodes find each other)
  • catkin: A method for organizing and building your ROS code
  • Workspace: A working directory where all packages are stored and build with catkin

Launch Gazebo using ROS

The very first step is to create a catkin workspace if it not already exists.

mkdir -p ~/deep_ws/src
cd ~/deep_ws/
catkin_make -DPYTHON_EXECUTABLE=/usr/bin/python3

Create a package with name simulation. Here we will gather all code for launching Gazebo and loading race track worlds.

cd ~/deep_ws/src
# create package with name 'simulation' and dependency on 'gazebo_ros'
catkin_create_pkg simulation gazebo_ros
cd ../
catkin_make

After every catkin_make be sure to source your workspace!!!

. ~/deep_ws/devel/setup.bash

Gazebo in ROS has 2 nodes: gzserver and gzclient. As you remember in ROS to launch a node(script) you should first launch ROS MASTER. In order to launch both Gazebo nodes you should:

  • run roscore(ROS MASTER), gzserver and gzclient in three separate terminals
  • or make a launch file I prefer launch files. They make running ROS code so much easier. Go to deep_ws/src/simulation folder and make launch directory, in which create a file gazebo.launch. This example code launches two Gazebo nodes with the world argument, which now leads to empty world:
<!-- deep_ws/src/simulation/launch/gazebo.launch -->
<?xml version="1.0"?>
<launch>
  <arg name="world_name" default="worlds/empty.world"/>
  <node name="gazebo" pkg="gazebo_ros" type="gzserver" respawn="false" output="screen" args="$(arg world_name) "/>
  <node name="gazebo_gui" pkg="gazebo_ros" type="gzclient" respawn="false" output="screen" />
</launch>

world - is how our simulation looks, all objects, lights, shadows, etc. Empty world has nothing - only ground plane, 3-d axes and a source of light.

Now we can launch empty world in Gazebo

cd ~/deep_ws
source devel/setup.bash
roslaunch simulation gazebo.launch

empty world

That was not so difficult. Now lets load a race track world.

Load a race track world

For this task you need folders meshes, models, worlds and routes from deepracer_simapp. Download them all to deep_ws/src/simulation and create a simulation.launch file in deep_ws/src/simulation/launch folder. This launch file will include previous gazebo.launch and will pass a world argument.

<!-- deep_ws/src/simulation/launch/simulation.launch -->
<?xml version="1.0"?>
<launch>
  <arg name="world_name" default="$(find simulation)/worlds/2022_march_pro.world"/>
  <include file="$(find simulation)/launch/gazebo.launch">
    <arg name="world_name" value="$(arg world_name)"/>
  </include>
</launch>

Similarly run it from deep_ws folder with

roslaunch simulation simulation.launch

But…. wait. There is a warning:

[Wrn] [ModelDatabase.cc:340] Getting models from[http://models.gazebosim.org/]. This may take a few seconds.

Ok, it takes more than a few seconds and it seems to look for models in internet not in our simulation folder. Important: To avoid this you need to:

export GAZEBO_MODEL_PATH=$GAZEBO_MODEL_PATH:~/deep_ws/src/simulation/
export GAZEBO_RESOURCE_PATH=$GAZEBO_RESOURCE_PATH:~/deep_ws/src/simulation/

Yes, there will be another warning about folder not being a model folder etc., but it can be ignored

After path exports simulation.launch will launch a race track world. To launch other world - just change its name in file or pass it as argument in shell.

race_track

Next: Car model