Simulating Heron

Whether you actually have a Heron robot or not, the Heron simulator is a great way to get started with ROS robot development. In this tutorial, we will go through the basics of starting Gazebo and Rviz and how to drive your Heron around.

Installation

To get started with the Heron simulation, make sure you have a working ROS installation set up on your Ubuntu desktop, and install the Heron-specific metapackages for desktop and simulation:

sudo apt-get install ros-melodic-heron-description ros-melodic-heron-viz ros-melodic-heron-desktop

Then install the ROS unmanned underwater vehicles simulation package:

sudo apt-get install ros-melodic-uuv-simulator

Finally, create a catkin workspace and checkout the heron_simulation package and build it:

Note

At present heron_simulation is only available from source. At a future date we will publish a debian package to allow installation through apt.

mkdir ~/catkin_ws
cd ~/catkin_ws
mkdir src
catkin_init_workspace src
cd src
git clone https://github.com/heron/heron_simulator
cd ~/catkin_ws
rosdep install --from-paths src --ignore-src
catkin_make

Launch Gazebo

Gazebo is the most common simulation tool used in ROS. Heron’s model in Gazebo include reasonable approximations of its dynamics, including inertia and buoyancy. To launch simulated Heron in a simple example world, run the following command:

roslaunch heron_gazebo heron_world.launch

You should see the following window appear, or something like it. You can adjust the camera angle by clicking and dragging while holding CTRL, ALT, or the shift key:

The window which you are looking at is the Gazebo Client. This window shows you the “true” state of the simulated world which the robot exists in. It communicates on the backend with the Gazebo Server, which is doing the heavy lifting of actually maintaining the simulated world. At the moment, you’re running both the client and server locally on your own machine, but some advanced users may choose to run heavy duty simulations on separate hardware and connect to them over the network.

Launch rviz

The next tool we will encounter is rviz. Although superficially similar in appearance to Gazebo, rviz has a very different purpose— unlike Gazebo, which shows the reality of the simulated world, rviz shows the robot’s perception of its world, whether real or simulated. So while Gazebo won’t be used with your real Heron, rviz is used with both.

You can using the following launch invocation to start rviz with a pre-cooked configuration suitable for visualizing any standard Heron config:

roslaunch heron_viz view_robot.launch

You should see rviz appear:

The rviz display only shows what the robot knows about its world, which presently, is nothing. Because the robot doesn’t yet know about the barriers which exist in its Gazebo world, they’re not shown here.

Driving Heron

What is shown, however, is Heron’s interactive markers. These are the simplest way to command your robot to move around. If you don’t see them in your rviz display, select the Interact tool from the top toolbar. You should see red arrows and a blue circle appear around the Heron model.

Drag the red arrows in Rviz to move in the linear x and the blue circle to move in the angular z. Rviz shows you Heron moving relative to its odometric frame, but it is also moving relative to the simulated world supplied by Gazebo. If you click over to the Gazebo window, you will see Heron moving within its simulated world. Or, if you drive real Heron using this method, it will have moved in the real world.

Once you start your own development, have your nodes send geometry_msgs/Twist commands to the cmd_vel topic to drive Heron, either real or simulated.