# 3. Problem domain: Traffic network of Dubins cars¶

Often referred to as “the second domain,” the basic setting is navigation in a small network of roads with vehicles that follow unicycle-like dynamics. Every road network is a 4-connected grid, subject to a rigid-body transformation: as such, the segments may not be axis-aligned.

## 3.1. Preparations¶

While below we include pointers to the main websites for dependencies, many are available via packages for your OS and may already be installed, especially if you have ROS on Ubuntu 14.04. Supported platforms are described in the Introduction.

### 3.1.1. Basic¶

There are two major variants of this benchmark: one based in simulation and another on a physical testbed. We begin with preparations appropriate for both.

On Ubuntu, Eigen can be obtained by installing the “libeigen3-dev” deb package (https://packages.debian.org/jessie/libeigen3-dev).

Several ROS packages for the Kobuki by Yujin Robot are required.

Install fmrb from your copy of the repository, e.g.,

cd tools/fmrb-pkg
pip install -e .

pip install fmrb


(forthcoming)

### 3.1.4. Supplementary prerequisites¶

As for the Problem domain: Scaling chains of integrators, there is code that is relevant but not required for this benchmark.

Teleoperation of the vehicle to be controlled can be achieved using kobuki_keyop ROS package. An example demonstrating a configuration known to work in the simulation variant:

roslaunch dubins_traffic_utils teleop.launch


## 3.2. Tutorials¶

In the below code, $FMRBENCHMARK is the absolute path to a copy of the fmrbenchmark repository on your machine. ### 3.2.1. Demonstrations of components¶ To build the “standalone” (i.e., independent of ROS) examples demonstrating various parts of this benchmark, go to the dubins_traffic_utils directory ($FMRBENCHMARK/domains/dubins_traffic/dubins_traffic_utils) and then follow the usual CMake build instructions. On Unix without an IDE, usually these are

mkdir build
cd build
cmake ..
make


One of the resulting programs is genproblem, the source of which is $FMRBENCHMARK/domains/dubins_traffic/dubins_traffic_utils/examples/standalone/genproblem.cpp. The output is a problem instance in JSON. To visualize it, try dubins_traffic_utils/build/genproblem dubins_traffic_utils/examples/trialsconf/mc-small-4grid-agents2.json | analysis/plotp.py -  from the directory $FMRBENCHMARK/domains/.

### 3.2.2. Launching a problem instance of the simulation variant¶

Create a catkin workspace.

mkdir -p dubsim_workspace/src
cd dubsim_workspace/src
catkin_init_workspace


Create symbolic links to the ROS packages in the fmrbenchmark repository required for this example.

ln -s $FMRBENCHMARK/domains/integrator_chains/integrator_chains_msgs ln -s$FMRBENCHMARK/domains/dubins_traffic/dubins_traffic_msgs
ln -s $FMRBENCHMARK/domains/dubins_traffic/dubins_traffic_utils ln -s$FMRBENCHMARK/domains/dubins_traffic/dub_sim
ln -s $FMRBENCHMARK/domains/dubins_traffic/e-agents/wander ln -s$FMRBENCHMARK/examples/dubins_traffic_examples


Build and install it within the catkin workspace.

cd ..
catkin_make install


Because the installation is local to the catkin workspace, before beginning and whenever a new shell session is created, you must first

source install/setup.zsh


where the source command assumes that you are using the Z shell; try setup.bash if you use Bash.

Finally, launch a small 4-grid road network with two adversarially controlled vehicles, also known as e-agents (where e’’ abbreviates environment’‘).

python $FMRBENCHMARK/domains/dubins_traffic/trial-runner.py -f mydata.json$(rospack find dubins_traffic_utils)/examples/trialsconf/mc-small-4grid-agents2.json


This will cause trial data to be saved to the file mydata.json in the local directory from where the above command is executed.

The Gazebo server is launched without a GUI frontend, which is also known as running headless. A local viewer can be launched using

gzclient


The vehicle to be controlled has the ROS namespace /ego. The e-agents have namespaces defined in the trials configuration file. In the example mc-small-4grid-agents2.json used in this tutorial, these are /agent0 and /agent1.

In a separate terminal, run your controller. For example, assuming your controller is contained in the package your_controller with launch file foo.launch, in a separate terminal, run

roslaunch your_controller foo.launch


You can run an example controller using:

roslaunch dubins_traffic_examples simple.launch


This is a simple controller that sets the ego vehicle’s forward and angular velocity based on the next goal to be visited, and cycles through goals in this manner.

Support code for working with road network descriptions is available in roadnet.hpp and dubins_traffic.py.

For example, try

analysis/plotp.py dubins_traffic_utils/examples/data/square.json


from the directory \$FMRBENCHMARK/domains/dubins_traffic/.