map_simulator

This package provides a 2D simulator for mobile robots in ROS 2. The environment is based on a standard ROS map. Robots move through a cmd_vel topic and may publish a laser scan.

The motivation is to have a light weight simulator to demonstrate and test navigation capabilities, while using a simple map-based environment. The simulation is based on OpenCV.

Dependencies

• OpenCV
• simple_launch, installable through apt install ros-${ROS_DISTRO}-simple-launch

Running the simulation

Just launch simulation2d_launch.py by passing the map argument that should point to the yaml file of the map.

Setting map_server:=true also runs the corresponding map server.

Setting display:=false runs the simulation without display.

The Simulation node advertises a service to spawn robots in. This service is wrapped into the spawn executable.

Spawning a robot

The spawn node should be run in the same namespace as the robot_description topic. This namespace is used to publish topics.

This node takes the following arguments, which reflect the request part of a Spawn service:

• x, y, theta: where to spawn the robot
• shape: circle, square or rectangle
• radius: the radius of the robot, if circle or square (e.g. side length)
• size: 3 values as (width, length, x-offset) in case of a rectangle shape (used for display + laser detection from other robots)
• robot_color: a length-3 RGB (0-255) int array
• laser_color: a length-3 RGB (0-255) int array
• force_scanner: a Boolean (default True) to publish laser scans even if the URDF does not contain any laser scanner
• static_tf_odom: a Boolean (default False) to publish the true map -> odom frame of this robot, otherwise adds a _gt suffix
• zero_joints:a Boolean (default False) to publish 0-values for all non-fixed joints of the robot
• linear_noise and angular_noise: a float (default 0) for the standard deviation of the noise added to the robot velocity twist,

If a Gazebo laser plugin is found, the laser scans will be published with the same specifications.

If a robot is spawned twice, only the pose will be reset. If any other parameter should be changed, remove it and re-spawn it with the new configuration.

Unspawning robots

Just double-clic on the robot you want to remove. It cannot be done if display was set to False.

Robot topics

The cmd_vel topic is subscribed by the simulator, for each robot according to their namespaces.

By default, the scan topic is used to publish laser scans, unless another topic is explicitely found in the URDF as a Gazebo plugin.

Spawning an obstacle

The spawn node will spawn anything at the requested pose / size. If no robot_description topic is found, cmd_vel and scan topics will not be initialized but the spawned entity will be detected in the laser scans of other robots.

Spawning range beacons

The simulator can render range measurements between the robots and some beacons put at any (x,y) position. It relies on the sensor_msgs/Range since ROS 2 Iron (that includes a variance). For older versions of ROS 2, a similar message is defined in map_simulator.

The spawn_anchor_launch.py offers a simple way to spawn such anchors.

• the real anchor positions are given as the <name>_gt frame under /tf,
• any localization algorithm should use the <name> frame, that is at the same place as <name>_gt if publish_gt is true in spawn_anchor_launch.py. Otherwise, some range-only SLAM node should be used to estimate the positions of the anchors together with the position of the robot.

As soon as some anchors are spawned, a range topic will be published in each robot's namespace. The same topic is used for all beacons, they can be identified with the header.frame_id of the Range message.

Animating the wheels

A helper node kinematics.py is available to link the command and the current joint state, especially for bicycle / Ackermann and two-steering robots. This allows testing high-lever controllers for steering wheels robots.

This node should be run in the robot namespace and will parse the robot_description in order to identify the robot type (unicycle / bicycle / Ackermann / two-steering) from the topology of the joints. The node will publish the corresponding joint_states in order to animate the wheels.

The sampling time can be set from the parameter dt (default 0.1 s).

Unicycle robots

The node will simply subscribe to cmd_vel and publish the corresponding angle of the wheels. It will set the (b, r) parameters to the baseline and wheel radius parsed from robot_description.

Steering wheels

• Bicycle or Ackermann-like: the node will subscribe to cmd and expects ackermann_msgs/AckermannDrive messages
• Two steering wheels: the node will subscribe to cmd and expects four_wheel_steering_msgs/FourWheelSteering messages

Ackermann-like robots will be added a dummy joint called steering that represents the actual steering angle.

• Parameters:
  • pub_cmd (default True) to publish the corresponding cmd_vel, subscribed by map_simulator
  • use_angle_cmd (default True) to take into account the steering_angle setpoint from the message
    • if use_angle_cmd is False or steering_angle is NaN, steering_angle_velocity is considered as a setpoint
    • otherwise, steering_angle_velocity is considered as the maximum rate to reach the steering_angle setpoint

The node will also set (L, r) parameters that are the wheel distance and radius parsed from robot_description.

Examples

Examples require slider_publisher and simple_launch packages:

sudo apt install ros-$ROS_DISTRO-slider-publisher ros-$ROS_DISTRO-simple-launch

Multi robot with 3 R2D2

The example/multirobot folder shows how to run a simulation and spawn 3 robots. Sliders allow controlling the robots manually. Defaut laser scanners are simulated as the robots do not have any in the URDF.

ros2 launch map_simulator multi_launch.py

Turtlebot world

The example/turtlebot3 folder shows how to run a simulation and spawn a Turtlebot3 in the classical turtlebot world. Sliders allow controlling the robot manually.

In this case the URDF has a laser scanner (as Gazebo plugin) and the corresponding properties are used.

If sim_wheels is True then an additional node changes cmd_vel into current wheel angles.

ros2 launch map_simulator turtlebot3_world_launch.py