First simulation

Start one world, then add a robot or a sensor. Use two terminals with the same Ubuntu or Docker environment loaded: Terminal A runs the simulation; Terminal B inspects data.

1. Start an ocean world

In Terminal A:

ros2 launch posim_demos posim_world.launch.py \
  world_name:=posim_ocean_waves headless:=true

In Terminal B:

gz topic -e -t /world/oceans_waves/clock

Simulation time should advance. The world entity is oceans_waves, although the file is posim_ocean_waves.world. Stop the topic viewer and then the launch with Ctrl+C before starting the next example.

2. Spawn REXROV

The robot launch starts its world too; do not leave the previous world running.

ros2 launch posim_demos posim_robot.launch.py \
  namespace:=rexrov world_name:=posim_ocean_waves z:=-5 paused:=false \
  gui:=false headless:=true use_teleop:=false use_web_joystick:=false

In Terminal B:

ros2 topic echo /model/rexrov/odometry nav_msgs/msg/Odometry --once

Inspect the timestamp, pose and twist. An unmoving robot can still produce valid odometry. See ROVs to select BlueROV2 and its control interfaces.

3. Receive a camera image

Stop REXROV. Before starting the camera, confirm that a sensor renderer is available. In a container without a display, follow Docker rendering setup first: headless:=true only hides the GUI in the current launcher. Then run:

ros2 launch posim_demos posim_sensor.launch.py \
  namespace:=underwater_camera world_name:=camera_tutorial \
  x:=10 z:=-93.5 pitch:=0.3 yaw:=3.14 \
  paused:=false gui:=false headless:=true

In Terminal B:

ros2 topic echo /underwater_camera/simulated_image \
  sensor_msgs/msg/Image --once --no-arr

Check nonzero width and height, encoding and timestamp. --no-arr hides the pixel array from terminal output. To see the image, use an RViz Image display subscribed to this topic. Underwater camera explains the attenuation settings.

Desktop viewing

Open Gazebo windows on a host with a display and renderer.

• Robot/sensor launch: gui:=true headless:=false
• World launch: headless:=false

Check the results

Check these outputs from the examples.

• Advancing simulation time
• Odometry position and velocity
• Image size, format and timestamp

See ROVs for control and Multibeam sonar for sonar.

Next experiments

Try DVL, USBL, currents or the world library. First-use Fuel downloads can delay startup. If data does not arrive, inspect the advancing clock, then plugin and resource logs using Troubleshooting.

Choose launch arguments

Use --show-args to inspect arguments accepted by a robot or sensor launch.

ros2 launch posim_demos posim_sensor.launch.py --show-args

Use paused:=false in sensor examples to produce data. Inspect robot/world launch arguments with that launch's --show-args.