3D Underwater Lidar

Overview

This tutorial will launch a basic tank environment with a 3D lidar sensor mounted to a pedestal and a hovering cylindrical target.

• The sensor uses the GPURaySensor, configured to emulate the properties of 3D at Depth's SL3 underwater lidar.
• The sensor itself covers a fixed field of view but it attached to a stand that can pan and tilt.

Prerequisites

This tutorial assumes you have previously [installed the DAVE repositories](roslaunch nps_uw_sensors_gazebo uw_lidar_standalone.launch).

Launch and run the simulation

• To launch the environment, run:

roslaunch nps_uw_sensors_gazebo uw_lidar_standalone.launch

• If all goes well Gazebo should launch into a simulation environment that looks like this:

• Note that by default, the simulation is paused and no lidar rays are displayed.
• Click the play icon to unpause.
• The lidar rays will display and the sensor will pan to face the target cylinder.
• The end result will look like this:

Properties

The 3D underwater Lidar sensor has the following properties by default:

• The lidar sensor covers a 30° x 30° sector.
• It uses 145 simulated rays in each horizontal and vertical axis.
• The resolution is set to 0.1 to produce 10 data points per ray, resulting in a point cloud of 1450 x 1450 points.
• The default range is set to a maximum of 20 meters

ROS topics

The sensor outputs point cloud data to the following ROS topic:

/nps_gazebo_ros_uw/pulse_lidar/points

The plugin also publishes the following topics which are used to control the sensor stand (see Controlling pan and tilt, below):

/nps_gazebo_ros_static_lidar_robot/lidar_pan_cmd
/nps_gazebo_ros_static_lidar_robot/lidar_tilt_cmd

Visualizing with rviz

A basic rviz configuration for visualizing the plugin point cloud data is saved under nps_uw_sensors_gazebo/rviz/uw_lidar.rviz. To bring up rviz with this configuration:

1. Navigate to the root of your catkin workspace. For example:

   cd ~/uuv_ws/
   

2. Launch the simulation in Gazebo:

   roslaunch nps_uw_sensors_gazebo uw_lidar_standalone.launch
   

3. Unpause the simulation to begin generating point cloud data.
4. In a separate terminal, launch RViz using the uw_lidar.rviz configuration file. If you are running from the root of your catkin workspace, the command is:

   rosrun rviz rviz -d src/nps_uw_sensors_gazebo/rviz/uw_lidar.rviz
   

If successful, RViz should launch a separate window that looks something like this:

Controlling pan and tilt

From sdf

With rospub

rostopic pub /nps_gazebo_ros_static_lidar_robot/lidar_pan_cmd std_msgs/Float32 -- 3.14

rostopic pub /nps_gazebo_ros_static_lidar_robot/lidar_tilt_cmd std_msgs/Float32 -- 0.1