NPS Ray based Sonar

Here we examine simulating Sonar using the Gazebo GpuRaySensor sensor. We start with a single-beam plugin prototype with the expectation of expanding to offer a ray trace plugin.

Background

References

• Gazebo 9 API: http://osrf-distributions.s3.amazonaws.com/gazebo/api/9.0.0/index.html

• Gazebo 9 source code: Download Version 9.0 from http://gazebosim.org/download and unzip. Some files of interest include:

  gazebo/sensors/GpuRaySensor.cc
  gazebo/sensors/GpuRaySensor.hh
  gazebo/sensors/GpuRaySensorPrivate.hh
  plugins/GpuRayPlugin.cc
  plugins/GpuRayPlugin.hh
  

• Ros Melodic source online: https://github.com/ros-simulation/gazebo_ros_pkgs/tree/melodic-devel/gazebo_plugins.

• ROS Melodic source download: Clone gazebo_ros_pkgs and checkout branch melodic-devel:

  git clone https://github.com/ros-simulation/gazebo_ros_pkgs.git
  git checkout melodic-devel
  

  Some files of interest:

  gazebo_plugins/src/gazebo_ros_laser.cpp
  gazebo_plugins/src/gazebo_ros_gpu_laser.cpp
  gazebo_plugins/src/gazebo_ros_block_laser.cpp
  gazebo_plugins/src/gazebo_ros_range.cpp
  
  gazebo_plugins/include/gazebo_plugins/gazebo_ros_gpu_laser.h
  gazebo_plugins/include/gazebo_plugins/gazebo_ros_block_laser.h
  gazebo_plugins/include/gazebo_plugins/gazebo_ros_laser.h
  gazebo_plugins/include/gazebo_plugins/gazebo_ros_range.h
  

SDF

The SDF tag for the <ray> sensor is at http://sdformat.org/spec?ver=1.7&elem=sensor. Tag <ray> will be replaced by <lidar>. Their contents are the same:

• scan
  • horizontal
    • samples
    • resolution
    • min_angle
    • max_angle
  • vertical
    • samples
    • resolution
    • min_angle
    • max_angle
  • range
    • min
    • max
    • resolution
  • noise
    • type
    • mean
    • stddev

Horizontal and vertical scan settings are defined. For one ray trace, set vertical samples to 1. For resolution equal to sample resolution, use 1. Set min_angle, max_angle, and samples for three horizontal samples at -0.1°, 0.0°, and 0.1°.

Message

Gazebo message is C++ type ConstLaserScanStampedPtr, type gazebo.msgs.LaserScanStamped, see gazebo/msgs/laserscan_stamped.proto.

ROS message is C++ type sensor_msgs::LaserScan, see http://docs.ros.org/melodic/api/sensor_msgs/html/msg/LaserScan.html.

Single Beam Sonar

We created a single-beam Sonar based on the Gazebo ROS gazebo_ros_gpu_laser plugin. Rather than returning an array of rays, the single-beam Sonar calculates one range and intensity value based on range and intensity values in the underlying ray scan. This calculation happens in the OnScan function, see file https://github.com/Field-Robotics-Lab/nps_uw_sensors_gazebo/blob/master/src/nps_gazebo_ros_gpu_sonar_single_beam.cpp.

To build: Clone this repository under ~/uuv_ws/src (see https://github.com/Field-Robotics-Lab/dave/wiki/Install-Directly-on-Host), checkout the sonar_eqns branch, then at ~/uuv_ws type catkin_make:

cd ~/uuv_ws/src
git clone https://github.com/uuvsimulator/nps_uw_sensors_gazebo.git
cd nps_uw_sensors_gazebo
git checkout sonar_eqns
cd ~/uuv_ws
catkin_make

An alternative to cloning with https is to use the git protocol: git clone git@github.com:Field-Robotics-Lab/nps_uw_sensors_gazebo.git.

To run:

roslaunch nps_uw_sensors_gazebo sonar_single_beam_basic.launch 

Here is an example view:

To see the beam message, use rostopic echo:

rostopic echo sonar_single_beam_robot/sonar_single_beam1_sonar_range

Here is example output:

header: 
  seq: 0
  stamp: 
    secs: 42
    nsecs: 813000000
  frame_id: "sonar_single_beam_robot/sonar_single_beam_robot/sonar_single_beam1_link"
angle_min: -0.10000000149
angle_max: 0.10000000149
angle_increment: 0.10000000149
time_increment: 0.0
scan_time: 0.0
range_min: 0.10000000149
range_max: 10.0
ranges: [1.75006902217865]
intensities: [3.530477523803711]
---