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UVDAR drivers and processing

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Description

This package contains the core signal processing and pose estimation software components of the UVDAR system necessary for running it on a MAV.

  • the UVDAR system is a visual mutual relative localization system for cooperating micro-scale UAVs
  • based on ultraviolet-sensitive cameras and blinking ultraviolet markers
  • can be used both indoors and outdoors without infrastructure
  • robust to a variety of lighting conditions

System requirements

Hardware:

  • One or more calibrated (Using the OCamCalib model) grayscale camera sensors with ultraviolet bandpass filters. In our setup these are:

    • mvBlueFOX MLC200wG cameras
    • Sunnex DSL215 lenses with ~180 degrees of horizontal FOV
    • Midopt BP365-R6 filters with our custom holder between the sensor and the lens

  • Blinking ultraviolet LEDs (395nm) attached to extreme points of the target UAVs. In our setup, these are:

    • ProLight Opto PM2B-1LLE
    • Attached to the ends of the arms of the UAVs %% * , respectively on the top of the UAVs for "beacons"
    • For quadrotors, the markers comprise two LEDs each, rotated 90° from each other in the "yaw" axis of the UAV

  • Blinking signal generator

Software

  • ROS (Robot Operating System) Melodic Morenia
  • mrs_lib - ROS package with utility libraries used by the MRS group
  • mrs_msgs - ROS package with message types used by the MRS group
  • mrs_serial - ROS package implementing serial communication with LED drivers
  • bluefox2 - ROS package providing interface with mvBlueFOX cameras

For testing in simulation

  • mrs_uav_system - Our ROS-based ecosystem for flying and testing multi-UAV systems
  • uvdar_gazebo_plugin - Emulation library that produces meta-data that is used for generation of synthetic UV LED image stream in simulation

Installation

  • Install the dependencies.
  • Clone this repository into a ROS workspace as a package.
  • Run install/install.sh
  • Build the package using catkin tools (e.g. catkin build uvdar_core)

Testing

In order to test the system in simulation, install all software dependencies including those designated for testing in simulation (Above) and run this script in the scripts folder: %% * For testing separation of units based on position and beacons use beacon_test.sh %% * For testing separation of units based on different blinking frequencies multi_frequency_test.sh

Note, that the script slows down the simulation below real-time. This is necessary, since if Gazebo slows down automatically due to insufficient processing power, the blinking signals get corrupted. Test the maximum admissible real-time factor for your computer by checking how far you can increase / have to decrease it such that the real-time factor consistently stays at the value it was set to.

Node description

The package comprises multiple ROS nodes (N) and nodelets (n):

  • UVDARDetector - n - detects bright points from the UV camera image. These are used as candidates for UV LED markers. Current implementation uses GPU acceleration.

  • UVDARBlinkProcessor - n - Extracts blinking signals and image positions of the markers detected previously

  • UVDARPoseCalculator - N - Calculates approximate pose and error covariances of the MAVs carrying the UV LED markers. Note, that this is an example for the specific layouts on quadrotors and hexarotors we use. If you need a different layout, you will also need to write your custom pose calculation

  • UVDARKalman - N - Filters out sets of detected poses with covariances based on positions or the included identities. This filtering occurs in a selected coordinate frame

  • UVDARBluefoxEmulator - n - Generates an image stream similar to the output of our Bluefox cameras with UV bandpass filters (above). This image is currently rudimentary, with background of a constant shade of grey and white circles where the markers appeared. The function of this node depends on our uvdar_gazebo_plugin, with which it needs to communicate

  • LedManager - N - Sends commands to our controller boards that set the signals of the blinking UV LEDs on the current MAV using the Baca Protocol. You can command this node using ROS services. This is loaded using led_manager.launch.

Releavant papers

V Walter, N Staub, A Franchi and M Saska. UVDAR System for Visual Relative Localization With Application to Leader–Follower Formations of Multirotor UAVs. IEEE Robotics and Automation Letters 4(3):2637-2644, July 2019. 
@article{uvdar_dirfol,
	author = "V. {Walter} and N. {Staub} and A. {Franchi} and M. {Saska}",
	journal = "IEEE Robotics and Automation Letters",
	title = "UVDAR System for Visual Relative Localization With Application to Leader–Follower Formations of Multirotor UAVs",
	year = 2019,
	volume = 4,
	number = 3,
	pages = "2637-2644",
	doi = "10.1109/LRA.2019.2901683",
	issn = "2377-3766",
	month = "July",
	pdf = "data/papers/walterRAL2019.pdf"
}
V Walter, M Vrba and M Saska. On training datasets for machine learning-based visual relative localization of micro-scale UAVs. In 2020 IEEE International Conference on Robotics and Automation (ICRA) (). August 2020, 10674-10680. 
@inproceedings{walter_icra2020,
	author = "V. {Walter} and M. {Vrba} and M. {Saska}",
	booktitle = "2020 IEEE International Conference on Robotics and Automation (ICRA)",
	title = "On training datasets for machine learning-based visual relative localization of micro-scale {UAVs}",
	year = 2020,
	volume = "",
	number = "",
	month = "Aug",
	pages = "10674-10680",
	pdf = "data/papers/walter2020_icra.pdf"
}
V Walter, N.Staub, M Saska and A Franchi. Mutual Localization of UAVs based on Blinking Ultraviolet Markers and 3D Time-Position Hough Transform. In 14th IEEE International Conference on Automation Science and Engineering (CASE 2018). 2018. 
@inproceedings{uvdd2,
	author = "V. Walter and N.Staub and M. Saska and A. Franchi",
	title = "Mutual Localization of UAVs based on Blinking Ultraviolet Markers and 3D Time-Position Hough Transform",
	booktitle = "14th IEEE International Conference on Automation Science and Engineering (CASE 2018)",
	pdf = "data/papers/uvdd2.pdf",
	year = 2018
}
V Walter, M Saska and A Franchi. Fast mutual relative localization of uavs using ultraviolet led markers. In 2018 International Conference on Unmanned Aircraft System (ICUAS 2018). 2018. 
@inproceedings{uvdd1,
	author = "V. Walter and M. Saska and A. Franchi",
	title = "Fast mutual relative localization of uavs using ultraviolet led markers",
	booktitle = "2018 International Conference on Unmanned Aircraft System (ICUAS 2018)",
	pdf = "data/papers/uvdd1.pdf",
	year = 2018
}

Acknowledgements

MRS group

This work would not be possible without the hard work, resources and support from the Multi-Robot Systems (MRS) group from Czech Technical University.

Included libraries

This package contains the following third-party libraries by the respective authors:

  • OCamCalib calibration system by Davide Scaramuzza - only the C++ sources are included here. To perform calibration of the UV-sensitive cameras, use This modification of the toolbox.