Flight path planning system for autonomous unmanned aerial vehicles

125 Pages·2004·2.08 MB·English

Flight path planning system
for autonomous unmanned
aerial vehicles
Jarle An(cid:28)nsen
Leif Hamang Bru
November 2004
Project report in
TDT4715 Algorithm construction
and visualization, specialization
Supervised by Prof. Bjłrn Olstad
Faculty of Information Technology, Mathematics and Electrical Engineering
Department of Computer and Information Science

Abstract
Unmanned Aerial Vehicles (UAVs) have a tremendous appeal. One can imag-
inealargenumberofapplicationssuchassearch-and-rescue,tra(cid:30)cmonitoring,
aerialmapping, etc. HelicoptersareparticularlyattractiveduetotheirVertical
Take O(cid:27) and Landing (VTOL) capabilities. The research on UAVs has shown
rapid development in recent years, and o(cid:27)ers a great number of research chal-
lenges. Aconsiderablepartofpreviousresearchhasfocusedonlow-levelcontrol
capabilities. But the focus is shifting from low-level control to a combination of
low-levelanddecision-levelcontrol. Thisreportistheresultofaprojectwhichis
apartoftheAutonomousRemoteControlledHelicopter(ARCH)projectatthe
Department of Computer and Information Science at the Norwegian University
of Science and Technology.
The object of this project is divided into two main sections. Firstly, it is to
create and describe an API and a communication protocol to support the com-
municationbetweenthelow-levelandthedecision-levelcontrollerintheARCH
project. Secondly, it is to propose a solution to a (cid:29)ight path planner, which
is capable of solving the total coverage problem. In solving the total coverage
problem, the path planner should be able to take into account considerations
such as light conditions and resource usage. This will make it applicable to
mission tasks such as aerial photography.
AnextensibleAPIforcommunicatingwithanautonomousunmannedhelicopter
is presented. An algorithm for de(cid:28)ning (cid:29)ight paths for a (cid:29)eet of cooperating
unmannedhelicoptersaimingtoachieveoptimalsensorcoveragewhileavoiding
collisions and minimizing resource usage has been proposed. A prototype path
planner application is developed in order to test the proposed solution.
The prototype shows that the proposed system produces high quality (cid:29)ight
paths within reasonable time limits. Therefore, the main contribution of this
project work is an o(cid:31)ine UAV system blueprint for the ARCH project.
i

Preface
Thisisthereportonastudyconductedbytwocomputersciencemajorstudents
attheDepartmentofComputerandInformationScience(IDI)attheNorwegian
University of Science and Technology (NTNU). The project’s period was from
the16thofAugusttothe26thofNovember. TheprojectwassupervisedbyProf.
Bjłrn Olstad and Post.doc. Will Archer Arentz from the NTNU. This study
is a part of the Autonomous Remote Controlled Helicopter (ARCH) project at
IDI,NTNU.TheARCHprojecthasalreadygainedpublicinterest,whenitwas
featured on a television program (Schr(cid:246)dingers katt, NRK. September 2004).
The(cid:28)rstthreechaptersprovidebackgroundinformationaboutthisprojectand
unmanned aerial vehicles in general. It also describes an API developed to
support communication between autonomous unmanned helicopters and client
applications. Chapterfourprovidesatheoreticalfundamentfor(cid:29)ightpathplan-
ningforunmannedaerialvehicles,whilechapter(cid:28)vedescribesthepathplanners
proposed in this project. Thus, chapter two to six are basically separated into
two parts, where the (cid:28)rst two chapters covers the communication part of the
proposedsystemandthetwolastchapterscoversthepathgenerationpartofthe
system. Chapter six contains discussions about the strengths and weaknesses
of the solutions proposed in this project. In the (cid:28)nal chapter, conclusions are
drawn based on the previous chapters, and future work is proposed.
It has been assumed that the reader has a basic knowledge of computer science
and mathematics. Basic knowledge of common algorithmic strategies is also
assumed. Concepts in viewshed and path generation are explained where the
understanding of these concepts are necessary to understand other parts of the
report. Concepts that are less central are not explained, but the reader is given
referencesthatenableshim/hertolearntheseconceptsfromothersources. This
explanationofcommonconceptsisnecessaryforthereporttobereadbypeople
from all (cid:28)elds interested in the research of unmanned aerial vehicles and path
generation.
iii

Acknowledgements
We would like to thank our supervisors, Prof. Bjłrn Olstad and Post.doc. Will
Archer Arentz at IDI, NTNU, for tutoring us through this project, especially
Will for answering numerous questions. In addition, we would like to thank Jo
Vetle Aure Hansen and Fredrik Orderud for contributing.
v

Contents
Contents 1
1 Introduction 5
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Autonomous aerial vehicles 7
2.1 Potential of autonomous (cid:29)ying vehicles . . . . . . . . . . . . . . . 7
2.1.1 What is a UAV . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.2 The usage of UAVs . . . . . . . . . . . . . . . . . . . . . . 10
2.1.3 Aerial photography . . . . . . . . . . . . . . . . . . . . . . 13
2.2 ARCH - Autonomous Remote Controlled Helicopter . . . . . . . 14
2.2.1 Hardware platform . . . . . . . . . . . . . . . . . . . . . . 14
2.2.2 Software platform . . . . . . . . . . . . . . . . . . . . . . 15
2.2.3 Software requirements . . . . . . . . . . . . . . . . . . . . 15
3 ARCH task speci(cid:28)cation system 17
3.1 UAV control architectures . . . . . . . . . . . . . . . . . . . . . . 17
3.2 The ARCH API and communication protocol . . . . . . . . . . . 18
3.2.1 The ARCH API . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.2 The ARCH communication protocol . . . . . . . . . . . . 23
3.2.3 Implementation . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 ARCH GroundStation . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3.1 Functional description . . . . . . . . . . . . . . . . . . . . 24
3.3.2 Architectural description . . . . . . . . . . . . . . . . . . 27
1
2 CONTENTS
4 Flight paths for UAVs 31
4.1 DEM - Digital Elevation Map . . . . . . . . . . . . . . . . . . . . 32
4.2 Path generation techniques . . . . . . . . . . . . . . . . . . . . . 33
4.2.1 Path generation using heuristic search methods . . . . . . 33
4.2.2 Other path generation techniques . . . . . . . . . . . . . . 38
4.3 Sensor coverage calculation . . . . . . . . . . . . . . . . . . . . . 40
4.3.1 Viewshed computation . . . . . . . . . . . . . . . . . . . . 41
4.3.2 Approximating viewshed and visibility . . . . . . . . . . 45
4.4 Bringing the sun into the equation . . . . . . . . . . . . . . . . . 46
4.4.1 Finding the sun . . . . . . . . . . . . . . . . . . . . . . . . 46
4.4.2 Latitude Longitude Altitude (LLA). . . . . . . . . . . . . 48
4.4.3 Earth-Centered, Earth-Fixed (ECEF) . . . . . . . . . . . 50
4.4.4 Northing Easting Down (NED) . . . . . . . . . . . . . . . 52
4.4.5 Calculating the sun angle at a given position . . . . . . . 52
5 UAV path planners for the ARCH project 55
5.1 Calculating viewshed . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2 Finding the best observation points . . . . . . . . . . . . . . . . . 60
5.3 Finding the best Hamiltonian paths . . . . . . . . . . . . . . . . 64
5.3.1 The simulated annealing approach . . . . . . . . . . . . . 64
5.3.2 The minimum spanning tree approach . . . . . . . . . . . 68
5.4 Finding intersections between paths . . . . . . . . . . . . . . . . 71
5.4.1 Bounding Boxes . . . . . . . . . . . . . . . . . . . . . . . 71
5.4.2 Unions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.5 Smoothing the (cid:29)ight paths. . . . . . . . . . . . . . . . . . . . . . 73
5.5.1 Creating splines . . . . . . . . . . . . . . . . . . . . . . . 73
5.5.2 Avoiding collision . . . . . . . . . . . . . . . . . . . . . . . 75
5.6 Locating obstacles at operating altitude . . . . . . . . . . . . . . 76
5.6.1 Preprocessing . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.6.2 Locating objects . . . . . . . . . . . . . . . . . . . . . . . 77
5.6.3 Representing objects . . . . . . . . . . . . . . . . . . . . . 77
5.6.4 Checking a path . . . . . . . . . . . . . . . . . . . . . . . 78
5.7 Finding collision-free paths between waypoints . . . . . . . . . . 79
5.8 Single UAV path planners . . . . . . . . . . . . . . . . . . . . . . 82