ENHANCEMENT OF THE NAVIGATION DATA QUALITY …hochschule-bochum.de/fileadmin/media/fb_v/labore/photogrammetrie/6... · DATA QUALITY OF AN AUTONOMOUS FLYING UNMANNED AERIAL VEHICLE

© 2014 – Bochum University of Applied Sciences

ENHANCEMENT OF THE NAVIGATIONDATA QUALITY OF AN AUTONOMOUSFLYING UNMANNED AERIAL VEHICLEFOR USE IN PHOTOGRAMMETRY

Heinz‐Jürgen PrzybillaManfred Bäumker, Alexander Zurhorst


Content

Introduction Technical aspects of the Mikrokopter system Examination of positioning sensors

– Actual status of positioning quality using low‐cost GPS sensors

– Enhancements of positioning quality

Photogrammetric applications Conclusions


Introduction

Nowadays Unmanned Aerial Vehicles/Systems (UAV/UAS) are beyond the stage of testing.

Since 30 years they have been used for a wide spectrum of applications.


History…1979/80

Schlüter Photohelicopter

Pilot andNavigator


History…1979/80

First Tests

Hamburg ISP‐Congress 1980


History…1979/80

Above: Archeologicaldocumentation, CologneLeft: North Sea tideland


Introduction

Reasons for this fact are the enormous developments in consumer‐electronics needed for the operating of a copter, available in conjunction with low fees.

The „MikroKopter“ system is developed under the assistance of an internet community.

All electronic components used are standard products, fixed together to an efficient and low‐prize UAV.


Introduction

The main focus for using the copter at HS BO are photogrammetric applications.

These requirements derive the enforcement of high quality images and precise nagivation.

Actually a typical GPS‐sensor (used in low‐cost systems) achieves a differential GPS quality of• 1‐2m in horizontal and• 3‐5m in vertical direction


Introduction

Aims of the investigation: Enhancing GPS‐navigation by implementing a realtime kinematic GPS solution.

Testing of alternative photogrammetric techniquesfor image orientation and processing.


The Mikrokopter Project

Completely documented under the Web Site www.mikrokopter.de .

A matter of do‐it‐yourself project. Actually three MikroKopter systems are available for the investigations: – an Oktokopter of the HS BO and – a Hexakopter and a Hexakopter XL of the project partner Aerometrics (www.aerometrics.de).


The Mikrokopter ProjectParameter Value

Number of rotors:

4 – 12

Actual load: 250 g – 1000 g

Weight: 650 g – 1700 g

Flying time: 7 – 12 min

Distance: Visual range

Flying height: Max. 350 m (technically reliable)

Power supply: Lipo 11,1 V – 14,8 V

Sensors: Gyroscopes, accelerometers, compass, GPS, barometric altimeter


Sensors

GPS-Module

Navi-Control

Flight-Control

Telemetry-ModuleBrushless-Controller


Mikrokopter ‐ Flightcontrol3 MEMS-GyrosADXR 610

Air pressure sensor MPX4115A

3-axis accelerometer

LIS344 ALH


Camera (Ricoh GXR)


Aerial flight with operating altitude of 100m

Camera: Ricoh GXR, f=18mm)


Aerial flights with operating altitude of 50m



Oblique image of an electric tower



Examinationof Positioning Sensors u‐blox GPS receiver: LEA‐6S/6T

(horizontal positioning information) 50 channels (GPS‐L1/CA‐Code, GALILEO OS). SBAS‐option (satellite based augmentation system) to

acquire the correction signals of WAAS, EGNOS or MSAS.

At the Bochum location signals of the two EGNOS (European Geostationary Navigation Overlay System) satellites Inmarsat AOR‐E and IOR‐W are available and used to calculate a differential GPS position.


Examinationof Positioning Sensors

u‐blox receivers as part of the GPS circuit board. Left: board surrounded by a protection shield to enhance GPS signal


FlightcontrolFlightdata (Position, Height, Speed, Camera-triggering etc.) via 868 MHz-

Telemetry

Realtime-image via 5.8 GHz-transmitter with tracking antenna –

usable for FPV-flight with video-glasses

(FPV = First Person View)

Ground Station


Testfeld Hochschule Bochum

5700780

5700800

5700820

5700840

5700860

5700880

5700900

5700920

32379900 32379920 32379940 32379960 32379980 32380000 32380020

Easting

North

ing

Passpunkt

23 Reference-points ETRS89

Signalisation with air visibletargets

Systemtest at HS Bochum Testfield



Tracking TachymeterTrimble S6


Miniprism fixed on camera-frame for automatic tracking with Trimble S6



GPS Capability Approval

To check the performance of the GPS‐sensor diverse test were carried out: Long term measurements at a reference station (static)

Short term measurements at known ground control points (static)

Short term measurements during flight over a known ground control point (dynamic)

Aerial flights with operating altitude of 50m and 100m (dynamic)


Short term measurements during flight over a known GCP (dynamic*)

* Copter‐Tracking with tachymeter Trimble S6


Aerial flight with operating altitude of 50m (dynamic)


The quality of positioning varies with a mean deviation from 3 – 4 m, not considering some outliers of more than 10 m.

As a consequence of these effects the planned overlapping of adjacent images often exceeds a tolerable limit.

Actual status of positioning quality


Solution: integration of high performance GPS positioning using real‐time kinematic (RTK) technologies.

Requirements: Availability of an appropriate GPS‐receiver and of an applicabale software system

These requisitions could be met.

Enhancements of positioning quality


Equipment used for presented test:– One‐frequency receiver of u‐blox series (LEA‐6T) in combination with an own reference station

– RTK‐calculations performed with RTKLIB, an open sourceprogram package for GNSS positioning

Under way are tests with a two‐frequency receiver(however it is much more expensive, with a priceratio of 140€ : 2500€)



Distributed free of charge under GNU GPL v3‐license.

It supports standard and precise positioning algorithms with GPS, GLONASS, SBAS, GALILEO (which is enabled but not supported in current version) and QZSS (Japan).

Various positioning modes with GNSS for both real‐time and post‐processing (Single‐point, DGPS/ DGNSS, Kinematic, Static, Moving‐baseline etc.).

RTKLIB Features


A wide range of standard formats and protocols for GNSS can be processed, like RINEXi, RTCMx, as well as the proprietary messages of several GNSS receivers.

The external communication interface supports serial, TCP/IP, NTRIP and FTP/HTTP protocols.

All in all RTKLIB is a high‐tech solution and predestinated for a low‐cost UAV‐system.

RTKLIB Features


The u‐blox raw‐data are sent to the ground control station via telemetry.

Realtime calculations of the RTK‐solutions are carried out with RTKLIB.

(Raw‐data of the UAV u‐blox as well as those of the reference station are stored for additional post‐processing.)

RTK‐positions are transferred back to the UAV flight‐control via telemetry.

Test scenario “Autonomous RTK‐Flight”



Reference station with JAVAD Triumph‐1 G3T (left). RTKLIB screenshot (right)



Accuracy of realtime calculations with RTKLIB while positioning the u‐blox sensor at the test field

red: single GPS‐solution: 5 m – 20 morange: float‐solution: 0.1 m – 1.0 mgreen: fixed‐solution: 0.02 m – 0.1 m (first test: 90% of time)


With the exception of the initiation phase (lasting 30 seconds) the RTK processing software calculates either a fixed solution or a float solution.

Instead of an own references station it is possible to use the data of a foreign reference station or a reference service like the German SAPOS HEPS‐Service.

Suitable tests will be carried out in the next weeks.



Conclusions

Navigation accuracy is a critical parameter for a successful operation of UAVs.

The actual DGPS accuracies have to be improved. RTK‐GPS is a usable technology but requires further technical developments.

A partial direct georeferencing for UAV sensors (concerning their position in space) is realisable.


Conclusions

Aerial flight with UAVs – in context with classicalimage overlapping – suffers from insufficientnavigation quality.

As a result the overlapping ratio has to beincreased considerably.

Recently available software products for theorientation of „large unordered image collections“ show encouraging results in generating spatialpoint clouds with „pleasant“ geometric quality.

Documents

ENHANCEMENT OF THE NAVIGATION DATA QUALITY …hochschule-bochum.de/fileadmin/media/fb_v/labore/photogrammetrie/6... · DATA QUALITY OF AN AUTONOMOUS FLYING UNMANNED AERIAL VEHICLE