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Geomatics PhD school, Finland, 2011 1 Vienna University of Technology Institute of Photogrammetry and Remote Sensing Norbert Pfeifer

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Page 1: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 1

Vienna University of Technology  Institute of Photogrammetry

and Remote

Sensing

Norbert Pfeifer

Page 2: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 2

Geomatics on the move

• to moving

measurement

platforms

• from

single

to multi‐sensor

systems

• to higher

autonomy

and automation

• to new

fields

of applications

Page 3: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 3

Today‘s program

• 9:00 ‐

9:45 

Experiences from assembling and operating a UAV

• 9:45 ‐

10:15 

A UAV application in ecology

• 10:15 ‐

10:30

Discussion

• 10:30 ‐

11:00 

Break

• 11:00 ‐

12:30 

Lidar

introduction

and beyond

• 12:30 ‐

13:30 

Lunch break

• 13:30 ‐

14:00 

Lidar

on UAVs

survey

(only

15‘)

• 14:00 ‐

15:00 

Lidar

point clouds

and their

use

in vegetation

mapping

• 15:00 ‐

15:30 

Break

• 15:30 ‐

16:45 

Lidar

point clouds

for

geomorphology

• 16:45 ‐

17:00 

Discussion

but with morebreaks

Page 4: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 4

TU Wien

• Vienna University of Technology• Mission “technology for

people”

• 23,000 students, 5000 academics• Faculties

– Mathematics

and Geoinformation– Physics– Informatics– Electrotechnical

Engineering– Civil Engineering– Architecture

and Spatial

Planning– Mechanical

Engineering– Chemistry

• Geoinformation institutes– Photogrammetry

and Remote

Sensing– Geodesy

and Geophysics– Geoinformation and Cartography

Page 5: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 5

Institute of Photogrammetry and Remote

Sensing

I.P.F.

Prof. W. Wagner (Head), Professor in Remote Sensing• Radar Remote

Sensing

• Physical

aspects

of Laser ScanningProf. N. Pfeifer, Professor in Photogrammetry• Photogrammetry• Geometrical

aspects

of Laser Scanning

Assoc. Prof. J. Jansa• Optical

Remote

Sensing

• Digital Image ProcessingStaff: ~50 (incl. ~12 faculty staff)• Geodesists, geographers, 

environmental

engineers,  physicists, 

computer

scientists

5

Page 6: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 6

Assembling and operating a UAV

Christian BriesePhilipp Glira

Norbert Pfeifer

Institute of Photogrammetry and Remote

Sensing

Vienna University of Technology

Page 7: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 7

Assembling and operating

a lightweight

UAV

• Overall goal Direct

georeferencing

of UAV imagery

using

on‐board

components

• Secondary

goal−

learn

about

UAVs

enter

geomatic

UAV research

• Why? / Motivation−

Georeferencing

UAV

Specific

field

of applications

• How?−

Photogrammetric

Theory

Navigation

Electronics etc.

• How

precisely? / Combating

problems

Page 8: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 8

Motivation: direct georeferencing

Georeferencing• Each

sensor

measures

in its

own

sensor

coordinate

system. • Transformation between

sensor

coordiante

system

and superior coordinate

(reference) system

has 

6 independent parameters:  exterior

orienation

(pose, position

and angular

attitude, …)• Indirect

georeferencing: Using

control

points

(reference

frame)  and the

observation

equations

from

the

sensor

(collinearity,  range, …) the

exterior

orientation

of the

sensor

coordinate

system can

be

estimated.   Kraus, 2004. Photogrammetrie, Dümmler.

Page 9: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 9

Georeferencing

Georeferencing

• Direct

georeferencing: using observations

from

other

(additional) measurement devices, the

exterior

orientation

of the

sensor

can be

„directly“

observed.

ikv

working

group

at the

Institut für Geodäsie der 

Universität der Bundeswehr, Munich

Heine, 2004. Hydrografische Vermessung von 

Gewässersohlen von kleinen und mittelgroßen 

Page 10: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 10

Direct georeferencing: pros+cons

• Independent observation– not

affected

by

insufficient

sensor

model

(calibration)

– not

affected

by

gross

errors

in sensor

measurements

• Precision

not

necessarily

fits

to measurement precision

of sensor

• Reliability: redundancy may be low (GNSS/INS)

• Mounting

and possibly

other as additional unknowns

(constant?)

Kraus, 2004. Photogrammetrie, Dümmler.

Page 11: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 11

Direct georeferencing: pros+cons

Figure: Optech

• Indirect

georeferencing

not

always possible

or

feasible

– too

low

redundancy

(no control

points)– dynamic

aquisition

= individual

exterior

orientation

for

each

sensor

measurement– Singularity

in system

of observation

equations

(image taken

over

flat

scene, …)

• Direct

georeferencing

method

needs

to be

adapted

to  environment

(indoor

positioning, etc.)

• Additional costs

and complexity

because

of additional  sensors

• Bundling

sensor

and direct

georeferencing

on one platform

can

increase

efficiency

(ease

of deployment, 

speed

of delivery, …)

Page 12: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 12

Georeferencing

• Integrated

georeferencing

is

optimal (provides

exterior

orientation

with

best 

accuracy

and reliability)

• One step

after

the

other

• Direct

georeferencing

of UAV

imagery

Page 13: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 13

Motivation: UAVs• Get

airborne

yourself

(small

costs, little

expertise, …)

• High resolution: low

flying

height

• Deployment: easy

and fast

• Access areas

forbidden

or dangerous

for

humans

• Drawback: missing

legal framework

• Drawback: reduced

human reasoning

in crash situations

• Drawback: limited

payload

for

small

UAVs

• Question: which

UAV ? 

www.nanokopter.at

Page 14: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 14

UAV: balloons

• Simple to build, cheap, long

endurance

• Affected

by

wind, bulky, cumbersome

to maneuver, number of people

required

(Vierling, 2006)

(Sanswire, 2007)

(Cheng, 2006)

(USCG, 2008)

Page 15: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 15

UAV: micro‐planes

• Up to 500m a.g.l., very

small, low

noise

level

(sound)

• Small payload, high speed

required, short

flight

time, expensive

(Cyberflight, 2006 )

(Us Air Force, 2006))

(Tamblyn, 2003 )

(Israel Aircraft, 2003 )

Page 16: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 16

UAV: large span planes

• Own

weight: ~0.5kg, windspan>0.5m, long

endurance,  autonomous

flying, larger payload, low

noise

• Forbidden

in most

countries, take‐off

and landing

(Cropcam)

(Aerosonde)

(Skylarc)

Page 17: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 17

UAV: unmanned helicopters

• Available

in all sizes, easy

to fly

and to transport, payload according

to size, simple start and landing

• vibrations

(Yamaha) (Aeroscout)

(Schiebel)

(Micro Flying Robot, 2003)

Page 18: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 18

UAV: motorized parachutes

• Up to 5000m a.g.l., very

long

endurace

(2 days), high  payload, slow

but

stable

flight

• Compicated

take‐off, strongly

affected

by

wind

(Yamaha)(Atair) (Atair)

(Thamm, 2006)

Page 19: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 19

UAV: HALE

• Flying height: some

km a.g.l., uses

kerosin

or

solar power, large coverage,  very

long

endurance

(staying

airborne

over

night!), high payload

• Very

costly

(Global Hawk)

(Luna)

(Luna)

(Luna)

(Aerovironment

Helios

/ NASA)

Page 20: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 20

UAV in use at I.P.F./TU  Wienwww.mikrokopter.de• Modular system

– Flight

control

(s/w on main

board)– controllers

for

brushless

motors

– Motors– Propellors– Receiver (feeds

flight

control)

– Transmitter– Frame– Battery

• Active

project

(fast help, etc.)• Single parts

can

be

replaced

• Software can

be

adapted

to own

needs• Supports different additional sensors• Electronics expert(ise) needed

www.mikrocontroller.com

Images not

to scale, if

not

stated

otherwise, images

from

www.mikrokopter.de

Page 21: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 21

UAV properties

• 4 rotors• 250g payload

/ 650g total mass

• Electronic stabilization

of attitude

by

gyros and accelerometers

• GPS, barometric

elevation

measurement,  magnetic

compass

• Camera mount

• Canon IXUS• Cost: €

1600

Page 22: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 22

Controlling and flying

Flying a quadro‐kopter

• neighboring

rotors

have

different rotation sense

• Additional thrust

for

one

rotor: tilts

UAV and moves

forward

• Opposing

pairs

with

different speed: yawing

Transmitter

operation

modes

(alternatives)

1.

Access to controllers

of rotors: not

used

for

multi‐copters

2.

Prescribe: Roll, Nick, Yawing

(3 orthog. axes), Thrust, Hold FC gives

corresponding

signal

to controllers

3.

Prescribe: Up, Forward, Sideways, Yawing NaviControl

gives

via FC corresponding

signal

to controllers

Page 23: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 23

Controlling and flyingTransmitter

operation

modes

(alternatives)

1.

Prescribe: Roll, Nick, Yawing

(3 orthog. axes), Thrust, Hold FC gives

corresponding

signal

to controllers

2.

Prescribe: Up, Forward, Sideways, Yawing NaviControl

gives

via FC corresponding

signal

to controllers

Degree

of Automation (switched

by

transmitter

signal)

• Prescribe

way‐points,  executed

by

NaviControl

via FC

• Manual control

Page 24: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 24

Motivation: applicationsDetailed

studies

of natural

states

and processes

• Geomorphology

• Spatial

ecology, spatial

biology, geo‐bio‐sciences, …

• Archeology

Fields relying

often

on 

• low‐tech

• experts

in the

field, therefore

detailed

analysis

• (cheap) satellite

imagery

in the

best case

• undergoing

quantification

processes

w.r.t. applied

methods

Therefore, a demand

exists

for

detailed

quantified

geo‐spatial

data.

Page 25: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 25

• Flight control (s/w on main board)• controllers for brushless motors• Motors• Propellors• Receiver (feeds flight control)• Transmitter• Frame• Battery

Assembling a UAV

frame +landing

skid

+motors +controllers +cables

to flight

control +flight

control

+rotors+GPS unit +camera

mountImage of first

flight

Page 26: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 26

First flight …

Page 27: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 27

Adaptations

• Camera mount

for

fixel

vertical

view

and less

vibrations

• Landing

rack

adaptation

• Camera– repetetive

exposures

with

constant

time interval

– no zoom, no focus

(time delay!)

Page 28: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 28

Camera

Canon IXUS 80• 8 Mpixel, ~6-18mm principle distance• Interior orientation for fixed zoom and focus found

constant within one flight mission (still a hypothesis)• Radial and tangential low order distortion improves

camera model• Short exposure time for sharp images (vibrations)

Canon Hack Development Kit• firmware „update“ of camera• manual control over focus and exposure time• allows remote exposure signals• allows repetetive exposure in constant time interval

Page 29: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 29

Second flight …

• Follows

predefined

way (parts

of the

track)

Page 30: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 30

Test in a quarry

Model from

images

alone

1. find correspondence hypotheses

(SIFT et al.)

2. evaluate

hypotheses (RANSAC et al.)

3. estimate

orientation

for entire

block of images

4. pairwise

matching

of  surfaces

5. triangulation

of point  cloud

Unresolved

• datum

(including

scale)

• no safe‐guard

against model

deformations

Page 31: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 31Agisoft Photoscan

Page 32: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 32

Direct

georeferencing

of UAV imagery

Datastreams

(3)

• Images are taken (stored on camera)

• GPS positions

are

recorded (stored

independently

on miniSD

on Navi

control)

• Acc.+Gyros

sent

from

FC to ground

laptop

(WiFi)

• Synchronization– PPS not

available

– Navi

control

data

stream

recordes

exposure

events

– Acc./Gyro

+ GPS synchronized

via logging

of identical

variable

– Camera exposure

lag constant

Images: Canon, Transcend, Mikrokopter

Page 33: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 33

Observation of Position

• GPS data

processed

onboard

by

NaviControl

• EGNOS correction

signal

exploited

by NaviControl

• European Geostationary

Navigation  Overlay

Service 

• Elevation from barometer/pressure

sensor

(initialization

on the

ground)

Page 34: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 34

Observation of angular attitude

• Gyros: observation

of angular

speed … strong drift behavior

(~ degrees/minute)

• Accelerometers: observation

of acceleration …

measure

dynamic

accelerations

gravitational

forces

• Drift behaviour

assessed

in lab experiments

g 180°

270°25°

Acceleration in nick angle: g*sin(25°)

Page 35: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 35

Gyro+Acc. lab experiments

• Different test series• Complex

test (e.g.)

shifts, rotations

(10°

each),  shift, rotations, shift, rotation

Acc.

Gyro

Page 36: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 36

Gyro behavior

• Zero level

of gyro

estimated

from

first

100 measurements

(image)• Angle integral strongly

affected

by

initial

zero

position

due

to drift. 

Therefore, zero

level

estimates

necessary

during

flight.

Accelerometer

Gyro (angular speed)

Angle (Integral)

Page 37: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 37

Modes for observing angles

• Stop

and Go for

each

exposure:  only

accelerometer

measurements

in hold position

used

for

angle measurement• Go and some

stops

– Estimate

gyro

drift from

accelerometer– Take exposures

during

flight

– Some

holds

in between

to estimate

zero

level (pull gyro

to acc)

• Optimal solution

quite

obvious, work

in progress

Page 38: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 38

Direct geo‐referencing

• Fly

over

test field

• Directly

determine

exterior orientation

by

GPS+EGNOS, 

gyros, accelerometers,  barometer

• Compute

bundle

block from

control

points (in this

case

independent spatial

resections)

Page 39: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 39

Test flight

Page 40: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 40

Coverage

of photos

for

geo‐referencing

test

Page 41: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 41

Page 42: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 42

Detail of previous

image.Note sharpness

of images. Note also image abberations.

Page 43: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 43

Direct geo‐referencing quality

• Compare

bundle

block from

control

points

to  direct

geo‐referencing

• In position:  60cm, in elevation

100cm (1 sigma!) 

shift

~ 50cm

• More

experiments

for

validation

of quality figures

missing

• Verification

with

OP missing

Page 44: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 44

Problems encountered

• 1st Mikrokopter

sensors

not

sufficiently

accurate• Crash during

landing

caused

defect

in FC

• Defect

motor

controllers

prohibited

experiments• Rotor broke

during

flight, leading

to crash

(2nd model)

• Faulty

bluetooth

module

connecting

UAV and PC• Not all measurement

written

on data

streams

• Functioning

bluetooth

module

replaced

by

WiFi

for

distance• Measurement

rates

deviate

from

prescribed

values

• GPS modules

sometimes

refused

work

mid‐air• Problems putting

new

firmware

on FC

• …

Page 45: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 45

I.P.F. Mikrokopter

GPSIMUBarometric sensor Magnetic compass

PilotCompact Camera

Notebook(Wi232 connection)

Technical data

• 4 Propeller

• Weight: 650g

• Payload: 250g

• Flight time: 15min

• Height: up to ~100m

• Range: range of sight

• Costs: ca. 1600€

Uplink: WaypointsDownlink:Sensor data

Roll and Nick compensation

Page 46: Institute of Photogrammetry and Remote Sensing … · Institute of Photogrammetry and Remote Sensing ... Experiences from assembling and operating a UAV ... Institute of Photogrammetry

Geomatics PhD school, Finland, 2011 46

Conclusions

• Direct

georeferencing

of UAV imagery

bridges across

a number

of geomatic

fields

• UAV assembly

requires

flying

and electronic expertise

• Direct

georeferencing

of UAV imagery

using on‐board

components

is

feasibile

• Practical

problems

not

to be

underestimated