OBLIQUE AERIAL IMAGERY FOR NMA SOME BEST...

Fabio Remondino - OBLIQUE AERIAL IMAGERY for NMA

F. Remondino1, I. Toschi1, M. Gerke2, F. Nex2, D. Holland3, A. McGill4,

J. Talaya Lopez5, A. Magarinos5

1 3D Optical Metrology (3DOM) unit, Bruno Kessler Foundation (FBK), Trento, Italy

Email: <remondino><toschi>@fbk.eu, http://3dom.fbk.eu

2 University of Twente, Faculty of Geo-Information Science and Earth Observation (ITC),

Department of Earth Observation Science, The Netherlands

Email: <m.gerke><f.nex>@utwente.nl

3 Ordnance Survey, Southampton, UK – Email: [email protected]

4 Ordnance Survey, Dublin, Ireland – Email: [email protected]

5 ICGC, Spain – Email: <julia.talaya><antonio.magarinos>@icgc.cat

OBLIQUE AERIAL IMAGERY FOR NMA

– SOME BEST PRACTICES –


EuroSDR & oblique aerial imagery

EuroSDR is an organization composed of

European NMCAs/NMAs and research

organizations of most EU member states

EuroSDR is following the development of oblique

aerial cameras since 2013, when a research

activity was created to:

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Researc

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continuously update its members on the developments in this technology

explore more deeply the potential of oblique imagery

investigate performances of hardware and software solutions

provide practical and cost-effective methodologies for mapping agencies

underline substantial technical and operational benefits

provide clear statements and best practices

Oblique research activity of EuroSDR is couple to the ISPRS Scientific

Initiative on “Multiplatform Photogrammetry” – see presentation on Saturday

16/Jul/2016: 10:30am-12:00pm, room Club B

Gerke, M., Nex, F., Remondino, F., Jacobsen, K., Kremer, J., Karel, W., 2016: Orientation of

oblique airborne image sets - Experiences from the ISPRS/EuroSDR benchmark on multi-

platform photogrammetry


Oblique imagery and cameras

First recorded aerial photo in the US (1860) by J.W. Black and S. King in

Boston (USA) was an oblique shot from a balloon

In the two World Wars, oblique were used for inspection & reconnaissance

In the “analogue times” too expensive technology

Almost 10 years ago: Pictometry system

Nowadays different systems available

A “returned” technology / system

Source: Wikipedia

USGC-9

Zeiss twin RMK Leica DRC30

Vexcel Osprey’


General classification of oblique digital cameras

Current oblique aerial systems

single swiping camera

VisionMap

../../../../Users/aa/Videos/VisionMap's Motion Compensation Technology.mp4





2 cameras

Zeiss twin RMK

IGI Dual

DiMAC





2 cameras

3 cameras

3x Fairchild K-17 Bagley 3-lens (1920)

3x Jena LMKDLR-3K




Zeiss (1930)

NPO KSI


2 cameras

3 cameras

4 cameras

Rolleimetric AIC x4




Fairchild T-3A (1930’s)

Leica RCS30


2 cameras

3 cameras

4 cameras

5 cameras

Microsoft/Vexcel Osprey




Schiempflug (1904)

NPO KSI single swiping camera

2 cameras

3 cameras

4 cameras

5 cameras

Multiple cameras

9-lens Fairchild Octoblique Midas (2015)



Fan (static or sweeping) vs Maltese Cross configuration

- IGI Dual Cam

- A3 Visionmap- Track‘Air MIDAS

- IGI Penta DigiCam

- Hexagon/Leica RCD30

- Pictometry / BlomOblique

- Microsoft/Vexcel Osprey





Maltese Cross configuration

One vertically pointing camera + 4 oblique cameras

pointing to the four cardinal directions

Modular (i.e. varying angles) vs fixed

Small vs medium vs large format camera sensors

RGB + NIR (in the nadir)

Wide vs narrow angle lens

Larger image block (more strips, more overlap, more

redundancy)



Image block comparisons

ADS80

coverage

RCD30

coverage

RCD30 Oblique

(PentaPod)

coverage


Oblique aerial systems - Open research issues

handling of occlusions, scale and radiometric changes

correct and fast identification of homologues points, in particular across

viewing directions

automatic AT with well distributed tie points

direct geo-referencing

use of relative orientation among the oblique views

processing time

redundancy / overlap exploitation

fusion of point clouds coming from different viewing directions (and with

different accuracy & resolution)

automation in interpretation, especially for complex architectures

etc.

→ Most of these issues were tackled

within the EuroSDR research activity

on oblique aerial cameras



Main participant of the EuroSDR “oblique research activity”:

FBK Trento, Italy

ITC / Twente University, The Netherlands

Ordnance Survey (OS) UK

Ordnance Survey (OS) Ireland

Institut Cartogràfic i Geològic de Catalunya (ICGC), Spain



Performances of existing hardware and software (benchmark)

Needs for using oblique flights / images wrt standard nadir

acquisitions

Advantages of oblique datasets

Lesson learnt from internal experiences

Limitations of the oblique pipeline wrt the standard nadir solution

Visions


Needs for using oblique flights

Nadir flights for:

update of topographic maps,

production of orthophotos,

creation of national-wide DSMs/DTMs,

generation of Building Height Attribute, etc.

Oblique flight for:

3D object extraction and modeling,

improve realistic appearance of (3D) geo-products,

improve urban mapping,

reduce occlusions,

improve reliability and redundancy


Advantages of oblique datasets

Production of 3D vs 2.5D point clouds

Reduced occlusions

Derivation of 3D topographic layers / info directly from 3D point clouds

(no need for stereo restitutions)

Measurements on building façades and, generally, in narrow streets

Better modeling of man-made and complex objects (sheers,

overhangs, canopies, underpasses, etc.)

Territory identification and interpretation for more efficient evidence-

based decision making process

In general, improve the quality of the geo-product offered by NMAs


Lesson learnt from internal experiences

Better performance with 80x80 overlap configuration and GSD in the

order of 6-7cm (Maltese cross configuration / cameras)

Reducing overlap to the usual 60x60 or 60x40 produce noisier

correlation and higher occlusions → need for larger overlap, so

blocks!

Parallelization (no Cloud) is very mandatory to speed up processing

(an oblique block is ca 10 times larger than a nadir block)

Covering large areas requires high amount of flight hours so

illumination conditions should be carefully considered

Tridicon (3DCom/Hexagon) suite seems to be the most effective

solution to generate 3D building models out of dense point clouds

25 sq. km @ 7cm GSD #images flight time

60x40 conf. with large format camera < 400 < 1h

80x80 conf. with oblique camera > 6000 > 3h


Limitations

Medium format cameras (with Bayer filter) have an apparent

resolution smaller than the nominal flight GSD. Using synthetic

targets an effective resolutions of 1.98xGSD (R), 1.32xGSD (G) and

2.21xGSD (B) were obtained

Current off-the-shelf workflows for image processing, aerial

triangulation (AT), dense point cloud and 3D data generation have

important room for improvement

Often manual intervention for subdividing blocks and facilitate AT

procedures is requested

Although DIM produce more dense and complete point clouds, true-

orthos suffer of DIM results, thus DTM still primary source

Image block size and management

Tools for 3D building generation from dense point clouds normally do

not consider points of the façades


Visions

Soon oblique will be a common source for 3D urban areas and to

create high resolution 3D datasets

New algorithms and solutions will improve data processing

performances and results

Oblique imagery will facilitate the complete automatization of

LOD2-3 building extraction based on multi-view algorithms

Oblique will increase user’s expectation wrt current and standard

products (e.g. true-ortho, quality 3D textured building models, etc.)


Oblique camera systems are definitely back and a promising

solution for mapping purposes

Different systems available, new coming out soon on the market

Oblique airborne images will probably become a standard

complementary to traditional large format nadir images

Oblique will not replace traditional nadir acquisitions (urban areas)

Many possible applications: map update, 3D city modeling,

inspection, interpretation, footprint identification, 3D cadastre, real

estate, etc.

NMAs are slowly thinking to adjust their production pipeline to cope

with oblique datasets

Oblique requires a new approach in the photogrammetric and

production pipeline

Data acquisition (flight plan) + Data processing (convergent, huge point clouds,

etc.) + 3D restitution / Automated interpretation

Conclusions (1/2)


Additional costs of oblique flights (especially additional flight lines)

might be compensated by additional outcomes and benefits

Benefit offered by oblique imagery are not yet compelling enough to

result in a commitment to operational use of oblique flights

The images volume in a project increases dramatically affecting image

management, AT, dense matching, storage and archive operations

Very dense, accurate and detailed point clouds but then?

New solutions to derive structured information out of unstructured point clouds

Large polygonal models (e.g. GoogleEarth) are not useful for NMAs if not only

for visualization

Conclusions (2/2)

versus


THANK YOU!

F. REMONDINO, I. TOSCHI, M. GERKE, F. NEX, D. HOLLAND,

A. MCGILL, J. TALAYA LOPEZ, A. MAGARINOS

OBLIQUE AERIAL IMAGERY FOR NMA SOME BEST...

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