OBLIQUE AERIAL IMAGERY FOR NMA SOME BEST PRACTICES

Transcription

1 OBLIQUE AERIAL IMAGERY FOR NMA SOME BEST PRACTICES F. Remondino 1, I. Toschi 1, M. Gerke 2, F. Nex 2, D. Holland 3, A. McGill 4, J. Talaya Lopez 5, A. Magarinos 5 1 3D Optical Metrology (3DOM) unit, Bruno Kessler Foundation (FBK), Trento, Italy <remondino><toschi>@fbk.eu, 2 University of Twente, Faculty of Geo-Information Science and Earth Observation (ITC), Department of Earth Observation Science, The Netherlands <m.gerke><f.nex>@utwente.nl 3 Ordnance Survey, Southampton, UK david.holland@os.uk 4 Ordnance Survey, Dublin, Ireland andy.mcgill@osi.ie 5 ICGC, Spain <julia.talaya><antonio.magarinos>@icgc.cat

2 NMCAs Research Org. 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: EuroSDR & oblique aerial imagery 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 multiplatform photogrammetry +

3 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 USGC-9 Vexcel Osprey Source: Wikipedia Zeiss twin RMK Leica DRC30

4 Current oblique aerial systems General classification of oblique digital cameras single swiping camera VisionMap

5 Current oblique aerial systems General classification of oblique digital cameras single swiping camera 2 cameras IGI Dual Zeiss twin RMK DiMAC

6 Current oblique aerial systems General classification of oblique digital cameras single swiping camera 2 cameras 3 cameras DLR-3K 3x Jena LMK 3x Fairchild K-17 Bagley 3-lens (1920)

7 Current oblique aerial systems General classification of oblique digital cameras single swiping camera 2 cameras 3 cameras 4 cameras NPO KSI Zeiss (1930) Rolleimetric AIC x4

8 Current oblique aerial systems General classification of oblique digital cameras single swiping camera 2 cameras 3 cameras 4 cameras 5 cameras Leica RCS30 Fairchild T-3A (1930 s) Microsoft/Vexcel Osprey

9 Current oblique aerial systems General classification of oblique digital cameras single swiping camera 2 cameras 3 cameras 4 cameras 5 cameras Multiple cameras NPO KSI 9-lens Fairchild Schiempflug (1904) Octoblique Midas (2015)

10 Current oblique aerial systems 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

11 Current oblique aerial systems 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)

12 Image block comparisons ADS80 coverage RCD30 coverage RCD30 Oblique (PentaPod) coverage

13 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

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15 EuroSDR & oblique aerial imagery 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

16 EuroSDR & oblique aerial imagery 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

17 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

18 Production of 3D vs 2.5D point clouds Reduced occlusions Advantages of oblique datasets 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 evidencebased decision making process In general, improve the quality of the geo-product offered by NMAs

19 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 25 sq. 7cm GSD #images flight time 60x40 conf. with large format camera < 400 < 1h 80x80 conf. with oblique camera > 6000 > 3h Tridicon (3DCom/Hexagon) suite seems to be the most effective solution to generate 3D building models out of dense point clouds

20 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, trueorthos 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

21 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.)

22 Conclusions (1/2) 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

23 Conclusions (2/2) 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 versus

24 THANK YOU! F. REMONDINO, I. TOSCHI, M. GERKE, F. NEX, D. HOLLAND, A. MCGILL, J. TALAYA LOPEZ, A. MAGARINOS