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  1. 1. Systematic Oblique Aerial Photography Using Multiple Digital Cameras by Prof. Gordon Petrie(Univ. of Glasgow ) VIII International Scientific & Technical Conference From Imagery to Map: Digital Photogrammetric Technologies September 15-18, 2008 Porec, Croatia
  2. 2. Oblique Photography - Introduction
    • I - Multiple Oblique Photographs
    • (a) Currently much interest in oblique photography - partly triggered by the high-profile activities ofPictometryand its licensees and competitors.
    • (b) This has involved the systematic coverage of urban areasusing multiple oblique aerial cameras. Huge numbers of photographs are being generated Pictometry operate 70 aircraft in the U.S.A.; Blom 13 aircraft in Europe ; and so on.
    • (c) In its report on the ISPRS 2008 Congress ,our hosts, Racurs,wrote
    • (i) There is a strong movement towards combining traditionalnadir imageswithoblique imagesacquired at high angles to build3D modelsof cities with the texture of building walls taken from the oblique photos.
    • (ii) For non-specialists in theemergency services(military, police, fire, ambulance), the combination of oblique and nadir images improves theirinterpretation while special software allowssimple measurementson the oblique photos.
  3. 3.
    • II - Multiple Oblique Cameras
    • (a) Lohman (Univ. of Hannover) speaking in more general terms about technical developments, talks of are-birthof multiple oblique camera systems alluding to their extensive prior use during the period 1920 -1945 for mapping & reconnaissance purposes.
    • (b) Part of the current interest in multiple oblique camera configurations stems from the limitations in the size of current CCD & CMOS area arrays for digital cameras hence the use ofmultiple oblique camerasby a number of system suppliers toincrease the ground areathat can be covered from a single exposure station.
    • (c)Besides the increase in the coverage area of rectangular or square format digital frame photos, there is long-standing requirement on the part of military air forces to obtain the widest possiblecross-track angular coverageusingfans of oblique camerasfor reconnaissance purposes.
    Oblique Photography - Introduction
  4. 4. Oblique Photography - Introduction
    • III - Surveillance from Unmanned Airborne Platforms
    • (a )Apart from the multi-photo & multi-camera aspects of oblique aerial photography, the oblique imaging configuration is also of increasing importance for bothsurveillanceand forvisualizationpurposes with the acquisition of bothsingleandmultipledigital images from both manned and unmanned platforms often fromlow altitudes .
    • (b)There are many new developments in oblique aerial photography using digital cameras operated throughradio linkson numerous types ofunmanned airborne platformsfromlow altitudes:
    • (i) robotic mini-helicopters ;
    • (ii) powered mini-airships ;
    • (iii) powered paragliders ;
    • (iv) tethered blimps ; and
    • (v) telescopic masts
  5. 5. Oblique Photography (Manned) (a)Area of great activity in some countries e.g. inU.K.,more than60 companiesengaged in this field. (b)Oblique photos used extensively forvisualizationby estate agents & property developers; formonitoring progresson projects (for payments) by civil engineers and builders. (c)Oblique frame photos arecommissionedspecifically for a particular site or property or area on contract not for stock. (d)MostlyCessna 172aircraft are used widely available; very cheap to operate -200per hour. (e)Some limited use ofhelicopters , but very high cost to operate 800per hour.
  6. 6. Oblique Photography (Unmanned)
    • (a)The acquisition of oblique aerial photography byunmanned meansis an area of strong development.
    • (b)The use ofradio-controlled mini-helicoptersis now becoming common circa10 commercial companiesin this field in U.K..
    • (i)Mini-helicopters are 1.5 to 2m long & fitted with an anti-vibration camera mount.
    • (c) Powered mini-airshipshave also come into more limited use.
  7. 7. Oblique Photography (Unmanned) (d)The use oftethered (unpowered) blimpsis also very widespread more than10 companiesoperating in the U.K. (e)Most widespread of all is the use oftelescopic masts in U.K.,55 companiesoperate in this market. (f)Bothfilm & digital frame camerasare used to acquire the required oblique aerial photography.
  8. 8. Oblique Photography (Unmanned) Use of digital cameras from unmanned platforms by theSkycell company.
  9. 9. Single Cameras Multiple Obliques Stepping frame camera- A sequence of oblique photos is exposedcross-trackat a very high speed to provide avery wide angular coverageof the ground. VisionMap (Israel) Twin cameras side-by-side in a cross-track scan.
  10. 10. Two Oblique Cameras
    • (a)Twin oblique film cameras have been used extensively in the past to provideincreased coverageeithercross-trackoralong-track .
    • (b)When two long focal length, narrow angle cameras are used, these are calledsplit-verticalsF21 -F22 .
    • (c)As well as pairs of cameras, there was extensive use offansof four ( F41-F44 ) or six ( F61 - F66 ) cameras to give still greater cross-track coverage.
    Twin Zeiss RMK Cameras
  11. 11. Two Oblique Cameras
    • (a)There is increasing use of twin obliquedigital frame camerasto provide increased cross-track coverage.
    • (b) DiMAC Systems(Belgium) offers itsDiMAC Widetwin-camera unit.
    • (i)Two 7.2 x 5.4 k ( 39 Mpix ) images giving a totalcoverageof10.5 x 7.2 k pixels .
    • (ii)Eitherf = 55or80or120 mm lenses
    • (iii)Cylindricalcarbon-fibrebox.
    • (iv) DiMergesoftware to rectify & merge the two images.
  12. 12. Two Oblique Cameras (a) IGI(Germany) offers itsDual-DigiCAMsystem. (b)Comprises twin digital cameras (Hasselblad-based) with39 Mpixdigital backs. (c)One exposure = 2 photos. (d)Rectification & stitching. (e)Again wide cross-track coverage 10kor13kpixels. Final rectified & stitched image with wide cross-track coverage Flight diagram for three strips of dual oblique images
  13. 13. Two Oblique Cameras
    • Rolleimetric(Germany) also offers itsAIC x2twin digital camera unit, with a similar specification to that of DiMAC Wide.
    Final stitched (rectified) image with wide cross-track coverage
  14. 14. Three Camera Systems
    • (a)Extensive use of three film frame camera systems with1 verticaland2 oblique cameras- was made during the1930sand1940s .
    • (b)Some were purpose-built units; however most used 3 separate film cameras.
    • (c)During World War-II, much use was made of so-calledTri-Metrogon photographyfor small-scale mapping & charting by the U.S.A. ThreeFairchild K-17film cameras 1 vertical + 2 oblique.
    • (d)This arrangement has continued to be used extensively bymilitary air forcesworld-wide.
    3 x FairchildK-17 cameras 3 x Jena LMK cameras
  15. 15. Three Lens Cameras
    • (a)Purpose-builtBagley3-lens filmcamera from the late 1920s.
    (b)TheZeiss KS-153 Trilens 80film camera is much used by West European air forces.
  16. 16. Three Camera System
    • (a) TheGerman Space Agency (DLR)has developed a similar system DLR-3k - with 3 Canon EOS digital frame cameras - for use in traffic studies.
    • (b)Again a widecross-trackcoverage of the ground.
  17. 17. Four Camera Systems
    • (a)Russian four-camera systems fromNPO KSI
    • (b)Use ofmultiple CCD arraysin conjunction withmultiple lensesto give increased cross-track coverage.
  18. 18. Four Camera Systems Again the arrangement of theZeissfour-coupled oblique film cameras from the 1930s is being replicated in the newRolleimetric AIC x4digital camera system.Final rectified & stitched orthophoto Four separate (tilted) photos
  19. 19. Four Camera Systems
    • Intergraph DMC
    • (a) 4 medium-formatoblique frame cameras with the tilted images rectified and merged to form 108 Mpixpanimages.
    • (b) 4 small-format vertical cameras forcolour , each 2k x 3k = 6 Mpix covering a different spectral band
    FDS High Density Disks DMC with Solid State Disk
  20. 20. Four Camera Systems
    • Intergraph DMC
    • (a)Originally 4oblique(pan) + 3vertical(multi-spectral) images.
    • (b)Final production camera gives 4oblique(pan) + 4vertical(multi-spectral) images.
    Plan View Cross-section
  21. 21. Four Camera Systems Intergraph DMC (a)Each of the 4 medium-format oblique pan images isrectifiedand they are thenstitchedtogether using tie points in the overlap areas. (b)The final virtual image is then colourized using the data from the four small-format multi-spectral cameras
  22. 22. Five Lens Cameras
    • (a)Five-lensfilm camerasare still in extensive use e.g. in GermanTornadoreconnaissance aircraft.
    • (b)TheZeiss KS-153camera in itsPentalens 53version uses 5 lenses in parallel - with special prisms used to obtain each of the four oblique photos.
  23. 23. Five Camera Systems (a)During the 1930s, extensive use of theFairchild T-3A5-lens film camera systems in the U.S.A. (b)Each comprisedone vertical & four oblique camerasin a single housing with 5 separate film magazines.(c)30 T-3A systems were built. (d)Lenswasf = 150mm ; each of the five photos was13.5 x 15 cmin size (e)Produced a Maltese Cross coverage of the ground. (f)The photography was used extensively byUSCEandUSGSfor mapping using both graphical radial triangulation and stereo-plotting instruments.
  24. 24. Five Camera Systems
    • (a) The same configuration of one vertical and four oblique cameras has been adopted for thedigital camera systemsnow being used to acquire systematic coverage of digital oblique photos.
    • (b) Largest and best known company isPictometry which has licensed its technology to(i) MDA(Canada)
    • (ii) Blom Aerofilms(Europe)
    • (iii) AAMHatch(Australia/S.E. Asia)
    • (iv) AOC(South Africa)
    • (v) KKC(Japan); etc.
    • (c) Several smaller independent companies Geospan(U.S.A.);COWI(Denmark);Ofek(Israel);GetMapping(U.K.);Mapaid(Norway), etc. also compete in this specialized market.
    • (d) Great deal oflegal actionis currently in progress overpatentsissued by the U.S. Patent Office.
  25. 25. Five Camera Systems
    • (a) TrackAir(Oldenzaal, Netherlands) is the main independent supplier of these five camera systems
    • (b) ItsMIDASsystem can be fitted to any aircraft with a standard camera port or to a smaller hole.
    • (c) The five cameras are all standardCanon EOS-1 DS Mk-II(16.7 MPix) orMk-III(21 MPix) models.
    • (d) 5 x 16.7 Mpix =83.5 Mpix ;5 x 21 MPix =105 Mpixper exposure.
    • (e)Camera Lenses
    • (i) Nadir- f = 23.8 mm; 72 x 52
    • (ii) Oblique- f = 51 mm; 39 x 26 with 45 angle to vertical.
    • (f) ApplanixPOS/AV is used as the GPS/IMU system
    Standard Port External Fairing Floor Floor
  26. 26. Five Camera Systems
    • (a)The use of acylindrical external fairingis to protect the five camera unit when it is attached to the underside of the aircraft.
    • (b)The complete unit is shown being attached to aCessna 172aircraft
    Installation in aCessna 404aircraft (Belgium) without a fairing TrackAir MIDAS MIDAS Data Computer & Controller
  27. 27. Five Camera System
    • Image Processing Software
    • (a) A large Israeli software house-Idan Computerhas been offering its Oblivision software package for many years for the rectification of the oblique images and the formation of orthophotos.
    • (b)Also allowsimage analysisandsimple measurementson the photos.
    • (c)Integrates the images withDEMs.
    • (d)Mainly used by military and security agencies in Israel & the U.S.A.
    • (e)Sold byIntelepixin the U.S.A.
    Al-Aqsa Mosque, Jerusalem
  28. 28. Five Camera System
    • Image Processing Software
    • (a) MultiVision is another similar software package from Israel produced by theOfekAerial Photography & Mapping company.
    • (b)Orientation and rectification carried out using either(i) ground control points ;(ii) points on maps ; or(iii) airborne GPS/IMU data .
    • (c)Continuousgeo-referencing(in plan position coordinates) and the possibility to measuredistances, areas, elevations, facades, etc.
  29. 29. Five Camera System
  30. 30. Five Camera System (a) COWI(Denmark) operates two of theMIDAS five-camerasystems for the acquisition of systematic oblique photography. (b)The company formerly usedMultiVision ; now it uses its own software.
  31. 31. Five Camera Systems
    • (a) AlthoughPictometryis the leading player in this field, they will not release any details of their imaging technology.
    • (b)However it is thought (by outside observers) that thecamerasused in their systems are supplied by theIMPERX company based in Florida.
    • (c)IMPERX is a large specialist American supplier ofhigh-resolution cameras & frame grabbersfor military UAVs; for machine vision; and for medical applications.
    • (d)IMPERX offers11 or 16 Mpixcameras.
    • (e)Pictometry has constructed its owncalibration cagefor these cameras. A copy has been supplied toUSGSfor use in its new digital camera calibration facility at its EROS Data Center.
  32. 32. Five Camera System
      • (a)Like its competitors, the Pictometry five-camera system is used to carry out thesystematic coverageof large areas of ground using parallel flight lines - instead of photographing specific sites.
    • (b)Required area is divided into communities of 1 sq. mile; each is photographed from 4,000 ft. (1,200 m) with 1.5ft. (0.45 m) ground resolution.
    • (c)Each community is sub-divided into neighbourhoods and then re-photographed from 2,000 ft. (600 m) with 0.5ft. (0.15 m) ground resolution.
    • (d) Over 70 camera systems in use.Huge numbersof photos are produced 350,000 photos to cover Los Angeles; 500,000 to cover Massachusetts.
    • (e)Much used bylaw enforcement agencies+emergency services .
    • (f)Unlike the other systems, the Pictometry system involves the use oflicensed imagery the image libraries remain the property of Pictometry.
    • (g)The licensed imagery is bundled with PictometrysElectronic Field Studysoftware allowing the viewing of the multiple images and provision of tools for location and for the measurement of distance, area, elevation, etc.
  33. 33. Five Camera System CommunityOrthoImageCommunityObliqueImage
  34. 34. Five Camera System NeighbourhoodObliqueImage
  35. 35. Five Camera System Pictometry Applications (a)In the U.S.A., the biggest use of Pictometry imagery appears to be byhomeland security(police) agencies &emergency (fire, ambulance) services. (b)Images are available on laptops or are sent byradio .
  36. 36. Five Camera System Pictometry images are much used also on theMicrosoft Virtual Earthmapping & imaging platform
  37. 37. Five Camera System
  38. 38. Five Photo System
    • (a)In the U.K., a system using asingle camerato take four oblique photos in very rapid succession is being operated by theGetMapping company.
    • (b)Thefifth (vertical) photois already provided from the companys existing coverage of the U.K.
    • (c) ThisAzicamsystem has been built by theGeotechnologies unit of Bath Spa University.
  39. 39. Multi-Lens Film Cameras (a)The famous8-lenscamera ofSchiempflugfrom1904used to take aerial photos from blimps. (b)TheBarr & Stroud 7-lenscamera designed byE.H. Thompson ; built in the 1930s.
  40. 40. Multi-Lens Film Cameras (a)Another well-known example is the9-lenscamera ofAschenbrennerfrom1926 ; a later version was built forPhotogrammetrie GmbH . (b)This camera was used to acquire the first aerial photography used for the mapping of the Russian Arctic islands from theGraf Zeppelinairship in1931 .
  41. 41. Multi-Lens Film Cameras Another well-known9-lenscamera to a similar design byReadingof the U.S.Coast & Geodetic Survey(now part of NOAA) - that was built byFairchild.
  42. 42. Six Camera System (a)Severalsix-coupled camerashave come into operation recently. (b)From theU.S.A.have come theITT/Geospatial Systemssix-pack with real-time transmission of the images (66 Mpix) to the ground station forpersistent surveillance . (c)Follow-on scaleable systems with amuch larger number of oblique camerasare being built that will produce 176 Mpix and 584 Mpix images respectively.
  43. 43. Six & Eight Lens Digital Camera Systems
    • The RussianNPO KSIcompany has produced multiple oblique digital cameras with(i) six lensesand18 CCD area arrays ; and(ii) eight lensesand32 CCD area arraysrespectively. These give very wide cross-track coverages of 27,000 and 49,000 pixels respectively.
  44. 44. Multiple Lens Digital Oblique Cameras Summary & Conclusions
    • (a)Once again - as in the period 1920 to 1940 -multi-lensandmulti-camera imaging systems acquiring digitaloblique aerial photosare part of the current photogrammetric imaging and mapping scene.
    • (b)At the present time,many more digital oblique imaging systemsare being designed and built:
    • (i)on themilitaryside, the use of Scaleable Systems to provide large area coverage for Persistent Surveillance purposes ; and widecross-track coverageforreconnaissance purposes .
    • (ii)on thecivilianside, oblique cameras for the provision oflarger-format imageryformapping purposes ; and for the acquisition ofhigh-angle oblique imageryspecifically forvisualization purposes .
    • (c) Photogrammetric software systemswill have to cope with these current developments on the airborne data acquisition side usingmultiple oblique digital cameras .