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Why Digital Cameras are Why Digital Cameras are Claimed to be Superior Claimed to be Superior to Film Cameras to Film Cameras John Trinder John Trinder University of New South University of New South Wales Wales Sydney, Sydney, Australia Australia

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Why Digital Cameras are Claimed to be Superior to Film Cameras. John Trinder University of New South Wales Sydney, Australia. Topics discussed. Statement on history of development of digital cameras Requirements for development of digital aerial cameras - PowerPoint PPT Presentation


  • Why Digital Cameras are Claimed to be Superior to Film CamerasJohn TrinderUniversity of New South WalesSydney,Australia

  • Topics discussedStatement on history of development of digital camerasRequirements for development of digital aerial camerasTwo solutions in development of digital aerial camerasPushbroom systemLeica Geosystems ADS40Multiple frame camerasIntergraph DMCVexcel UltraCamDCharacteristics of Digital Aerial ImagesReported Experiences with Digital CamerasAdvantages of digital camerasUnresolved questions

  • Development of Digital CamerasSteve Sasson (Kodak) developed the first digital camera 30 years agoBased on small CCD sensors from Fairchild Corporation with 100x100 pixels.Now 20-25 years on, digital cameras have adequate resolution and size to match the quality of film camerasSasson states that film will still be used for photography for some niche areasDigital imaging will largely replace film for almost all applications [but how much for aerial photography?]Future developments in photography are hard to predict, but almost limitless. There are more uses for images and more images being taken than ever before.

  • High Resolution Digital Aerial Cameras Digital photogrammetry has developed significantly over the past 15 yearsInclude efficient software for the production of DEMs, orthophotos and vector mapping Development of digital aerial cameras has taken time, due to demands of: Large area coverageHigh spatial resolution of the order of 400Mpixels or GSD of 10cm to 20cm High geometric accuracyEfficient management of TBytes of image data during imagingIt is expected that developments will take advantage of the characteristics of digital technologies

  • High Resolution Digital Aerial CamerasTwo solutions for development of digital aerial camera now availableThree linear arrays look forward, vertically and backwards to form three separate images as the aircraft moves over the terrain surface. Images not perspective projections System must include GPS/INSImages from smaller area arrays are stitched together to form a larger frame image, which will have similar dimensions to a frame aerial film camera Images will be perspective projectionsNo GPS/INS system required

  • Camera ConceptsDMSADS40Multi lens sensors with up to eight lenses generates patchwork framesSingle lens sensor with 10 channels generates endless pixel carpetsUltraCam

  • digital frames Digital Camera Concepts

  • Leica Geosystems ADS40

    Wehrli 3-DAS-1

    Focal length

    62.5 mm

    110mm (or 80mm)

    Pixel size (pitch)

    6.5 m

    9 m

    Panchromatic line

    2 * 12000 pixel (staggered)

    3 * 8023 pixels

    RGB and NIR line

    12000 pixels


    FoV (across track)



    Stereo angle forward to nadir



    Stereo angle forward to backward

    42 - B/H=0.77

    42 - B/H=0.77

    Stereo angle nadir to backward



    Dynamic range



    Ground sample distance

    16 cm at 3000 m altitude

    18cm at 2200m

    Swath width (3000 m Altitude)

    3.75 km

    3.75km at 2200m


  • composed of backward view linescomposed of nadir view linescomposed of forward view linesBackward scene Nadir sceneForward sceneBackwardNadirForwardThree-line Pushbroom Scanner

  • Push-broom sensorsThe geometry of the complete image is not a perspective projection. Hence, special software is required.GPS/IMU system is essential to determine the camera exterior orientation (positions and attitude) during flight extra cost Linear arrays are less subject to loss of pixels If bad pixels do occur, fewer pixels available to interpolate lost dataLinear arrays are claimed to have larger dynamic range Linear arrays in principle are more suited to smaller scale imaging because of motion of the aircraft. Linear array systems have recently demonstrated GSD of 5cmMost linear array systems enable the acquisition of only 3 images per point along-track, but multiple imaging is possible across-track

  • ADS40 unrectified

  • ADS40 rectified

  • Multiple Frame CamerasIntergraph (formerly Z/I Imaging) DMCVexcel UltraCamSimultaneous acquisition of 4 frames - 7kx4kPanchromatic - Syntopic data acquisition of 9 frames with camera at identical positionsPixel size (pitch)12 m9 mField of View69.3 cross track x 42 along track B/H=0.30 for 60% olapB/H=0.60 for 20% olap55 cross track x 37 along track B/H=0.27 for 60% olapB/H=0.50 for 20% olapPanchromatic imagesLensf 120mm/f4f= 100mm/f5.6Final output7,680 x 13,824 pixels7,500 (flight direction) x11,500 pixels

  • Multi-spectral imagesLensf 25mmf-28mm/f4ColoursB, G, R, IR, alternate IRR, G, B, IRShutters and f-stop1/50 1/300s, f4-f221/60 - 1/500s, fRadiometric resolution12-bitBetter than 12-bitGround sampling distance5cm @ 500m3cm @ 300mFMCyesyes

    Multiple Frame CamerasIntergraph (formerly Z/I Imaging) DMCVexcel UltraCam

  • Multiple Frame CamerasThe images have the same perspective geometry as normal aerial imagesNo GPS/IMU system is required There are many more neighbouring pixels from which to interpolate new pixel values for the erroneous dataArray imaging enables aerial triangulation of multiple redundant frame images leading to high geometric accuracyIf a high quality GPS/IMU system is installed for direct orientation, aerial triangulation may be avoided

  • image mosaicingapply camera calibration parametersapply platform calibrationImage Processing

  • Combination of Sub-images to Create Single Virtual Image3D-combination of sub-images bundle adjustment of one sub-image to the other based on tie pointsGeneration of virtual image including geometric corrections virtually image distortion freevirtual imagesub-image

  • Test flight Germany Feb 2002Flying Height = 150mGSD = 1.5cmVelocity ~ 140 kts (70 m/sec)Exposure time = 1/100 secFMC Shift ~ 50 pixelsSample Image

  • Sample Image

  • Pan-SharpeningPanchromatic Original Color Pan-sharpened Color

  • Conclusions from Accuracy TestsGeometric accuracy better than analog cameraLess favorable B/H ratio is compensatedExcellent height accuracyPotential to fly at higher altitudes with fewer strips

  • Multiple area arrays -Vexcel UltraCam

  • Characteristics of Digital Aerial ImagesThe cross-track coverage for pushbroom cameras is typical about 46 or lessArray cameras cross-track coverage is generally larger Coverage does not approach that of standard film cameras. Along-track coverage of area array cameras varies from 42 for the Intergraph DMC to 37 for Vexcel UltraCamD B/H is about 0.7 B/H for push-broom cameras, 0.3 for are array camerasWith 80% overlap B/H is 0.6 for the DMC and 0.5 for the UltraCamD. Improved quality of the digital images results in better quality image matchingClaimed to negate the impact of the smaller B/H.

  • Characteristics of Digital Aerial ImagesPixels sizes can vary from 5cm to 1mThe new generation digital aerial cameras will lead to a paradigm shift in photogrammetry. It should not be necessary to limit the number of photographs acquired on the basis of manual handling. Highly redundant photography with much large percentage overlaps Should result in significantly more reliable aerial triangulation of the images, Image processing for elevation determination based on image matching from multiple images, True or near-true orthophotos will be acquired, in which the layover of buildings will be largely eliminated.

  • Reported Experiences with Digital CamerasIn Japan ADS40 has been shown to have the potential for 1:2,500 scale mapping Digital images will be applied to 1:1,000 mapping. Map production is faster and more economical than with traditional photogrammetry. Operations for mapping urban areas with very narrow streets with a Z/I Imaging DMS cost less than half that of film-based camera missions. More than 12,000 images in 40 projects were collected in a period of 6 months. Digital cameras can generate inexpensive true orthophotos, based on 80% overlaps along and across the strips. The increased overlap allowed for the extraction of accurate DEMs for ground features as well as vertical structures.

  • Reported Experiences with Digital CamerasIn USAShortened production cycle and more accurate, realistic aerial images for tournament maps ADS40 imagery acquired for orthophoto production over approximately 1 million square km - 10 Terrabytes of data in 3 month periodIn BelgiumNo significant difficulties in introducing the UltraCamD into operations and adapting to new system in flight planning.More than 5000 images taken in three days and just a few days later the photos passed through quality assurance Quoted accuracies of processing this data have been as high as 2-3 m on the imageImage matching of digital images with larger overlaps more reliable than for standard aerial photography with 60% overlap.

  • Conclusions on development of digital camerasStated requirements:Large area coverageHigh spatial resolution of the order of 400Mpixels or GSD of 10cm to 20cm High geometric accuracyEfficient management of TBytes of image data during imagingAchievements:Area of coverage is less than standard film cameras, but compensated by increasing overlaps Eliminated degrading effects of film and improved dynamic range resolutions less than 10cm achievable

  • Conclusions on benefits of digital camerasAchievements (cont):Despite lower B/H, achievable geometric accuracies are as good as or better, than for film aerial photogrammetry Increased overlaps possible at little extra costData management of large volume of data has been overcomeOther BenefitsNear real orthophotos possibleMore data acquisition per day and throughout the year, especially in higher latitudesProcessing of images can be done as soon as the aircraft lands, leading to more rapid throughputNew markets should be available for high resolution orthophotos and vector mappingNew opportunities in remote sensing with high resolution multi-spectral images

  • Unresolved Digital Camera QuestionsLong term archival of digital dataImpact of calibration of multiple lensesHow robust and durable are the cameras?What are the implications for calibration of cameras comprising up to 9 separate lenses?What is the life span of digital cameras?How quickly will they provide a return on investment?

    Airborne Imaging Scenes:The airborne digital sensor works like a push-broom scanner, recording continuously as the aircraft moves forward. When the recorded lines are put together they form a scene. Since three lines are recorded simultaneously three types of scenes are being formed: the forward scene composed exclusively of forward view lines the nadir scene composed exclusively of nadir view lines the backward scene composed exclusively of backward view lines