Why Digital Cameras are Claimed to be Superior to Film Cameras

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

2. Topics discussed • Statement on history of development of digital cameras • Requirements for development of digital aerial cameras • Two solutions in development of digital aerial cameras • Pushbroom system • Leica Geosystems ADS40 • Multiple frame cameras • Intergraph DMC • Vexcel UltraCamD • Characteristics of Digital Aerial Images • Reported Experiences with Digital Cameras • Advantages of digital cameras • Unresolved questions

3. Development of Digital Cameras • Steve Sasson (Kodak) developed the first digital camera 30 years ago • Based 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 cameras • Sasson states that film will still be used for photography for some niche areas • Digital 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.

4. High Resolution Digital Aerial Cameras • Digital photogrammetry has developed significantly over the past 15 years • Include 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 coverage • High spatial resolution – of the order of 400Mpixels or GSD of 10cm to 20cm • High geometric accuracy • Efficient management of TBytes of image data during imaging • It is expected that developments will take advantage of the characteristics of digital technologies

5. High Resolution Digital Aerial Cameras • Two solutions for development of digital aerial camera now available • Three 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/INS • Images 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 projections • No GPS/INS system required

6. Camera Concepts ADS40 Single lens sensor with 10 channels generates endless pixel carpets DMS UltraCam Multi lens sensors with up to eight lenses generates patchwork frames

7. pixel carpets Digital Camera Concepts digital frames

9. DATA ACQUISITION BY LEICA GEOSYSTEMS ADS40

10. Three-line Pushbroom Scanner Backward scene Nadir scene Forward scene composed of backward view lines composed of nadir view lines composed of forward view lines Backward Nadir Forward

11. Push-broom sensors • The 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 data • Linear 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 5cm • Most linear array systems enable the acquisition of only 3 images per point along-track, but multiple imaging is possible across-track

12. ADS40 unrectified

13. ADS40 rectified

16. Multiple Frame Cameras • The images have the same perspective geometry as normal aerial images • No GPS/IMU system is required • There are many more neighbouring pixels from which to interpolate new pixel values for the erroneous data • Array imaging enables aerial triangulation of multiple redundant frame images leading to high geometric accuracy • If a high quality GPS/IMU system is installed for direct orientation, aerial triangulation may be avoided

18. 4 overlapping images • tie point check • robust adjustment • projection to virtual perspective • fusion with colour composite tie point area Image Processing • image mosaicing • apply camera calibration parameters • apply platform calibration

19. Institut für Photogrammetrie und GeoInformation Universität Hannover 3D-combination of sub-images bundle adjustment of one sub-image to the other based on tie points Generation of virtual image including geometric corrections  virtually image distortion free Combination of Sub-images to Create Single Virtual Image sub-image virtual image

20. Sample Image Test flight Germany Feb 2002 Flying Height = 150m GSD = 1.5cm Velocity ~ 140 kts (70 m/sec) Exposure time = 1/100 sec FMC Shift ~ 50 pixels

21. Checkered Tablecloth Grid Size ~ 2 inches Sample Image

22. Pan-Sharpening Panchromatic Original Color Pan-sharpened Color

23. Conclusions from Accuracy Tests • Geometric accuracy better than analog camera • Less favorable B/H ratio is compensated • Excellent height accuracy • Potential to fly at higher altitudes with fewer strips

24. Multiple area arrays - Vexcel UltraCam

36. Characteristics of Digital Aerial Images • The cross-track coverage for pushbroom cameras is typical about 46º or less • Array 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 42º for the Intergraph DMC to 37º for Vexcel UltraCamD • B/H is about 0.7 B/H for push-broom cameras, 0.3 for are array cameras • With 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 matching • Claimed to negate the impact of the smaller B/H.

37. Characteristics of Digital Aerial Images • Pixels sizes can vary from 5cm to 1m • The 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.

38. Reported Experiences with Digital Cameras • In 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.

39. Reported Experiences with Digital Cameras • In USA • Shortened 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 period • In Belgium • No 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 µm on the image • Image matching of digital images with larger overlaps more reliable than for standard aerial photography with 60% overlap.

40. Conclusions on development of digital cameras • Stated requirements: • Large area coverage • High spatial resolution – of the order of 400Mpixels or GSD of 10cm to 20cm • High geometric accuracy • Efficient management of TBytes of image data during imaging • Achievements: • 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

41. Conclusions on benefits of digital cameras • Achievements (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 cost • Data management of large volume of data has been overcome • Other Benefits • Near ‘real’ orthophotos possible • More data acquisition per day and throughout the year, especially in higher latitudes • Processing of images can be done as soon as the aircraft lands, leading to more rapid throughput • New markets should be available for high resolution orthophotos and vector mapping • New opportunities in remote sensing with high resolution multi-spectral images

42. Unresolved Digital Camera Questions • Long term archival of digital data • Impact of calibration of multiple lenses • How 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?