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Departement Ingenieur

Departement Ingenieur. Industrieel Bouwkunde. afdeling. S Y L L A B U S P H O T O G R A M M E T R Y MODULE 4: INTRODUCTION TO THE USE OF SCALEDRECTIFIED PHOTOGRAPHY AND PANORAMIC PHOTOGRAPHY. Projection. Projection. Vertical vanishing point (at infinity).

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Departement Ingenieur

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  1. Departement Ingenieur Industrieel Bouwkunde afdeling S Y L L A B U S P H O T O G R A M M E T R Y MODULE 4: INTRODUCTION TO THE USE OF SCALEDRECTIFIED PHOTOGRAPHY AND PANORAMIC PHOTOGRAPHY

  2. Projection

  3. Projection

  4. Vertical vanishing point (at infinity) Vanishing line Vanishing point Vanishing point Vanishing Points Slide from Efros, Photo from Criminisi

  5. Vanishing point calibration

  6. Vanishing point calibration • Advantages: • only need to see vanishing points(e.g., architecture, table, …) • Disadvantages: • not that accurate • need rectahedral object(s) in scene Structure from Motion

  7. Resectioning Resectioning: correspondence between 3D and image entities

  8. How does a camera work ? *3

  9. Image formation • Let’s design a camera • Idea 1: put a piece of film in front of an object • Do we get a reasonable image?

  10. Pinhole camera • Add a barrier to block off most of the rays • This reduces blurring • The opening known as the aperture • How does this transform the image?

  11. Camera Obscura • The first camera • Known to Aristotle • How does the aperture size affect the image?

  12. “circle of confusion” Adding a lens • A lens focuses light onto the film • There is a specific distance at which objects are “in focus” • other points project to a “circle of confusion” in the image • Changing the shape of the lens changes this distance

  13. Lenses • A lens focuses parallel rays onto a single focal point • focal point at a distance f beyond the plane of the lens • f is a function of the shape and index of refraction of the lens • Aperture of diameter D restricts the range of rays • aperture may be on either side of the lens • Lenses are typically spherical (easier to produce) F focal point optical center (Center Of Projection)

  14. Thin lenses • Thin lens equation: • Any object point satisfying this equation is in focus • What is the shape of the focus region? • How can we change the focus region? • Thin lens applet: http://www.phy.ntnu.edu.tw/java/Lens/lens_e.html (by Fu-Kwun Hwang )

  15. Depth of field • Changing the aperture size affects depth of field • A smaller aperture increases the range in which the object is approximately in focus f / 5.6 f / 32 Flower images from Wikipedia http://en.wikipedia.org/wiki/Depth_of_field

  16. Range of tools Digital Survey > Dimensional> indirect (photographic) Scaled-rectified photography: 1. Referencing Total Station To measure Controls: Targets for rectified photography (b) (a) (b) The Total station is located by indicated location (a) and orientation (b) (a) Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm

  17. Range of tools Digital Survey > Dimensional> indirect (photographic) Scaled-rectifiedphotography: 2. Measuring controls Controls: Targets for rectified photography are measured with the total station Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm

  18. Range of tools Digital Survey > Dimensional> indirect (photographic) Scaled-rectifiedphotography: 2. Measuring controls If a total station is not available, we can triangulate the controls, measure them by disto or tape Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm

  19. Range of tools Digital Survey > Dimensional> indirect (photographic) Scaled-rectifiedphotography: 3. Taking a parallel photography A photo is taken covering the fabric with 5 targets Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm

  20. Range of tools Digital Survey > Dimensional> indirect (photographic) Scaled-rectifiedphotography: Specialized Software 5. Reducing the distorion of the photography Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm

  21. TECHNOLOGY: Digital Survey > Dimensional> indirect (photographic) Scaled-rectifiedphotography: 6. Results: digitizing the photograph Photoplan: http://www.photoplan.de - Trextify: http://www2.asro.kuleuven.ac.be/asro/english/HOME/BVG/index.htm

  22. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA RECTIFIED PHOTOGRAPHY NOT RECOMMENDED FOR Irregular surfaces - Circular surfaces 4 PAGE MODULE 4: SCALERECT-PHOTO

  23. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA RECTIFIED PHOTOGRAPHY Surfaces 1 Each surface requires recti cation 1 2 3 4 5 2 3 4 5 5 PAGE MODULE 4: SCALERECT-PHOTO

  24. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA RECTIFIED PHOTOGRAPHY Reducing perspective distortion Vertical tilt of camera is not recommended Optimal position Slide courtesy of Christian Ouimet, Public Works Canada 6 PAGE MODULE 4: SCALERECT-PHOTO

  25. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA RECTIFIED PHOTOGRAPHY Reducing perspective distortion Use of a shift lens Reduce perspective Elevate camera by use of adjacent building or crane May be challenging keeping camera perpendicular to building 7 PAGE MODULE 4: SCALERECT-PHOTO

  26. Digital Survey > Dimensional> indirect (photographic) Scaled - Rectifiedphotography • How to reduceperspective – Same rules apply to horizontal perspective – Use manual exposure when producing a mosaic Slide courtesy of Christian Ouimet, Public Works Canada

  27. Digital Survey > Dimensional> indirect (photographic) Scaled - Rectifiedphotography Slide courtesy of Christian Ouimet, Public Works Canada

  28. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA IMAGE ISSUES Radial distortion is a failure of a lens to be rectilinear: a failure to image lines into lines. If a photograph is not taken straight-on then, even with a perfect rectilinear lens, rectangles will appear as trapezoids: lines are imaged as lines, but the angles between them are not preserved (tilt is not a conformal map). This e ect can be controlled by using a perspective control lens, or corrected in posprocessing Issues: Perspective distortion is a warping or transfor- mation of an object and its surrounding area that di ers signi cantly from what the object would look like with a normal focal length. Perspective distortion can typically be seen in images shot using a wide angle of view, where an object close to the lens appears abnormally large relative to more distant objects, or in distant shots with a narrow angle of view, where the viewer cannot discern relative distances between distant objects and more distant objects may look exceptionally large, when such images are http://en.wikipedia.org/wiki/Distortion_(optics) - http://en.wikipedia.org/wiki/Perspective_distortion_(photography) http://www.dxo.com/us/photo/dxo_optics_pro/optics_geometry_corrections/distortion 10 PAGE MODULE 4: SCALERECT-PHOTO

  29. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA LENS DISTORTION For appropriate products in recti ed photography, lens distortion should be minimized. There are two main types of lens distortion: radial and tangential distortion. Since the amount of tangential distortion is neglible for simple recti cation procedures, this procedure only concentrate on removing radial distortion Image with radial distortion Image without radial distortion Radial distortion coe cients should be identi ed during calibration process 12 PAGE MODULE 4: SCALERECT-PHOTO

  30. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA CAMERA CALIBRATION USING 2D PATTERNS Distance of squares (ex. 29 cm) Distance of squares (ex. 29 cm) Number of squares between 1 and 2 (ex. 11) 1 2 Number of squares between 1 and 4 (ex. 7)) 3 4 CAMERA POSITION CAMERA POSITION CAMERA POSITION CAMERA POSITION CAMERA POSITION CAMERA POSITION CAMERA POSITION CAMERA POSITION 13 PAGE MODULE 4: SCALERECT-PHOTO

  31. KAHOSL - PHOTOGRAMMETRY SYLLABUS 2009-2010 - M. SANTANA SCALE RECTIFY PHOTOGRAPHY AND CAD OVERLAY A CAD package is used to overlay the geometry of the feature 16 PAGE MODULE 4: SCALERECT-PHOTO

  32. SCALE RECTIFY PHOTOGRAPHY AND CAD OVERLAY • D the distance to the object (in mm) • f the equivalent 35mm camera focal length (in mm) • N the total number of pixels of the taken photograph. •  f the equivalent 35mm camera focal length (in mm)  http://www.dpreview.com/reviews/specs.asp

  33. SCALE RECTIFY PHOTOGRAPHY AND CAD OVERLAY • Example • Canon Eos 400d (sensor size of 22,2 x 14,8 mm) • image from a distance of 10 meter • Using the full 10 MP • focal length of 28mm • Convert Focal length to 35mm equivalent • For most cameras this can be done by multiplying the focal length by 36 and then dividing the result by the width of the sensor. • Put everything into formula • RESULT : 1 pixel = 1,274 mm in reality

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