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Principles of Photogrammetry

By: Michio Clark. Principles of Photogrammetry. What is Photogrammetry. The art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring and interpreting images

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Principles of Photogrammetry

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  1. By: Michio Clark Principles of Photogrammetry

  2. What is Photogrammetry • The art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring and interpreting images • A system which is called photogrammetric has to meet the following requirements • Capability for self-diagnosis • Potential for high precision and reliability • Task flexibility with respect to 3-D object reconstruction functions Click View then Header and Footer to change this footer

  3. Photogrammetry in Biomechanics • Can be used to solve two major measurement problems • Reconstruction of surfaces • Eg body, face, etc. • Determination of trajectories of moving targets • Can be combined with data for other sensors to make hybrid system solutions Click View then Header and Footer to change this footer

  4. Triangulation • Used to produce 3-dimesnsional point measurements • Two frames is the minimum requirement to be able to reconstruct an object in 3-D • Two-dimensional (x,y) location of the target on the image is measured to produce lines of sight • Lines can be mathematically intersected to produce (X,Y,Z) coordinates of each target point Click View then Header and Footer to change this footer

  5. Field of View • The rectangular area seen by the recording medium (film, video) after passing through the camera’s optics • Angle of view • Horizontally • Vertically • Diagonally Click View then Header and Footer to change this footer

  6. Importance Aspects to Consider • Motion before and after the period of interest must be recorded • Digitizing system used to quantify the motion may reduce the recorded field of view • Motion at the edges of the image may be distorted Click View then Header and Footer to change this footer

  7. Film Plane • The plane inside any camera with a lens which the film or digital sensor is located • In a properly designed camera the film plane is the same plane as the focal plane • The distance of the film plane varies based on the focal length of the lens Click View then Header and Footer to change this footer

  8. Principal Distance • The distance between the lens plane and the image plane • The camera’s distance setting should be set equal to the principle distance Click View then Header and Footer to change this footer

  9. Methods to Set Principle Distance • Autofocusing • Focus with participant standing in the middle of the field of view • Then turn off autofocusing • Manual • Measure the distance form the camera to the plane of motion • Set this distance manually on the lens Click View then Header and Footer to change this footer

  10. Calibration of Imaging System • Calibration must be used to ensure that the image coordinates are correctly scalded to size • The aim is the determination of parameters of interior orientation plus additional parameters, x0, y0, c of a particular camera or photograph • Elements of interior orientation • The position of perspective centre with respect to fiducial markers • The coordinates of the fiducial marks • The calibrated focal length of the camera • The radial and discentering distortion of the lens assembly • Image quality measures such as resolution Click View then Header and Footer to change this footer

  11. Methods of Calibration • 2-D system with one camera • Use a calibrated ruler or surveyor's rod place in the participant’s plane of motion • Scaling factor(s) can be determined for both directions (X,Y) Click View then Header and Footer to change this footer

  12. Methods of Calibration • Multicamera systems • Establish a series of control points • For 2-D analyses, at least four noncollinear points are required • For 3-D analyses, at least six noncoplanar locations on a 3-D structure are required Click View then Header and Footer to change this footer

  13. Accuracy of Calibration • Most accurate calibrations are seen when the control points are evenly distributed across the control region • Accuracy of 3-dimensional calibration increases as the number of control points increase form 8 to 24 • At 16 points the system starts to stabilize • Large errors can be seen at the corners of the calibration frame Click View then Header and Footer to change this footer

  14. Fractional Linear Translation (FLT) • Permits scaling form digitizer to real units • Permits differential scaling in X and Y directions • Removes rotations about all three axes or any combination • Cannot remove angular distortions (pins cushions or barrel) Click View then Header and Footer to change this footer

  15. FLT Equation • to are the coefficients of the FLT • and are the digitized marker coordinates • and are the marker’s refined coordinates in metric units Click View then Header and Footer to change this footer

  16. References Chen L, Armstrong CW, Raftopoulos DD, An investigation of the accuracy of three-dimension space reconstruction using the direct linear transformation technique, J. Biomechanics, 27, 4, 493-500, 1994 DaPena J, Harman EA, Miller JA, Three-dimensional Cinemtography with control objext of unknown shape, J. Biomechanics, 15, 1, 11-19, 1982 Francisco A, Continuous prinicipal distance change for binocular depth perception, Image and Vison Computing, 13, 2, 101-109, 1995 Gruen A, Fundamentals of videogrammetry – a review, Human Movment Science, 16, 155-197, 1997 Northey NW, The angle of view of your lens, In Frank V. Chambers. The Camera, Columbia Photographic Society, 20, 9, 1916 Robertson DGE, Caldwell, GE, Hamill J, Kamen G, Whittlesey SN, Research Methods in Biomechanics, 13-17, Human Kinetics, Campaign, 2004 Schenk T, Introduction to photogrammetry, Department of Civil and Eniromental Engineering and Geodetic Science, The Ohio State University, Autum Quarter 2005, http://www.mat.uc.pt/~gil/downloads/IntroPhoto.pdf Woltring HJ, Planar control in multi-camera calibration for 3-D gait studies, J. Biomechanics, 13, 39-48, 1980 Chapter 10 principles of photogrammetry, EM 1110-1-1000, March 31st 1993, http://gisceu.net/pdf/u5r.pdf The Basics of Photogrammetry, Geodetic Systems, http://www.geodetic.com/v-stars/what-is-photogrammetry.aspx, 2013-10-25 Click View then Header and Footer to change this footer

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