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# camera calibration

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Sandeep sasidharan

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### camera calibration

1. 1. Presented by: Sandeep Sasidharan IIT Kanpur
2. 2.  Purpose of camera calibration Calibration distortion models Methods of calibration
3. 3.  Determine the IOP of camera  Focal length (f)  The principal point co-ordinates (x0,y0)  Image distortion parameters
4. 4.  For carrying out photogrammetry  Camera lens must provide perfect central projection  Camera focal plane is perfectly flat OR  Camera lens perspective centre, the ground point and the corresponding point on the image lies in a straight line
5. 5.  Radial lens distortion (RD) Decentric lens distortion (DLD) Atmospheric refraction distortion (ARD) Affine deformation distortion (ADD)
6. 6.  Laboratory methods Field methods Stellar methods
7. 7. Wolf, P.R.,(Elements of photogrammetry)
8. 8. Wolf, P.R.,(Elements of photogrammetry)
9. 9.  Equivalent focal length  FL at distortion free central area of lens  EFL= (gf+ gh+ gs+ gt)/ 4 tan θ Radial lens distortion of each angle θ  RD=EFL x tan n θ ( theoretically for angle n)  Directly measured and averaged ( practical value)  Difference of both gives RD for each angle
10. 10.  Calibrated focal length  FL which produces mean distribution of RD  CFL is selected so that Max +ve RD = Max –ve RD (D1-CFL tan θ1 + D2-CFL tan θ2 )=0 Principal point location
11. 11.  Target points are near to the centre and sparse in outer areas and radial distortion is predominant at outer areas Method is very expensive Measurements must be very accurate
12. 12.  Self calibration Calibration using 2D/3D calibration objects Bundle Adjustment Method
13. 13.  Development of new algorithms for IOP determination Helped using less expensive digital cameras for conventional photogrammetry