کالیبراسیون دوربين

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011111110000 

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2 قبل از استفاده از هر دوربينى يارامترهاى ثابت دوربين را كاليبره مى كنند. 9 1 1 این پارامترها عبارتست از : ‎-١‏ مختصات نقطه اصلى ‏۲- فاصله کانونی دوربین ‎| ‏؟- مختصات فيدوشال ماركها و فواصل بين آنا ‎SN‏ ۹ 

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CALIBRATION » Assignment of numbers to represent properties that describe the metric 6220161151165 01 ‏عط‎ 222511176126121 0 and describe the quality of the performance ® Concepts * Component concept - assess quality of different components within photogrammetric process © System concept - take into consideration the ۳۹ photogrammetric process ۹ 

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CALIBRATION (cont.) * Classes ® Laboratory - outgrowth of manufacturers ® Visual approach - optical goniometers ° Photographic approach - bank of optical collimators ° Field ° Horizon method - only horizontal angles measured ©» Full field method - horizontal & vertical angles measured ° Stellar method - use star field as control 5200 - results in measurement system from which comparisons can be made ° Prepare system specifications by precisely defining 3 the measurement system ° Exercise system by comparing results to known 4 values of higher quality and assess the results 2 

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Len NEE TIE MUTT US ene بيشتر شركتهاى توليد كننده دوربين به دليل دقيق بودن 5 8 أزمايشكافى استفاده مى قت 

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Banks of collimators Front node Rear node Focal plane FIG 1. Multi-collimator calibration scheme. 

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Mirror Auto collimato: Camera Graticule سا Camera Collimator Light rays 

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۱۹ Asa aCe COR Ey eer poets 3 — و 5 ۱ 7 خر امرخ روش بر روی صفحه کانونی دوربین یک شبکه مشبک تعبیه می شود و از پشت به آن نور تابانده می شود 1۳ Sr eM CSI Cras acc. ae ‏با استفاده‎ ea ‎your‏ اندازه ‎ee‏ مى شود. 

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Illuminated grid Camera limator Measured angle FIG 2. The moving collimator goniometer principle. 

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Horizontal axis of rotation, Vertical axis of | rotation 0» 

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و ۱۹ 

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Camera 

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OPTICAL GONIOMETER * Center precise grid plate in camera focal plane © Grid illuminated from rear and projected through cameral lens ® Angles to projected grid rays emerging ‎from lens measured‏ يه ‎ert a goniometer‏ ‎a. 

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CAMERA CALIBRATION ® Determine precise & accurate values for elements of interior orientation * Calibrated focal length (CFL) ° Focal length producing mean distribution of lens distortion ©» Really a calibrated principal distance ® Symmetric radial lens distortion ® Occurs along radial lines from principal point ® Decentering lens distortion ° Further broken into asymmetric radial and tangential 2 * 0311560 ‏قط‎ manufacture imperfections and lens alignment 2 

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CAMERA CALIBRATION (cont.) ® Principal point ® Resolution 1200 » 5121011655 017 ‏ع من‎ 015 principal point w.r.t the fiducial marks » 210151 2621 0211 ® Fiducial mark * Focal plane flatness coordinates * Deviation of platen ‏ان‎ from true plane _ reference for principal © Shutter efficiency .. point as well as er ‏ا‎ on the photo ‏تیان‎ ‏ا‎ correctly 

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FOCAL LENGTH ® Nominal » focal length classification ® Equivalent (EFL) ° Effective focal length near center of camera lens ©» Calibrated (CFL) © Also called camera constant © Adjusted value of EFL - distribute lens distortion , over entire field of camera 

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PRINCIPAL POINTS Fiducial Marks ® Indicated principal point (ipp) ° “fiducial center” or “center of collimation” ©» Intersection of opposite fiducials ® Principal point of geometric optics (ppgo) ® Point on optical axis at which the optical axis intersects 41 the principal plane 

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PRINCIPAL POINTS (cont.) ® Principal point of photogrammetry (ppp) ¢ Foot of perpendicular from the interior perspective center to the plane of the photograph ® Principal point of autocollimation (ppac) * Intersection point of a ray with the plane of the photo for that ray which is perpendicular to the focal plane prior to passing through the lens ppac ۲ Focal Plane ent light ray Incident li y at Camera Lens 5 ba ‏د ا‎ 6 

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PRINCIPAL POINTS (cont.) ® Principal point of symmetry (pps) ° “calibrated principal point” ® Point in focal plane about which all lens distortion are most nearly symmetrical © Can only be approximated when decentering distortion is present ® Principal point of minimum variance (ppmv) ° Numerical values adopted for the photo origins in _ terms of fiducial centered coordinates usually ۹ ‏متي‎ from a least squares adjustment 

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eo 

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COLLIMATOR METHOD 

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CAMERA CALIBRATION (cont.) ¢ Simple approach to calibration * Compute equivalent focal length ۳ $559 tan 7.5° ©» ‏و‎ = measured distance from principal point to collimator target ®a = angle from principal point to collimator target 86 

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CAMERA CALIBRATION (cont.) * Compute diagonals to the other crosses s'. = EFL tana, ®* where i= 15°, 22.5°, 30°, 37.5°,45°, ® Compute distortions at each point d, =s, —s';=s, —EFL tana, 

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{s, -CFLtana, }+{s, —CFLtana, }=0 s, +s, =CFL (tana, + tana, ) CFL = 5, +S, tana, + tana, 

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CAMERA CALIBRATION (cont.) ‎data from‏ ی ‎collimator observations‏ ‎ ‎ ‎ ‎Angular Value 116251110 172111 (degrees) (mm) ۳,2 203 1.5.0 AL L77 Peas) 63.663 30.0 88.726 5 87.5 117.866 i, 050 153.435 ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ 

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=153.609mm d = 41.177mm- (153 0) )t an15° =+0.018mm = 63.663 mm — (153.609 mm )tan 22.5° = +0.036mm yor = 88-726 mm — (153.609 mm)tan 30° = +0.040 mm ‎mm — (153.609 mm)tan 37.5° = —0.002 mm|‏ 117.866 = م ‎( ‎( ‎1 ‏ور‎ = 153.435mm-— (153.6 m )tan 45° = —-0.174mm ‎ 

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26mm + 153.435 mm tan 30° + tan 45 = 153.5 24 mm)tan 7.5° = +0.011 mm .524mm)tan15° = +0.040mm 24 mm )tan 2 = + lmm d,,. =88.726mm — (153.524mm)tan 30° = +0.089mm 4 6mm — (153.524mm)tan 3 

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LINE COUNT METHOD * Photograph resolution — test pattern — 1 ۰ ‏لا‎ ‎©» 12236065 6223121260 under — magnification | | | ‏فح‎ 2 ©» Find finest set of parallel — lines discernable ی ‎Resolution (AWAR)‏ ® Resolution over entire ۱۱۱23 = sil= ۱۱/24 ‏2د‎ ‎3 10 ||| -5 6۱۱۱ 

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۱۱۱۱ 27 1 “LUA ZAM اون 

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DIGITAL FRAME CAMERA CALIBRATION * CCD elements essentially fixed in position * Initially, each pixel assumed to be in perfect grid ® Calibrate using two-dimensional transformation * Upper limit of resolution absolutely fixed ® Sampling into discrete elements ® Maximum spatial frequency: ۱۱ ‏ات‎ ‎Md 2 max detectable frequency 

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DIGITAL FRAME CAMERA Example ¢ Example: Digital frame camera consists of 5120 x 5120 pixel array. Pixel size = 12 pm. Nominal focal length = 40 mm. ® What is maximum spatial frequency that can be detected (at image scale)? ® What is the angular field of view for this ‏و9‎ 

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DIGITAL FRAME CAMERA Example (cont.) 1 ! = 42 cycles/mm MAX = ‏و2‎ = 2(0.012mm) 

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خلاصه اين فصل “انواع روشهاى كاليبراسيون 

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۱ ۱۱۱0۱100۱10۱۱۵ 11 ° Robert Burtch (Center for Photogrammetric Training) Ferris State University ۹ ۱ 

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پایان فصل ۳۴ 

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روشهای کالیبراسیون دوربین “روش آزمايشكاهى ‎(Orr nas ail‏ ‎(ian eastaci ct an‏ “روش ستاركان ‎a <‏ ۱ ‎eer Own by‏ ‎AX aC cameos‏ * 

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روش صحرایی و روش حین پرواز | زمینی برای محاسبه پارامترهای کالیبراسیون است. روش حین پرواز : در اين روش پروازهای متعددی بر روی منطقه اى كه داراى نقاط مشخص زمينى در جهت هاى مختلف انجام مى كيرد. از اين روش قابل بسط دادن به خالتی است که در لن پارامترهای کالیبراسیون همراه با عکسبرداری در یک کار واقعی قلبل محاسبه کردن می باشد ۱ SN ype Cet ۱6 eae cea Ba PAN Lean ea ‏که به أن‎ 3