REAL-TIME-PHOTOGRAMMETRY BY MEANS OF HIGH-SPEED-VIDEO

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Stuart Potter
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1 REAL-TME-PHOTOGRAMMETRY BY MEANS OF HGH-SPEED-VDEO Wil Wester-Ebbinghaus nstitut fur Phtgrammetrie und Bildverarbeitung der Technischen Universitat Braunschweig GauBstraBe 22, 3300 Braunschweig ic f Germany Heinz Zamzw Hentschel GmbH Frankische Str. 62, 3000 Hannver 91 f The paper describes a phtgrammetric real-time system. Randmaccess vide cameras are used, which allw pint tracing with a frequency up t 7 KHz. A strategy fr simultaneus numerical full system calibratin is encluded. ntrductin The class principal f phtgrammetry, the distingtin between the bject recrding n site and the bject restitutin in the labratry, has been prved very useful. The analgue phtgraphic images prvide metric dcuments f high quality, which allw the measurement at any time, while the recrding effrt n site is lw. Recently develped analytical restitutin techniques allw t use the pssibilities f prfessinal phtgraphy, thus encreasing the range f applicatins cnsiderably. n industrial phtgrammetry hwever, it is ften necessary t get the metric infrmatin n site, rather than t get a metric dcument. CCD-imaging-systems are already used t realize phtgrammtric n-line and even real-time systems (E-Hakim 1986, Luhmann and Wester-Ebbinghaus 1986, Beyer 1987, Gttwald and Berner 1987, Haggren 1987, Wester-Ebbinghaus 1988). CCD-vide with an imaging frequency f 30 Hz is nt suitable in rder t recrd fast prcesses. The paper presents a randmaccess vide system, which allws high speed bject recrding. First results prve the system suitable fr phtgrammetric applicatins. A randm-access tracking system Fig. 1 shws the principle f a randm-access vide camera. The rays transmitted frm the image plane (cathde) are scanned lcally and fcused t the ande. The lcal recrding allws high frequency pint tracing in the image plane. 1

2 randm access camera ande fcussing image plane cathde Fig. 1: Principal f randm-access vide tracking Fig. 2: Hentschel randm-access tracking system HSG with Hamamatsu camera C Halgen lamps fr illuminatin f retr reflecting targets 13

3 a) multipint randm-access scanning in the field f view y +- f l-, [ 1\ V -- --r-- "- / ~ \ -- "./ ~, ' 1-1- r- l- - X b) high frequency sinus scanning inside a windw Fig. 3: Randm-access windw scanning V-214

4 WNDOW SCAN X SEARCH UNT HOST CO"lP V-SCAN GENERATOR CENTER ARTHMETC UNT Y WNDOW SCAN Y Fig. 4: Blckdiagram f vide-interface EJ HAMAMATSU CAMERA HEAD r------, : EXTERN : : WNDOW CONTROL L J HENTSCHEL VDEO - NTERFACE EJ HAMAMATSU CAMERA HEAD X/YCENTER OOORDNA TES HOST COMPUTER Fig. 5: Blckdiagram f randm-access tracking system HSG V

5 The randm-access tracking system HSG frm Hentschel System allws high speed and high reslutin multi-pint tracking (Zamzw 1988) (fig. 2). This system uses randm-access cameras C 1181 frm Hamamatsu Phtnics with an image dissectr. n cntrast t cnventinal vide cameras with nrmal TV scanning its scanning mde is nt limited by synchrnizing signals. This allws a free extern deflectin. By setting windws (fig. 3) instead f full screen mde with cmparable abslute deflectin speed inside, the sampling rate can be extremely increased. Because the image dissectr has n lag, the camera can access any pint in the field with an access time under 15 micrsecnds. Thus, sampling rates up t 7,5 khz are pssible. The picture frequency depends n the number f windws, which is variable. The reslutin f the camera system is 8192 x 8192 pixels. With reduced dimensin f th~ tracking windws - smaller then 1% x 1% f the field - even a higher reslutin is pssible. The nise is less then +/-4 pixels at 7,5 khz sampling rate, small windws and best light cnditins. By reducing the variable sampling rate, a lnger access time and a finer scanning will imprve this value. The functin f the vide-interface fra tw dimensinal measurement is shwn in the blckdiagram fig. 4. Befre tracking is started, the psitins f the pints are autmatically detected in a special search line mde and stred in the tracking memry. After change-ver t tracking mde, the marks are surrunded by windws (fig. 3a). The high speed deflectin signals (fig. 3b) are digitally generated by the x/y scan generatrs. The vide-signals f the camera allw t detect the peripheral crdinates inside the windw with a reslutin f 8 bits. A fast hardware arithmetic unit cmputes the centers f the pints. The additin f the windw psitin and the center psitin inside the windw delivers the pint psitin in the field f view. The x/y-crdinates are stred in the tracking memry and used fr windw placing in the next frame (fig. 3a). The extremely reduced quantity f data allws a simultaneus n-line data transfer t a hst cmputer even at highest sampling rates. Variable sampling rate, windw dimensins and number f windws enable the user t ptimize the system t different prblems f measurement. The vide-interface allws multi-camera tracking with synchrnus cntrl fr 3-D mtin analysis and n-line data transfer t a cmputer (fig. 5). Phtgrammetric applicatin - First experiences By means f a multi-image test field triangulatin the gemetric quality f the randm-access vide system was investigated. The test field, cnsisting f 25 pints equipped with retr-reflecting targets, was recrded by 10 images accrding t fig. 6.The illiminatin was realized by halgen lamps, arranged as shwn in fig. 2. A bundle triangulatin, carried ut as a free net adjustment, led t the fllwing results: a : ± 7 pixel relative accuracy in bject space ~

6 Q y x Fig. 6: Test field triangulatin OBJECT PONT RANDOM ACCESS CAMERAS STORAGE OBJECT COORDNATES Fig.. 7: ntegrated system fr phtgrammetric multi-camera randm-access pint tracking V-217

7 Blck invariant additinal parameters were intrduced fr affine and radial-symmetric distrtin. The accuracy may be encreased by means f additinal parameters, specially designed in rder t describe the image defrmatins f randm-access vide. This requires a suitable strategy fr system calibratin. Fig. 7 shws a prpsal fr an integrated phtgrammetric multi-camera randm-access tracking system: The cameras can be calibrated within bundle adjustment. Recrding the cntrl infrmatin in real-time, the calibratin intervals may be chsen accrding t the instrumental cnditins and the accuracy demands. Further mre the scheme in fig. 7 allws t supprt the real-time pint tracking by means f respnse frm the bject, reprjecting the determined bject pints numerically int the image systems. This allws t recatch a pint, when the tracking had been interupted in a camera. Cnclusins The presented randm-access vide system allws pint tracking with a frequency f abut 7 KHz. The gemetric quality f the images is suitable fr phtgrammetric applicatins. The accuracy f ~ 10-3 achieved in the first tests may be encreased by means f calibratin strategies, specially develped fr randm-access vide. References Beyer, H.A., 1987: Sme Aspects f the Gemetric Calibratin f CCD-Cameras. SPRS Cnference "Fast Prcessing f Phtgrammetric Data", nterlaken. El-Hakim, S.F., 1986: A Real-Time System fr Object Measurement with CCD-Cameras, SPRS Sympsium Cmmissin V, Ottawa. Fraser, C, Brwn, D.C., 1986: ndustrial Phtgrarnrnetry-New Develpments and Recent Applicatins. The Phtgrammetric Re crd 1 2 ( 68).. Gttwald, R., Berner, W., 1987: Electrnic Thedlites-Sensr Systems fr Real-Time-Phtgrarnrnetry? SPRS Cnferences "Fast Prcessing f Phtgrammetric Data", nterlaken. Haggreen, He, 1987: Mapvisin - The Phtgrammetric Machine Visin System. SPRS Cnference "Fast Prcessing f Phtgrammetric Data", nterlaken. Luhmann, T., Wester-Ebbinghaus, W., 1987: Digital mage Prcessing by Means f Reseau-Scanning. 41st Phtgrarnrnetric Week, Stuttgart. Wester-Ebbinghaus, W., 1988: Trends in Nn-Tpgraphic Phtgrarnrnetry Systems. n: Karara, S. (Editr): Handbk f Nn-Tpgraphic Phtgrammetry, 2nd editin, ASPRS. Zamzw, He, 1988: Schnelle Bewegungen in Echtzeit erfassen. Elektrnik, 4/88. V

APPLICATIONS: TELEVISIONS

APPLICATIONS: TELEVISIONS CATHODE RAY TUBE A cathde ray tube (CRT) is a specialized vacuum tube in which images are prduced when an electrn beam strikes a phsphrescent surface. Mst desktp cmputer displays make usef CRTs. The CRT