ESTIMATION OF INTERIOR ORIENTATION AND ECCENTRICITY PARAMETERS OF A HYBRID IMAGING AND LASER SCANNING SENSOR

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1 ESTIMATION OF INTERIOR ORIENTATION AND ECCENTRICITY PARAMETERS OF A HYBRID IMAGING AND LASER SCANNING SENSOR A. Wendt a, C. Dold b a Insttute for Appled Photogrammetry and Geonformatcs, Unversty of Appled Scences Oldenburg, Ofener Straße 16/19, D Oldenburg, Germany a Insttute of Photogrammetry and GeoInformaton, Unversty of Hannover, Nenburger Str. 1, D-3167 Hannover, Germany b Insttute of Cartography and Geonformatcs, Unversty of Hannover, Appelstr. 9A, D-3167 Hannover, Germany (a.wendt@fh-oldenburg.de, chrstoph.dold@kg.un-hannover.de) Commsson V, WG V/1 KEY WORDS: Calbraton, Terrestral laser scannng, Hybrd measurement system, Sensor fuson ABSTRACT: Nowadays hybrd magng and laser scannng sensors are common for terrestral surveyng purposes. The basc dea s to complement laser scannng, whch drectly yelds 3D nformaton, wth dgtal mage capture, whch delvers hgh resoluton mages for measurement and texturng. The mage sensors are nternally bult n a scanner or externally mounted on top. The advantage of external mounted devces s the flexblty of the used sensors. Dependng on the applcaton, cameras wth a dfferent resoluton or focal length can be used. Such systems are handy, but the calbraton parameters have to be determned or controlled for each sensor and every mount. Hybrd systems offer new possbltes such as monoplottng usng a combnaton of mages and 3D pont clouds or automatc orentaton procedures. Furthermore, the fuson of both data sources wll generally lead to a hgher accuracy and relablty. These facts emphasze the mportance of an accurate calbraton between the sngle sensors of a hybrd system. The calbraton can be subdvded nto three tasks, calbraton of the scannng system, the magng sensor and the estmaton of the eccentrcty between the sensors. Whle scannng systems are usually calbrated by the manufacturer, the calbraton of the magng sensor and the estmaton of the eccentrcty have to be done on the job by the user wth provded calbraton software. These calbraton tasks are dscussed n detal n ths paper. Based on the fact that the camera s mounted on the scanner, a comparson between sngle mage and multple mage calbraton s done regardng to the accuracy. The comparson s realzed wth a sutable 3D test feld, as t s used n close range photogrammetry. The dfferences of the sngle mage calbraton to the multple mage calbraton as reference values are gven. The sngle mage calbraton s about three tmes worse n nner and outer accuracy. Further manly for the eccentrcty, a three-dmensonal test feld s created. In a practcal test the eccentrcty calbraton wth and wthout commonly adjusted camera calbraton parameters s evaluated. It s emphaszed that the eccentrcty parameters are hghly correlated wth the nteror orentaton parameters. The most relable result of the eccentrcty calbraton could be obtaned by ntegratng the nteror orentaton of the multple mage calbraton fxed. 1. INTRODUCTION 1.1 Terrestral Laser scannng Terrestral laser scanners become more and more popular for surveyng purposes. There are many dfferent applcatons where such scanners are used, for example montorng, documentaton of monuments and hstorc buldngs, data acquston of buldngs as a bass for cty modelng or ndoor measurements n buldngs. Terrestral laser scanners provde a dense three dmensonal pont cloud of the scanned object. Most scanners work wth a smlar prncple. A laser-lght pulse s emtted, parts of t are reflected at an object and receved and regstered by the nstrument. The dstance s usually determned from the tme of flght of the laser pulse or n some cases by trangulaton (close range scanners). Most scanners measure wth a hgh scan rate. The laser beam s deflected by rotatng or oscllatng mrrors n the vertcal drecton. The horzontal deflecton s usually done by rotatng the measurement devce of the scanner. Modern scanners cover an area of 36 degrees horzontally and are often termed as panorama scanners for ths reason. The vertcal feld of vew s often lmted, but some models are able to scan a complete dome (up to 27 degrees). Terrestral laser scanners are classfed by ther maxmum measurement range. Usually they are dvded n three groups: close range, md range and long range scanners. There are consderable dfferences n the accuracy of the sngle measurements and the spot szes of the laser scanner nstruments.

2 The standard scannng procedure n practce s to poston the scanner system and to acqure data from the surroundng area. In order to obtan data of a complete object t s necessary to collect data from varous locatons. For each poston a new local coordnate frame s defned. The multple frames are usually transformed nto one common coordnate frame for data processng. 1.2 Hybrd Sensors Many scanner systems are equpped wth an addtonal mage sensor. The dstance measurement unt and the dgtal camera unt form a hybrd sensor system. Thus, mage data and 3D pont data can be combned. In general, to each measured 3D pont a color value acqured by the camera unt s assgned. Thereby the processng of the laser data s smplfed for human operators, because t s easer to relate colored ponts to objects. For nstance Becker et al. (24) descrbe a system for processng laser scannng and photogrammetrc data smultaneously. Furthermore the mages can be used for texturng models or objects, whch are derved from the laser scan data. The manufactures of laser scanners use dfferent technques for the combnaton of laser scanners wth dgtal cameras. One method s the ntegraton of a camera n the body of the scanner. In ths case scanner and mage sensor are combned to one unt. Examples are the GS seres from Mens (Mens, 25), Leca (Leca, 25) wth ts HDS3 scanner and Calldus (Calldus, 25). Another concept used by Regl for the LMS-Z seres (Regl, 25) and Qvoluton for the Qsun seres (Qvoluton, 25) for nstance, s to mount a dgtal camera externally on the top of the scanner. Both technques have several advantages and dsadvantages. The major drawback of externally mounted camera unts s the weak calbraton of such systems. Snce the dstance and camera unt are only connected by clampng system and are usually dsconnected for transportaton, the calbraton of the system should be done for each mount. The advantage les n the flexblty of the used sensors. Dependng on the applcaton, cameras wth a dfferent resoluton or focal length can be used for data acquston. Thus, the resoluton of dstance and camera unt may be adapted to each other. Ths paper s lmted to hybrd sensors wth externally mounted camera unts. A Regl LMS-Z36 scanner n combnaton wth Nkon D1 camera was avalable for measurements. The hybrd system s shown n fgure 1. scannng sensor. The scannng sensor tself s calbrated by the manufacturer. Frstly, we descrbe the requred calbratons of a hybrd scanner. Also the estmaton of the eccentrcty parameters between the sensors wll be explaned. In order to evaluate the qualty of the camera calbraton n comparson to beng mounted on the scanner or not, we compare mult and sngle mage calbraton usng a close range test feld. Ths s done under deal condtons n a laboratory test. In a practcal test, the eccentrcty s calbrated n a laboratory hall. There we have nstalled a test feld wth retro-reflected targets. Also the recommended calbraton method of the manufacturer to estmate the eccentrcty and mage calbraton smultaneously s done n ths test. Fnally, we conclude ths work and gve some statements to the resultng accuracy of the calbraton methods. 2. CALIBRATION METHODS The full system calbraton of a hybrd sensor can be separated nto three sngle calbratons: a) Calbraton of the scanner b) Calbraton of the eccentrcty c) Calbraton of the camera Usually the scanner s calbrated by the manufacture and wll not be dscussed here. The calbraton of the eccentrcty n contrast can only be done n combnaton wth the scanner. It wll be dscussed n detal. Therefore the mathematc model for the estmaton s derved. It s shown, that ths model could be extended wth the unknowns of each sngle sensor. The calbraton of the nteror orentaton of the camera should be done at the same tme of the measurement campagn. It s a standard photogrammetrc task n close range applcatons. 2.1 Calbraton of the eccentrcty Relaton between camera and laser scanner sensor As shown n fg. 1, the camera sensor s mounted on top of the laser scanner. The geometrc relaton between both coordnate frames s gven n fg. 2. Fgure 1: Combned sensor - laser scanner wth mounted camera (Regl, 25) We descrbe the calbraton of the nteror orentaton of the camera unt and the estmaton of ts eccentrcty to the laser Fgure 2: Relaton between ometrc (camera) and geometrc (laser scanner) sensor

3 The orgn of the coordnate frame of the geometrc sensor s defned as a rght handed system, the zero drecton of the horzontal ptch crcle defnes the x-axs. The defnton of the coordnate system of the geometrc sensor s also the defnton of the whole hybrd sensor system. On the other hand the orgn of the coordnate frame of the ometrc sensor s the projecton centre O '. Ths coordnate frame s defned by the camera. The orentaton of ths ometrc coordnate frame wthn the hybrd sensor system s descrbed by the eccentrcty between the sensors (fg. 1). The goal of the calbraton of the eccentrcty s the estmaton of three rotatonal and three translatonal parameters between the two coordnate frames. Thus, the eccentrcty ncludes sx degrees of freedom. However, n fg. 2 s also shown, that the observatons of the laser scanner and the mages are related to the object space by ther mappng functons. In case of the calbraton of the eccentrcty t s supposed that these functons are completely known. The mappng functons are: A ( d, φ, θ ) = geo (1) A ( e( T, R ), or, x', y')) = E E (2) Wth: geo 3D control pont n object space A Geometrc mappng functon θ d φ, Measured angles of the control pont Measured dstance to the control pont A Radometrc mappng functon ( T E, RE e ) Eccentrcty or ', y' Interor orentaton of the camera x Image coordnates of the control pont Calbraton For the calbraton of the eccentrcty a complementary aspect of the relaton between the sensors has to be ntroduced. An ndvdual rotaton angle of the ometrc sensor around the z- axs of the scanner s a part of the actual relaton between the sensors. Fg. 3 demonstrates ths connecton. The fgure shows the top vew of the scanner. Each poston of the ometrc sensor s observed by the already calbrated scanner. Thus the rotaton angle s treated as constant. By ths rotaton angle the mage frame s related to the x-axs of the geometrc sensor. The eccentrcty s defned between the sensors when the ometrc sensor s algned to the x-axs of the geometrc sensor. Fgure 3: observed rotaton for ndvdual camera poston In the calbraton of the eccentrcty the rotaton has to be consdered. It s represented n an ndvdual rotaton matrx R A rot j. The equaton (2) of the ometrc mappng functon s upged to: Wth: ( R, e( T, R ), or, x', y' ) = A (3) rot j E R rot Indvdual rotaton matrx j E Ths derved mappng functons show, that the calbraton of the ometrc and geometrc sensor can also be estmated n ths process. Therefore the mappng functons have to be extended wth unknown parameters of these sensors addtonally. The unknowns are the nteror orentaton of the ometrc sensor and e.g. correcton terms of the measured sphercal coordnates and dstance of the geometrc sensor. For demonstraton the extenson of the model s dscussed for the unknown nteror orentaton parameters of the camera. In ths connecton of calbraton task the camera has to stay mounted on top of the scanner. Because of the predctable poor camera confguraton n a smultaneous calbraton, the dfference between sngle mage and multple mage calbraton wll be shown n a laboratory test. 2.2 Interor orentaton When usng a dgtal camera for photogrammetrc tasks, a calbraton of the camera has to be done. Fraser (Fraser, 1997) gves an excellent overvew of a camera self-calbraton model. In a calbraton procedure, the parameters for nteror and exteror orentaton are determned. The nteror orentaton specfes the characterstc of the camera and s defned by the focal length of the lens, locaton of the mage s prncpal pont and dstorton parameters. The exteror orentaton descrbes the spatal relatonshp between the camera and object. The connecton between mage and object space s gven by the well known collnearty equatons (Luhmann, 23):

4 r11 ( x x + x = c r ( ( Y Y ( Y Y r21 ( 22 ( Y Y y y + y = c r ( ( Y Y ( Z Z ) ( Z Z ) ( Z Z ) ( Z Z ) The correctons coeffcents x and y nclude parameters modelng the al symmetrc lens dstorton and decenterng dstorton (Brown, 1971). Dependng on the camera, also affnty and shear should be consdered. The complete correcton term s: x = x + x + x d d aff y = y + y + y (5) aff Thereby the polynomal term of the al symmetrc correcton contans the parameters A 1, A 2, A 3, the tangental asymmetrc correcton s descrbed by B 1, B 2. The x-coordnate s usually also corrected by addtonal terms for affnty and shear. The terms account the dfferental scalng between horzontal and vertcal pxel spacng and model the non-orthogonalty between the x and y axes. Therefore the parameters C 1 and C 2 are used. Regl uses n ts software RScan Pro another camera model. It s smlar to the one used n the Open Source Computer Vson lbrary (Intel, 25). Here two potentally dfferent focal lengths (f x, f y ) are used to cope wth dfferent pxel szes n x and y drecton and to correct a cylndrcal lens error. Also up to four parameters for the al dstorton can be calculated. The decenterng dstorton s also modeled. The term for affnty s consdered by the dfferent focal lengths, but the shear s not ntegrated n the model. The relatonshp between the three-dmensonal object space and two dmensonal mages s gven by: u' f x v' = w' f y cx Y c y Rt Z 1 W (4) (6) Generally, n case of photogrammetrc calbraton, the accuracy of the nteror orentaton estmaton depends on: - The resoluton of the mage sensor, - The mage scale, - The accuracy of mage ponts, - The dstrbuton of control ponts - The dsposton of takng photographs The mage scale causes the sze of mapped control ponts n mage space. The resoluton of the sensor defnes the scannng frequency of the mage sgnal. The mage sgnal s dscretzed. One of the basc tasks s the exact determnaton of the control ponts n mage space. Therefore an nterest operator s needed. Interest operators for mage pont measurement acheve an accuracy of about.2.5 pxels (Luhmann 23). Also, a good dstrbuton of control ponts of the 3D test feld s necessary. The mage sensor should be covered completely by the mapped ponts for relably estmaton of dstorton. If the control ponts of the test feld are unknowns a mnmum of three mages are necessary (Maas, 1998). Also the camera has to be rotated between the postons of taken photographs to mnmze correlatons of the parameters of the nteror orentaton. For the calbraton a three dmensonal test feld wth a sze of about 1. x 1. x.4 m 3 s used (fg. 4). The control ponts of the test feld are estmated wthn a bundle adjustment of the multple mage calbraton. The lengths of three scale bars are ntegrated as addtonal observatons. For the taken mages an exposure tme of 1/8 sec. and an aperture sze of 8 are chosen. The mean dstance to the object s 15 mm. The focus of the 14 mm objectve s set to nfnty. In the laboratory envronment smlarly lght condtons as n possble outdoor applcatons are realzed. For the calculaton the software package Australs (Fraser, 21) and AICON 3D Studo (AICON, 25) are avalable. The mage coordnates u and v are also corrected by the lens dstorton. The parameters descrbng the dstorton are termed as k 1, k 2, k 3 and k 4 for the al, and p 1, p 2 for tangental correcton. In the followng both camera models are used: In the laboratory test the frst descrbed model and n the practcal test the second model. Anyway we wll not dstngush between these models further, because they can be transfered nto one another. Snce the dstorton parameters are hghly correlaton, t must be consdered that always the same parameter set have to be calculated for transformaton nto each another. 2.3 Laboratory test As mentoned n the begnnng of chapter 2 the dfferences between sngle and multple mage calbraton wth the aspects of relablty and accuracy should be demonstrated. The second goal n ths laboratory test s to determne the camera calbraton under deal condtons to acqure reference values for further nvestgatons. Fgure 4: Close range test feld Multple mage calbraton For the multple mage calbraton we choose an deal camera confguraton. Totally 16 mages are used for the bundle adjustment. The results of the nteror orentaton are:

5 parameter Values standard devaton C x y A e-4 A e e-6 A e e-8 B e e-4 B e e-4 C e e-3 C e-3 Table 1: Mult mage calbraton Sngle mage calbraton The sngle mage calbraton comples wth an adjusted resecton, where the parameters of the nteror orentaton are estmated, too. The coordnates of the test feld have to be known and are treated as constant. Here, the expanson of the test feld n all three dmensons s decsve for the estmaton of the camera parameters, because of the correlaton between the nteror and exteror orentaton. To mnmze systematc effects and to ncrease the relablty a large expanson of the test feld should be amed. The results of the nteror orentaton are: parameter Values standard devaton C x y A e-3 A e e-5 A e e-7 B e e-3 B e e-3 C e e-2 C e e-2 Table 2: Sngle mage calbraton Comparson of both calbratons The nner accuracy of the camera constant c and the prncpal pont x, y s more than two tmes hgher n the multple mage calbraton (tab. 1) than n the sngle mage calbraton (tab. 2). The relablty s much worse what s decsve for further applcaton. In the sngle mage calbraton the accuracy s drectly dependng on the accuracy of the control ponts. Further, there are less control purposes to determne blunders n the control ponts or mage ponts. The qualty of the estmated dstorton parameters s revealed by the coverage and dstrbuton of mage ponts on the sensor. a) Multple mage calbraton b) Sngle mage calbraton Fgure 5: Comparson of mage pont dstrbuton Fg. 5 shows the pont dstrbuton on the sensor. In both calbratons the coverage s not perfect. Especally n the mage corners ponts are rare. However, n the multple mage calbraton the coverage s more complete than n the sngle mage calbraton. To determne the outer accuracy of both calbratons a comparson n object space s necessary. In ths case the three scale bars are used. The lengths of the scale bars are known precsely wthn a standard devaton of 3 µm. The prevously determned control ponts wll be renserted fxed. The exteror orentaton of the mages s done wth the fxed ponts of the test feld. Now, only the targets of metrc scale bars are determned by spatal ntersecton. The dstance devaton between the known length value and the measured one s estmated. Ths s done wth the nteror orentaton of the multple mage calbraton and the sngle mage calbraton. For a more precse statement we let the nteror orentaton vary wthn ts accuracy and repeat the estmaton of the scale bar length. Ths s done about 1 tmes. The dfferences to the three scale bars (cf. fg 4) are shown n chart 1 and 2.,15,1,5 -,5 -,1 -,15 -,5 -,15 Scale bar 1 Scale bar 2 Scale bar Smulatons Chart 1: Dstance errors of mult mage calbraton,15,1,5 -,1 Scale bar 1 Scale bar 2 Scale bar Smulatons Chart 2: Dstance errors of sngle mage calbraton In tab. 3 the results are summarzed. Agan the accuracy of the multple mage calbraton s about three tmes hgher than of the sngle mage calbraton. In relaton to the frst two scale bars the thrd scale bar (cf. fg. 4) has worse accuracy. That ssued from the one sded vew of the targets. The bad confguraton of mage ray ntersectons mples naccurate length estmaton. Ths s confrmed by chart 1, where some dstances of the vertcally nstalled scale bar 3 have large varances. In the case of the sngle mage calbraton a decreasng accuracy s notced. Besde the three tmes worse

6 standard devaton also the amount of blunder n the estmated dstances s ncreased (cf. chart 2). mult mage sngle mage scale bar Mean devaton Standard devaton Table 3: Outer accuracy Contrary to the multple mage calbraton the results of the sngle mage calbraton are of less qualty. Besde the worse accuracy also bad relablty exsts. Errors n mage pont coordnates or control ponts affect the orentaton parameters drectly. The parameters of the nteror orentaton and exteror orentaton are hghly correlated. Also the coverage of mage ponts on the sensor wll be lower. 3. PRACTICAL TEST For the calbraton of the eccentrcty between both sensors a three dmensonal test feld was created n the laboratory hall of the Franzus Insttute of the Unversty of Hannover. Therefore 53 retro reflectve targets dstrbuted n 3D on the wall and grders of the hall roof serve as control ponts (fg. 6). The extenson of the test feld s about 5 m x 2 m x 1 m. The dstrbuton n the depth s excellent, but due to lmtatons n the accessblty of some parts n the hall, there are some holes n the lateral dstrbuton. Nevertheless, the quantty of the targets provdes very good condtons for calbraton tasks. For the calbraton of the eccentrcty, two cases have to be dfferentated. Frst, the nteror orentaton of the camera and the eccentrcty parameters are estmated smultaneously. The software provdes a system calbraton to estmate both n common. Second, the eccentrcty s determned wth a constant camera calbraton. Object ponts wth known coordnates are dentfed n at least one acqured mage. The correspondences between mage and 3D ponts are establshed and the eccentrcty parameters are calculated by the software. In ths practcal test, we carred out both methods to evaluate and demonstrate the dfferences between them. 3.1 Evaluaton of the nteror orentaton The estmated nteror orentaton of the system calbraton s compared to the nteror orentaton of the multple mage calbraton of the laboratory test. The results are shown n tab. 4. The values are n pxels. Unfortunately the software provdes only lttle nformaton about the accuracy of the calculated values. The output statstc contans only mean- and max-values of the resduals of the measured mage coordnates. Therefore only the parameters are shown. System calbraton [px] Multple mage calbraton [px] f x f y c x c y k k k k p p Table 4: Result of the nteror orentaton wth Rscan Pro The results of the system calbraton show notceable devatons from the other methods, especally n the prncpal pont. If the parameters are compared wth the reference values, the maxmum dfference of the dstorted pxel s about ten pxels n the edge of the sensor. The major reason for ths result s obvously the weak geometry of the camera s vew ponts. The dfference to the multple mage calbraton of the dstorted pxels for the whole sensor s shown n chart 3. Fgure 6: Test feld n the Franzus-Hall For the calbraton procedure the hybrd sensor was located n front of the test feld. From ths poston a laser scan s acqured and photographs wth the camera are taken n several postons by rotatng around the vertcal axs of the scanner. Fg. 6 shows the ntensty scan of the test feld and the dstrbuton of the control ponts. For the calculatons the software package RScan Pro (Regl, 24) of the scanner manufacture s used. There, operators for the extracton of correspondng ponts n the scan and the mages are provded by the software. In case of the pont extracton n the laser scanner data t should be notced, that n the addtonally recorded ntensty values the retro reflectve targets could be estmated precsely. Chart 3: Dfference of dstorton parameters to the multple mage calbraton

7 3.2 Evaluaton of the eccentrcty parameters The results of the eccentrcty parameters are lsted n tab. 5. Wthn the system calbraton the eccentrcty s calbrated wth the nteror orentaton. The three rotatons and translatons are shown n the frst row. Wthn the second eccentrcty calbraton the nteror orentaton of the multple mage calbraton s used. Rotatons Translatons Rot x [deg] Rot y [deg] Rot z [deg] T x [m] T y [m] T z [m] wth IOR wthout IOR dff Table 5: Results of eccentrcty calbraton In tab. 5 also the dfferences are stated. Due to further analyss we confrm that the dfferences especally n the rotatons wll be compensated wth the correspondng nteror orentaton. They are hghly correlated. In case of the nteror orentaton of the multple mage calbraton a better system calbraton has to be expected than n case of the common system calbraton whch comples to the sngle mage calbraton. 4. CONCLUSIONS In ths paper we showed how to deal wth the calbraton of a hybrd laser scanner wth a mounted camera. Several calbraton methods have been dscussed and analyzed, based on a hybrd sensor system from Regl, The results show, that the calbraton of the eccentrcty s hghly correlated wth the nteror orentaton of the camera. The scanner manufacturer (Regl, 24) recommends usng the calbraton method to estmate the eccentrcty and nteror orentaton n common. Another aspect of ther recommend method s to use a reduced vertcal test feld n a column that covers the camera s whole vertcal feld of vew and that vares n the depth. Thereby a seres of mages s taken, each from a dfferent angular poston of the camera, by turnng the hybrd sensor system automatcally. By ths procedure a vrtual three-dmensonal test feld s smulated, whch covers the complete horzontal and vertcal feld of vew of the camera. The results n ths paper ponted out, that wthn ths method n hgh accuracy applcatons the nteror orentaton should not be calbrated. But for the eccentrcty estmaton t s suffcent and t mnmze the cost for test feld calbraton on the job. However dependng on the postulated accuracy ths common calbraton could be good enough. It s fast and normally good enough for colorzng 3D pont clouds, for nstance. Because of the hgh correlaton between the eccentrcty and nteror orentaton, both should be always used n common. For hgh accuracy applcatons, the nteror orentaton should be estmated wth multple mage calbraton. Only for the calbraton of the eccentrcty parameters the camera has to be fxed on the scanner. the laser scanner wthn the least-squares adjustment of the system calbraton. REFERENCES AICON, 25. Product nformaton by AICON 3D Systems GmbH. lnk accessed on January 25. Becker, R., Bennng, W., Effkemann, C., 24. 3D- Monoplottng, Kombnerte Auswertung von Laserscannerdaten und photogrammetrschen Aufnahmen. ZFV, 5/24, pp Brown, D. C Close-Range Camera Calbraton. Photogrammetrc Engneerng, 37 (8), pp Calldus, 25. Product nformaton by Calldus GmbH. lnk accessed on January 25. Fraser, Clve S., Dgtal camera self-calbraton. ISPRS Journal of Photogrammetry and Remote Sensng, 52(4), pp Fraser, Clve S., 21. Australs User Manual. Verson 5.5, Unversty of Melbourne. Intel, 25. Open Source Computer Vson Lbrary. lnk accessed January 25. Qvoluton AG, 25. Product nformaton by Qvoluton AG. lnk accessed January 25. Leca, 25. Product nformaton by Leca Geosystems HDS. lnk accessed January 25. Luhmann, Th., 23. Nahberechsphotogrammetre. Second Edton, Herbert Wchmann Verlag, Hedelberg. Maas, H.-G., 1998: En Ansatz zur Selbstkalbrerung von Kameras mt nstabler nnerer Orenterung. Proceedngs of DGPF, Vol. 7, pp.47-53, Munch. Mens, 25. Product nformaton by Mens Corporaton. lnk accessed January 25. Regl, 24. RSCAN PRO Manual. Verson 1.1.1, Regl Laser Measurement Systems. Regl, 25. Product nformaton by Regl LMS GmbH, overvew_/terr_scanner_menu_all.htm, lnk accessed January 25. By further consderaton of parameters n the geometrc mappng functon, possbltes exsts to calbrate or to control