Practical results of GPS/IMU/camera system calibration. Eija Honkavaara*, Risto Ilves**, Juha Jaakkola*

Transcription

1 Practical results f GPS/IMU/camera system calibratin Eija Hnavaara*, Rist Ilves**, Juha Jaala* (*) Finnish Gedetic Institute, FGI (**) Natinal Land Survey f Finland, NLS Keywrds: Bresight, calibratin, interir rientatin, stability. Abstract This article summarizes the results f eleven system calibratins f fur GPS/IMU/tics cmbinatins erfrmed in 22. In additin t the bresight arameters, the interir rientatin arameters aeared t be significant calibratin quantities. In the directin erendicular t the flying directin 2-4 µm systematic errrs were resent with all the tics. With ne f the tics significant fcal length crrectin f 2-4 µm was detected. Stability f bresight and interir rientatin arameters was evaluated. In bresight arameters, the maximum lng-term changes were 2 mgn and the shrt-term changes were less than 6 mgn; 6 mgn differences aeared even between calibratins made during a single day. Changes f the interir rientatin arameters were quite large, but the use f the mst significant crrectins in y and fcal length aeared t be advantageus; the variability f the calibratin scales affected the analysis. The quality f the attitude bservatins was n the range given by the system vendrs. Hwever, ffsets and drifts aeared in the attitude bservatins; these inaccuracies can be ne reasn fr the detected instability f the bresight arameters. In the best blc the recisin f the GPS/IMU sitin bservatins was better than 1 cm; the accuracy analysis f ther blcs was clearly affected by the r quality f the reference bservatins. Small striwise ffsets were detected als in the sitin bservatins. 1. Intrductin The systems fr the direct determinatin f exterir rientatins f airbrne images are becming cmmn. The rientatins are determined by integrating GPS (Glbal Psitining System) and IMU (Inertial Measurement Unit) bservatins made during the maing flight; tw mst significant systems cmmercially available are the Alanix POS/AV 1 DG [7] and IGI AEROcntrl IId [6]. Accrding t the system vendrs the accuracy f the direct sitin bservatins is better than.1 m and the accuracy f the direct attitude bservatins is better than. in ω and φ and better than.8 in κ. Recent emirical investigatins have rved the gd erfrmance f the systems [1, 3]. There exist many rblems hindering the efficient alicatin f the direct gereferencing [2, 4, ]. The requirements f accurate GPS rcessing e.g. clse base statin and gd satellite cnstellatins are nt always easy t fulfil. Several questins fr instance, the stability, the necessary arameters and the efficient calibratin rcedures cncern the calibratin f the systems. Questins als cncern the timal and reliable quality cntrl f the GPS/IMU bservatins; e.g. the thrugh rcedure suggested in [8] can be efficiently alied nly if imlemented rerly t the htgrammetric rcessing envirnment. In the alicatins with quite high quality requirements e.g. better than 2 m gemetric accuracy the accuracy f the datum transfrmatin can be the crucial factr. Results frm ractical tests are needed t finally rve the erfrmance f the systems. Due t the many questins and uncertainties, the general guideline at the mment is t aly the direct gereferencing nly in lw accuracy alicatins, lie in rthht rductin [3]. In the alicatins with higher quality requirements the integrated sensr rientatin shuld be erfrmed. S far the nly extensive results f lng-term stability analysis f the systems have been rerted in [2]. Lng-term stability was evaluated by determining the system calibratin 8 times during almst 2 mnths time erid. The standard deviatins f the bresight arameters f five calibratins were 3.,. and 2.9 mgn fr dω, dφ and dκ, resectively; 3 calibratins were cnsidered as utliers. The authrs cnsidered the stability t be sufficient. Other results f system calibratin are given in [1, 3, 9]; the results have indicated that besides the bresight arameters als at least the camera interir rientatin arameters are necessary calibratin quantities. The bjective f this article is t resent ractical results f GPS/IMU system calibratin. The analysis f 11 calibratin blcs htgrahed in 22 by the Natinal Land Survey f Finland (NLS) ver the calibratin fields f Finnish Gedetic Institute (FGI) using 2 Alanix POSAV TM 1 systems and 4 GPS/IMU/tics cmbinatins are rerted in the fllwing chaters. In Chater 2 the materials and methds are described. The results are given in Chater 3 and discussed in Chater 4.

2 Sjöulla calibratin field, scale 1:4 Sjöulla calibratin field, scales 1:8 and 1:16 Figure 1. Sjöulla calibratin fields: large-scale 1:4 and medium-scale 1:8/1:16. The size f the large-scale calibratin field is 1 m x 1 m and it has 43 GCPs (grund cntrl ints), with 1 cm lanimetric and 2 cm height accuracy, targeted with circular targets with 3 and 4 cm diameter. Size f the medium-scale calibratin field is 4 m x m and it has 12 GCPs, with 1. cm lanimetric and 3 cm height accuracy, targeted with 1 m x 1 m square targets. The calibratin blcs cnsisted f fur arallel flight lines and tw crssing flight lines, with ne arallel and ne crssing flight line flwn twice in site directins. Table 1. Calibratin flights f NLS. The blc structures and the GCP distributins are shwn in Figure 1. Date Blc Otics Plane: Plane: 1326, f= , f= , f= , f= : : :8 1: : : : : : : :16 2. Materials and methds 2.1. Calibratin blcs NLS is erating tw aircrafts, bth having RC2 cameras with exchangeable wide and nrmal angle tics. OH- ACN is Rcwell Turb Cmmander 69A turb twin reller aircraft with a ressurised cabin; is Cessna 41B istn twin reller aircraft with an unressurised cabin. The aircrafts were equied in the sring 22 with Alanix POSAV TM 1 systems with Littn LN-2 IMU. The calibratin tas cnsists f the calibratin f all fur GPS/IMU/tics-cmbinatins. In the emirical investigatin 11 calibratin blcs htgrahed by NLS in summer 22 ver the Sjöulla calibratin fields f FGI were used; the details f the blcs are given in Table 1. The Sjöulla calibratin fields can be used fr large-scale (1:3-1:4) and medium-scale (1:6-1:16) calibratin; the alied blc structures are given in Figure 1. One f the calibratins was made in scale 1:4 in the large-scale calibratin field (blc ), and the rest f the calibratins were made in scales 1:8 and 1:16 in the medium-scale calibratin field. The tics were exchanged between varius calibratins. The GPS base statin was lcated in 3 m distance frm the calibratin field. NLS erfrmed all the rercessing f the data. The GPS/IMU-rcessing was erfrmed with PsPac sftware (V. 4.2). The htgrahs were scanned with 2 µm ixel size by using the LH-Systems DSW scanner. Image measurements were made with LH-Systems ScetSet; tie ints were measured by APM. Preliminary blc adjustments and the eliminatin f the grss errrs were made using the Orima sftware.

3 a) RMSE f AT: sitins (m) b) RMSE f AT: rtatins (mgn) X Y Z Figure 2. Theretical RMSE f reference values estimated in AT: a) sitins and b) rtatins Blc adjustment The calibratins were determined using three different sftware: FGI used FGIAT sftware develed at FGI and inblc sftware f Inh Gmbh (V. 1..); NLS used ORIMA sftware f LH-systems. All the sftware determine the calibratin arameters in a rigrus cmbined adjustment. Adjustments were erfrmed in the lcal tangential crdinate system. At FGI the GPS/IMU bservatins were transfrmed directly frm ECEF t the lcal tangential system; at NLS the bservatins in ECEF were first transfrmed t the Finnish natinal grid crdinate system (j) and rthmetric heights, which were later transfrmed t the lcal tangential crdinates internally in ORIMA. The refractin crrectin was alied t the image bservatins. The ssible unnwns in the GPS/IMU/camera system calibratin were 1. bresight misalignments (dω, dφ, dκ), 2. cnstant GPS/IMU sitin shifts (dx, dy, dz; e.g. caused by wrng initializatin f the ambiguities; either striwise r blcwise), 3. flying directin deendent crrectins a) GPS/IMU sitin errrs (dx, dy, dz; e.g. lever arm r timing difference f the sensrs), b) interir rientatins (x, y, c), 4. ther image defrmatins (e.g. Ebner s arameters, radial and tangential distrtins, affinity) and. glbal datum arameters fr GPS/IMU sitin bservatins (e.g. a full r a artial 7-arameter similarity transfrmatin). Because all f the abve arameters cannt be determined simultaneusly, in the final calibratins the fllwing arameter cmbinatins were used: bresight, crrectins fr interir rientatins, 12 Ebner s arameters (FGI), bresight, crrectins fr interir rientatins, radial distrtin, glbal shift in X and Y directins (NLS) and bresight, datum (7-arameter similarity transfrmatin r glbal ffset), rincial int and Ebner s arameters (FGI). The tw flying directin deendent errrs (3a frm 3b) and height errrs (fcal length crrectin frm dz in 2, 3a and ) culd be searated nly in ne blc flwn in tw scales. In additin the striwise drift arameters were used t mdel the GPS/IMU sitin errrs, but they led t the same bresight arameters as the abve mdels Analysis The analysis cncerned the fllwing items: Quality f direct attitude bservatins. The bserved attitudes were crrected by using the bresight angles estimated fr each blc in the GPS/IMU surted aerial triangulatin (AT). Reference values were btained frm the blc adjustment with GPS/IMU sitin bservatins. The theretical mean errrs (the rt mean square values (RMSE) f the standard deviatins btained frm the inverted nrmal equatin matrix) f the reference attitudes are shwn in Figure 2b; the RMSEs were mgn fr ω and φ and mgn fr κ. The use f the bresight values results in sme crrelatin between the bservatins and the reference values. Nevertheless, it can be assumed that the quality f the reference attitudes is gd enugh fr the evaluatin.

4 Attitude differences, (mgn) Attitude differences, (mgn) Attitude differences, (mgn) Attitude differences, 212 (mgn) Attitude differences, (mgn) Attitude differences, (mgn) Attitude differences, (mgn) Attitude differences, (mgn) Attitude differences, (mgn) Attitude differences, 213 (mgn) Attitude differences, (mgn) Attitude RMSEs (mgn) Figure 3. Differences f attitude bservatins and reference values in mgn (milli gne) fr varius blcs (=ω, =φ, =κ); the stri numbers and images are shwn belw the grahs. The RMSEs are given in the last grah.

5 Quality f direct sitin bservatins. The reference values fr the evaluatin f the GPS/IMU sitin bservatins were btained frm the blc adjustment withut exterir rientatin bservatins. The theretical mean errrs are shwn in Figure 2a. The errr decreases when scale decreases and when the wide-angle tics is used instead f nrmal-angle tics. The errr estimates are als affected by the standard errr f unit weight and the number f tie int bservatins. The accuracy is the best in the blc due t the large scale and the large number f GCPs (.1 m in X and Y,.1 m in Z). The accuracy f Z is always better than.1 m and the accuracy f X and Y is als better than.1 m in the blcs htgrahed by wide-angle tics. In the blcs htgrahed with nrmal-angle tics the recisin f X and Y was m. Bresight and interir rientatin arameters: evaluatin f the imrtance and standard deviatins f the arameters and cmarisn f results f varius sftware (FGIAT, InBlc, Orima). Evaluatin f the stability f the bresight and interir rientatin arameters. Differences f the varius calibratins were calculated and grued based n the time differences between the calibratins (within 1 day, 2 days, 4 mnths, 2 mnths). Alteratin within -2 days time erid indicates shrt-term stability and the changes ccurred within 2 and 4 mnths time erid reresent lng-term stability. Accuracy f the direct gereferencing. Quality f direct gereferencing was evaluated by bac-rjecting the GCP grund bservatins t the images by using the direct exterir rientatin bservatins, and then cmaring the calculated values t the measured values. The fllwing crrectins were alied: a) the bresight crrectin estimated fr the blc, b) the interir rientatin, datum and bresight crrectins estimated fr the blc and c) interir rientatin and bresight crrectins estimated frm the first calibratin f the tics. In tw first cases the same GCPs were used in the determinatin f the arameters and in the quality cntrl, which shuld be taen int accunt in the evaluatin f the results. 3. Results 3.1. Quality f GPS/IMU attitude bservatins The differences f the bserved and the reference attitudes and their RMSEs are shwn in Figure 3. The RMSEs were in accrdance with the vendrs secificatins, excluding ω and φ f blc and ω f blc 212. There aeared a data ga in the IMU bservatins in the beginning f the flight, which culd be the reasn fr the r results f the blc. The average RMSEs were 4, 3 and 4 mgn fr ω, φ and κ, resectively. The differences given in Figure 3 indicate ffsets between stris and linear drifts; similar henmena were als aarent in the residuals after the calibratin calculatins. Drifts are esecially significant in the blc, and drifts can be detected in mst f the blcs esecially in φ and κ bservatins. Quite large ffsets (>1 mgn) between stris are resent, fr instance, in the blcs and, and smaller ffsets can be detected in mst f the blcs. The mst feasible exlanatin fr these errrs is inaccuracy f the GPS/IMU rcessing Quality f GPS/IMU sitin bservatins The analysis f the GPS/IMU sitin bservatins indicated bth glbal datum errrs and systematic flying directin deendent errrs. The flying directin deendent errrs are analysed in Chater 3.4. The estimated glbal shift arameters are shwn in Figure 4; the sitin shifts are tyically abut.1 m and they are at least artially caused by sme datum difference between the GCPs and the direct sitin bservatins. The large height shifts f tics 7183 are caused by an errr in the fcal length. RMSEs f the riginal GPS/IMU sitin bservatins are shwn in Figure a. RMSEs were quite large; the maximum values were abut.6 m. The Z accuracy was.-.18 m, excluding the tics 7183 having large height crrectins. The main reasn fr the r accuracies in X and Y was the systematic flying directin deendent errr.

6 Glbal ffset f GPS/IMU sitins (m) Figure 4. Glbal ffset arameters estimated fr the GPS/IMU sitin bservatins. a) RMSE f riginal GPS/IMU sitins (m).6 X..4 Y.3 Z b) RMSE f crrected GPS/IMU sitins (m) X Y Z dx dy dz Figure. a) Accuracy f riginal GPS/IMU sitins and b) accuracy f the crrected (datum, flying directin deendent errr) GPS/IMU sitins. The systematic errrs (flying directin deendent errr and datum) were determined fr each blc and eliminated frm the GPS/IMU sitin bservatins. The results f the cmarisn f the crrected bservatins and the reference values are shwn in Figure b. After the crrectins the RMSEs were. m.3 m in X and Y and abut.1 m r less in Z. The accuracy f X and Y bservatins was in mst f the cases wrse than culd be exected, but resumably the r quality f the reference bservatins had influence n the results. The effect f scale can be detected by cmaring tw cases with blcs flwn in the same day (blcs and and blcs and 212). In bth cases the accuracy is better in the larger scale, which indicates the better accuracy f reference values. The best results were btained with the blc, which is a 1:4 scale blc htgrahed using the wide-angle tics. The RMSEs were befre the crrectins.1 m,.6 m and.4 m (X, Y and Z) and after the crrectins less than.4 m in all three crdinates. The blcs with scales 1:4 and 1:8 were analysed further. The differences f the crrected sitin bservatins (flying directin deendent errr and datum) and the reference values are shwn in Figure 6; the RMSEs are given in the last grah (the first and the last images f each stri are nt included in RMSEs). In the Persective centre sitin differences (m), 212 (tics 7183, c=21 mm) X Y Z Persective centre sitin differences (m), (tics 7183, c=21 mm) X Y Z Persective centre sitin differences (m), (tics 1313, c=1 mm) X Y Z Persective centre sitin differences (m), (tics 1313, c=1 mm) X Y Z Persective centre sitin differences (m), (tics 1326, c=1 mm) X Y Z Psitin RMSEs rmse X rmse Y rmse Z 212 Figure 6. Differences between crrected GPS/IMU sitin bservatins (flying directin deendent errr, datum) and reference values fr 1:4 and 1:8 scale calibratin blcs; stri numbers and images are shwn belw the grahs. RMS values f differences are shwn in the last grah; the first and the last images f the stris are nt included t the RMSE calculatin.

7 d d d Bresight arameters (mgn) 212 _ Bresight standard deviatins (mgn) sd_d sd_d sd_d 212 _ Figure 7. Bresight arameters and estimated standard deviatins given by FGIAT sftware. Interir rientatin arameters (micrmeters) c y x Interir rientatin standard deviatins (micrmeters) sd_c sd_x sd_y 212 _ _ Figure 8. Crrectins fr interir rientatin arameters and estimated standard deviatins given by FGIAT sftware. blc (scale 1:4, large-scale calibratin) the differences were mstly belw.1 m; with the ther blcs the maximum differences were in general.3-. m in X and Y and less than.2 m in Z. Striwise shifts and drifts culd be detected frm the difference lts; these can arise frm the systematic errrs f the reference values and frm the GPS/IMU sitin bservatins. Striwise ffsets were evaluated by blc adjustment after alying the flying directin errr and datum crrectins t the sitin bservatins. Offsets were in general less than.1 m; maximal ffsets f.1-.2 m aeared in blcs,, and, in blc 213 aeared a.3 m ffset in ne stri Brsight arameters Bresight arameters and their recisins, given by the FGIAT sftware, are shwn in Figure 7. The estimated standard deviatins are in average.8 mgn in dω and dφ and 1.2 mgn in dκ. The analysis f the residuals f attitude bservatins after the adjustment revealed similar striwise ffsets and drifts as the quality analysis f attitude bservatin in Chater Interir rientatin arameters Crrectins fr the interir rientatin arameters and their standard deviatins, given by the FGIAT sftware, are shwn in Figure 8. It shuld be nticed that these crrectins mdel the systematic errrs f bth interir rientatins and sitin bservatins (Chater 2.2). It can be seen that there was a significant crrectin f size 2 4 µm in directin erendicular t the flying directin with every tics (y). With tics 7183 there was a significant crrectin in height (2-43 µm); with the ther tics the height crrectin was mstly less than µm. Based n the analysis and the NLS exeriences, the majr reasn fr these crrectins is the change f the interir rientatin in the flying cnditins.

8 a) Stability f bresight arameters (mgn) b) Stability f interir rientatin arameters (micrmeters) d d d c x y days 2 days 4 mnths days 2 days 4 mnths Figure 9. Stability f tics 7183: a) bresight arameters and b) interir rientatin arameters. 3.. Stability The different scales f the calibratin blcs affected esecially the analysis f interir rientatin, because f the scale deendent henmena (redminantly different hysical cnditins in different flying altitudes and the systematic GPS/IMU sitin errrs having different effect in different scales). Stability f the bresight arameters f tics 7183 is shwn in Figure 9a. A general finding was that the changes were the largest in dω and usually the smallest in dφ. Differences f the varius calibratins were less than 6 mgn; 6 mgn differences aeared even between the calibratins f blcs and 212 htgrahed cnsecutively. The shrt-term results f the ther tics were similar. In lnger time intervals larger changes ccurred with the ther tics; e.g. in the tw tics f almst 2 mgn change in dω did tae lace during the summer (Figure 7a). One exlanatin t the shrt-term instability is the detected striwise ffsets and drifts f attitude bservatins. One reasn fr the lng-term instabilities was undubtedly the exchanges f the tics. Results f the stability analysis f interir rientatin arameters f the blc 7183 are shwn in Figure 9b. The mst reresentative results are the cmarisns between blcs and 212 and between blcs and, having the same scales. The differences f the blcs and were the largest, rising u t 1 µm in y. The differences were abut µm r less between blcs and 212. Frm Figure 8 it can be seen that even thugh the varius slutins are quite different, the use f the imrved values fr c in tics 7183 and fr y in all the tics wuld be advantageus in direct gereferencing Cmbined calibratin f tw scales Table 2. Lever arm and interir rientatin crrectins btained frm the cmbined adjustment f tw scales. Sftware Parameter Value Standard deviatin FGIAT Lever arm dx dy dz dx dy dz (m) Interir rientatin x y c x y c (µm) The blcs (scale 1:16) and 212 (scale 1:8) were adjusted simultaneusly in a single adjustment in rder t searate interir rientatin crrectins frm the flying directin deendent and height crrectins f GPS/IMU bservatins. The arameters given by FGIAT sftware are shwn in Table 2. Effect f scale was already aarent in Figure 8 in the fcal length crrectin; the crrectin fr the GPS/IMU heights resulted in different effect in tw scales. The results address that the interir rientatin is the majr surce f the flying directin deendent and height errrs. The analysis f the crrelatins in the cmbined adjustments made by NLS revealed crrelatins in the height arameters (ersective centre, fcal length, glbal dz), thus the arameters are nt rbably cmletely reliable. In the lever arm estimatin f the PsPac sftware the estimated lever arms have been a few centimetres, thus the lever arm arameters, estimated by FGIAT, are slightly larger than the PsPac estimates Differences f varius sftware The arameters btained frm three different sftware were cmared. The calculatin f FGIAT and inblc were made using the same arameters (bresight, interir rientatin, Ebner s arameters), weighting and bject

9 Table 3. Differences f bresight and interir rientatin arameters btained by three different sftware (RMSE and maximum differences f 11 calibratin blcs). Calibratin arameters were in FGIAT and inblc bresight, interir rientatin and Ebner s arameters and in Orima bresight, interir rientatin, radial distrtin and glbal X and Y shifts. Cmarisn Bresight arameters Interir rientatin arameters RMSE (mgn (mgn) RMSE (µm) (µm) dω dφ dκ dω dφ dκ dc dx dy dc dx dy FGIAT-Inblc FGIAT-Orima crdinates, thus the ssible differences shuld result in frm differences in mdelling. The rcessing in Orima was quite different: arameters were bresight, interir rientatin, radial distrtin and glbal shift in X and Y directins, the weighting were different and the bject crdinate system was different. Differences f the bresight and interir rientatin arameters given by three different sftware are shwn in Table 3. FGIAT and inblc gave very similar results; in bresight arameters the maximum differences were.71 mgn and the RMSEs were less than.3 mgn; in interir rientatin arameters the maximum differences were less than 3. µm and the RMSEs were less than 1.6 µm. The arameters given by Orima sftware varied mre frm the results f FGIAT and inblc; the majr reasns fr the big differences were the different crdinate systems and the different mdels. The differences between Orima and the ther sftware were systematic, thus the cnclusins f stability and erfrmance were similar in all the systems Accuracy f direct gereferencing The results f the evaluatin f the direct gereferencing accuracy (RMSE) are given in Figure 1. In the first case, where nly the bresight crrectin was alied (Figure 1a), the errr in the directin erendicular t the flying directin was evident (Chater 3.4); the accuracy f DG was 1-1 µm in x and 22-4 µm in y. When the systematic errrs (lever arm and datum) were eliminated frm the sitin bservatins, the accuracy imrved t 8-1 µm in x and 1-2 µm in y (Figure 1b). In many cases the accuracy f y was wrse than the accuracy f x. One ssible exlanatin fr this culd be the ssible rer recisin f ω-bservatins. The accuracy f the blc was the rest, which was rbably due t the weaest accuracy f the rtatins (Figure 3). In the last case (Figure 1c) the bresight and interir rientatin arameters were estimated frm the first calibratin blc f each tics (,, and ). The change f dω in was evident in the results; dx is 3-4 µm and dy is -6 µm. In the ther blcs dx is µm and dy is 2-3 µm. The results are wrse than in Figure 1b due t the instability f the arameters. 4. Discussin a) DG accuracy in image (micrmeters), riginal sitin bservatins dx dy b) DG accuracy in image (micrmeters), datum and lever arm crrectins In the revius sectins results f the GPS/IMU/camera system calibratin f fur GPS/IMU/tics cmbinatins were given. A remarable finding was the large 2 t 4 µm in image crrectin in the directin erendicular t the flying directin (y). Fr ne tics the crrectin fr the fcal length was 2-4 µm; fr the ther tics the crrectin was mstly less than µm. The crrectin in the flying directin aeared t be abut -1 µm. On the basis f the abve analysis and the revius exeriences f NLS, the crrectins in y and c are caused mainly by the changes f interir rientatin f the camera in the flying cnditins. Similar findings have been made earlier in [1, 3, 9]. dx dy c) DG accuracy in image (micrmeters), calibratin values f the first calibratin Figure 1. Accuracy f bacrjectin f the GCPs (RMSE). Crrectins alied: a) bresight crrectin estimated fr the blc, b) interir rientatin, datum and bresight crrectins estimated fr the blc and c) bresight and interir rientatin crrectins estimated fr the first calibratin flight f each tics. dx dy

10 Stability f the calibratin arameters was analysed. The bresight arameters varied 6 mgn even in the flights flwn successively; the maximum changes f the lng-term calibratin were abut 2 mgn. Pssible exlanatin fr the big changes is the exchanges f the wide and nrmal angle tics between the calibratins. The detected shifts and drifts resulted in instability esecially t the shrt-term stability analysis; the imrvement f the GPS/IMU integratin methds will hefully decrease these henmena. The stability analysis f the interir rientatin arameters was difficult because the flights were made in different scales. Hwever, the use f detected significant crrectins fr y and c aeared t be rfitable. The quality f the attitude bservatins was n the level secified by the system vendrs; the average RMSE was abut 4 mgn. This indicates, hwever, nly the internal recisin, because the bresight arameters were estimated fr each flight. Instability f the bresight arameters will deterirate the direct attitude bservatins in ractise. The analysis revealed shifts and drifts in the GPS/IMU attitude bservatins; similar findings were rerted in [2]. The quality f the reference bservatins in the evaluatin f the sitin bservatins was cmletely sufficient nly in ne blc; the RMS accuracy was better than.1 m. The determined height accuracy was better than.1 m in many cases. Small striwise ffsets were detected als in the sitin bservatins; the maximum crrectins varied frm less than.1 m t abut.3 m. This investigatin will cntinue with a cmlete analysis f the stability. It is essential that the system users systematically gather infrmatin f the systems in ractical wr in rder t mae cnclusins f the erfrmance f the varius systems; in this investigatin all the fur GPS/IMU/tics-system cmbinatins aeared t have differences in their behaviur. The stability aeared t be the weaest int f the analysis; in the future the stability can be imrved alng the develment f the rcedures and GPS/IMU-integratin methds. Acnwledgements Eer Ahas frm FGI is gratefully acnwledged fr carefully building and maintaining the Sjöulla calibratin fields used in this wr. Bibligrafía [1] Cramer, M., 21. Perfrmance f GPS/Inertial Slutins in Phtgrammetry. In: Fritsch/Siller (eds.): Phtgrammetric Wee 21, Wichmann Verlag, Heidelberg, Germany, [2] Cramer, M, Stallman, D., 22. System Calibratin fr Direct Gereferencing. In: Internatinal Archives f the Phtgrammetry, Remte Sensing and Satial Infrmatin Sciences. Vl. 34, Part 3A [3] Heie, C., Jacbsen, K., Wegmann, H., 22. Analysis f the Results f the OEEPE Test Integrated Sensr Orientatin. In: Heie, C., Jacbsen, K., Wegmann, H. (eds.): Integrated Sensr Orientatin, Test Rert and Wrsh Prceedings. OEEPE Official Publicatin N [4] Himle, S., 21. Sensr integratin and data fusin in raxis. In: Fritsch/Siller (eds.): Phtgrammetric Wee 21, Wichmann Verlag, Heidelberg, Germany, [] Jacbsen, K., H. Wegmann, 21. Deendencies and rblems f Direct Sensr Orientatin. Integrated Sensr Orientatin. OEEPE Wrsh Set , 21 Hannver, Germany. IPI, Hannver 21. [6] Kremer, J., 21. CCNS and AEROcntrl: Prducts fr Efficient Phtgrammetric Data Cllectin. In: Fritsch/Siller (eds.), Phtgrammetric Wee 21, Wichmann Verlag, Heidelberg, Germany, [7] Mstafa, M., Huttn, J., B. Reid, 21. GPS/IMU rducts the Alanix arach. In: Fritsch/Siller (eds.): Phtgrammetric Wee 21, Wichmann Verlag, Heidelberg, Germany, [8] Mstafa, M. M. R, 22. Quality Cntrl f Direct Gereferencing Data. In: Prceedings f ISPRS Cmmissin I Mid-term Symsium, Nvember 1 t 1, 22 : Denver, Clrad, USA. [9] Wegmann, H., 22. Image Orientatin by Cmbined (A)AT with GPS and IMU. In: Prceedings f ISPRS Cmmissin I Mid-term Symsium, Nvember, 22 : Denver, Clrad, USA.