SYSTEM CALIBRATION OF LAND-BAED MOBILE MAPPING SYSTEMS

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1 SYSTEM CALIBATION OF LAND-BAED MOBILE MAPPING SYSTEMS By Ther Hssn nd Nser E-Shemy Moe Mut-sensor eserh Group Deprtment of Geomts Engneerng, The Unversty of Cgry 5 Unversty Dr. N.W. Cgry, Aert, Cnd TN N4 Te: (43) 7587, Fx: (43) E-m: tfs@ugry., nser@geomts.ugry. KEY WODS: Moe Mppng, Photogrmmetry, Boresght Crton, unde Adjustment. ABSTACT: The nresng demnd for up-to-dte 3-D geogrph nformton systems (GIS) dt for pnnng, trnsportton, nd utty mngement pptons poses sgnfnt henges to the Geomts ommunty. Of the henges n qurng, udng, mntnng, nd usng GIS, none s more entr thn tht of dt quston. Otnng the requred spt nd ttrute dt y onventon methods suh s er photogrmmetry nd terrestr surveyng s expensve nd tme onsumng. These methods re, therefore, not we suted for rpd updtng of GIS dtses. Fortuntey, the deveopment of nd-sed moe mppng systems (MMS) hs opened new venue to meet these henges. Lnd-sed MMS re pe of provdng fst, effent, ost-effetve nd ompete dt quston systems. As suh, they re n nnovtve tehnoogy for retng nd updtng 3-D GIS dtses oth quky nd nexpensvey. The devered ury of MMS s funton of sever prmeters. Ths nudes the ury of the nvgton omponent whh provdes the soute oton nd orentton of the system. Indvdu sensor rton provdes modes for orretng ther mesurements systemt errors. Tot system rton s key ftor n MMS performne. In ths step, the geometr retonshp etween the mppng sensor nd the nvgton sensor s estmted. Ths nvoves the determnton of the mer perspetve entre oton wth respet to the Inert Nvgton Systems (INS) trd entre whh s typy prt of the nvgton omponent. Aso, the rotton nges etween the mer xes nd the INS xes re estmted. In ths pper, we report our experene n rtng the VISAT TM (Vdeo-Inert-SATete) moe mppng system whh s deveoped y Asoute Mppng Souton In. The pper presents the dfferent terntves n oresght rton. A projet reenty fnshed n Cgry, Cnd, provded the opportunty to test the system under dfferent fed ondtons. esuts of these tests re reported n ths pper wth more emphss on the mpt of system rton on the soute nd retve ury of the VISAT system.. INTODUCTION Moe mppng systems (MMS) provde ompete mppng souton wth dt qured from ony one ptform. The de of moe mppng hs een round for t est s ong s photogrmmetry hs een prted. The ery deveopment of moe mppng systems ws, however restrted to pptons tht permtted the determnton of the eements of exteror orentton from exstng ground ontro. However, tehnoog dvnement n postonng/nvgton nd mgng sensors sustnty refned the onept of rorne nd nd-sed mppng. The dvent of the frst moe mppng system n the ery 99s ntted the proess of estshng modern, fuy dgt, vrtuy ground ontro-free photogrmmetry nd mppng, whh onsdery enhned oth the effeny, the fexty nd the ost (fter Shwrz nd E-Shemy, 4). The rton of MMS s n essent step pror to usng the system n operton envronment. It n e dvded nto two prts: rton of eh ndvdu sensor nd tot system rton (.e. rton of the spt reton etween dfferent sensors). Cmer rton nudes the estmton of the mer prnpe dstne, the shft of the prnpe pont, nd the ens dstorton prmeters, whh usuy refereed to s ntern orentton prmeters. Inert Nvgton Systems (INS) re sujeted to dfferent rton tests to estmte ther sensors systemt errors (e.g. ses, temperture senstvty, nd se ftors). VISAT ws mong the erest MMS deveoped t the deprtment of Geomts, Unversty of Cgry n ery 99 s. eenty nd newer verson of the VISAT TM hs een deveoped y Asoute Mppng Souton In. In ths pper we report the tsk of rtng oresght prmeters of the tthed mers. The mn fous w e on the nter-sensor rton. Pre-rton preprtons re dsussed. Cmer nd system rton proedures re ustrted wth emphss on prt mpementton spets. Dfferent proessng senros re tested nd ommented. Fny, onusons re drwn.. PECALIBATION POCESS System rton proedures nvove the estmton of the spt retonshp etween mppng sensor (e.g. mer) nd the nvgton sensor (.e. INS/DGPS). Ths retonshp n e sudvded nto ner nd ngur offsets. The ner offset n e mesured usng trdton surveyng methods y tot stton or stee tpes. Whe the estmton of msgnment nges etween the mer nd the INS s done y omprng the INS rotton mtrx m (etween the INS ody frme

2 nd the mppng frme m ) wth ndependent m (etween the mer frme nd the mppng frme m ) s n er trnguton output (Wegmnn nd et.., 4). More rgorousy, tot system rton n e performed smutneousy usng unde djustment proedures, whh estmtes oth ner nd ngur offsets (e.g. Ystk 4) s we s ther ury estmtes. The ter tehnque hs een pped. In pprohes, t s requred to estsh n urte, rh, nd we dstruted ontro fed, smr to Fgure. Ths s usuy done usng terrestr surveyng tehnques. Hgh preson surveyng tehnques nd nstruments re used, whh yed to ury n the mmetre eve or even etter. Te Pont Fgure : Contro Fed for VISAT MMS System Crton Contro fed must e omputed n the sme oordnte frme of the INS/DGPS output. Forty-sx (46) ontro ponts hve een estshed n ddton to 4 te ponts were temporry fxed durng the rton sesson to enhne the geometry. It goes wthout syng tht the ontro ponts must e spty we dstruted to enhne the mode geometry nd onsequenty ts photogrmmetr souton ury. The estshed sene, for photogrmmetr trget surveyng, must e ouped y GPS reevers f posse dependng on GPS sgn vty. It s not wys posse to oupy sene ponts when ontro ponts re estshed ner retvey t udng to get good nterseton geometry. In suh se, nother se ne n open sky must e fxed. Lter on, terrestr network shoud e run to onnet senes whh n foow the trdton ontro network herrhy (.e. tretrton, trnguton, hyrd, or trverse). Hyrd networks re preferred for hgher degree of freedom nd etter ury. Network djustment resuts shows tht the stndrd devton of the ontro ponts s round mm. Contro network djustment n e done n one of the foowng frmes: - Erth Fxed Coordnte Frme (EFCF) - Unvers Trnsverse Mertor (UTM) Independent mer rton hs een performed y the dgt photogrmmetry reserh group (DPP) t the Unversty of Cgry, sed on unde djustment wth sef rton usng oth pont nd ner fetures. Lortory mer rton hs een undertken n ontroed envronment. For ompete desrpton of the method used, the reder n refer to H et.., ; H nd Morgn, 3 nd 4. They so nvestgted mer stty ssues. Two sets of rton prmeters re ve (Two dys) wth the onuson tht the mers re fry ste. Durng our proessng, ony one prmeter set ws onsdered due to mer stty. It s not good prtse to tke verge of the two dt sets. One n seet one rton set s they re equvent nd w yed to the sme ojet spe oordntes. The used mthemt mode for rd ens dstorton pped n mer rton s gven n equton xld = x[ K( ) + K( ) (. LD = y K + K xld = x[ K( ) + K( ) ( LD = y K + K Where r = x x ) + ( y y ), nd r o s n rtrry vue ( p p tken s mm. K, K nd K3 re the rd ens dstorton prmeters, xp nd yp re the mge oordntes of the prnp pont, x nd y re the mge oordntes of the mesured pont. The term K one w usuy suffe n medum ury pptons. The nuson of the K nd K3 terms mght e requred for hgher ury nd wde-nge enses. Hene VISAT mers hs snge ens, de-entr ens dstorton ws not ppe. Cmer CCDs re squre nd thus ffne dstortons re negeted. Ths mode s med to hve muh omputton stty nd ess nose dependeny. Ths mode s dfferent from the mode used n system rton softwre n whh r o =. Ths mkes the K output s not drety ompre. The motvton ehnd performng ndvdu mer rton nd not estmtng mer ntern orentton prmeters (IOPs) durng oresght rton ws due to the exstene of sgnfnt orreton etween the oresght nd the mer IOP (Hepke, et. A., ). Ths mkes the estmton of oth prmeters sets n one sesson s suspeted. Both senros were tested. In gener, t s dvse to perform mer rton pror to system rton, ssumng tht the mers re ste nd the mountng proess w not ter the mer IOPs. Moreover, mer IOPs mght hnge under tu test ondtons (Meer, 978). 3. MATHEMATICAL MODEL Equton f f f r = t + t ro ( ) ( ) λ r s the s mthemt mode for the mppng proess of MMS ether eng er or nd-sed. It s smpe nd sed on smpe vetor summton. f f f r = t + t ro ( ) ( ) λ r Where f r s the 3-D oordnte vetor of pont () n the omputton frme (f-frme) f r o (t) s the nterpoted oordnte vetor of the nvgton sensors (INS/DGPS) n the f-frme λ s the se ftor orrespondng to pont () (t) s the nterpoted rotton mtrx etween the mer f frme (-frme) nd the f-frme

3 (t) r s the tme of mge pture s the orreted mge oordnte mesurement vetor s the vetor from the mer to the ody frme, mesured n the -frme e-wrtng the prevous vetor form n mtrx form, one gets the foowng system of equtons. IMU r X Xo x f f Y = Yo + λ y 3 Z Zo f p The rotton mtrx f n e further nyzed dependng on the omputton frme (ether o eve frme [] or erth fxed oordnte frme [e]) nto: f e = 4 The rotton mtrx n e omputed sed on ro, pth zmuth prmeterzton (usuy used n nvgton) s foows: = ( r) ( p) 3 ( ) 5 Where r, p, nd re system ro, pth, nd zmuth respetvey. [,, nd 3] re rotton out x, y, nd z respetvey. Addtony the oresght rotton mtrx n e omputed s = ( r) ( p) 3( ) 6. Fgure : eton etween Nvgton nd Mppng Sensors As mentoned erer, the ury of moe mppng depends on the ury of nvgton souton, mer/system rton, mge mesurement nose, nd tme synhronzton etween dt strems. To understnd the error udget, ponts were smuted 5-5 m wy from mers. Errors re smuted eh for ury governng eement. Fgure 3 summrzes the ntrodued error to eh eement nd ts orrespondng perentge effet on the MS on the 3D mppng ury. It s er tht some errors hve nsgnfnt effet (e.g. system ro, mer ro, nd ens dstorton) nd some others hve mjor ontruton (e.g. system poston, se ength n x dreton, nd shft of the prnpe pont n x dreton) on the mppng ury. Both system synhronzton nd mge mesurement nose were not nuded. The tot MS 3D mppng ury wth ntrodued errors s 35m. = ( r) ( p) 3( ) 6 Where: = r, p, re oresght nges, see Fgure. mtrx s sed on oordnte system defnton of oth ody frme (x-rght, y- forwrd, z-up) nd mer frme (x gned wth mge rowsrght, y gned wth mge oumn-up, z ompetes rght hnded oordnte system). Fny: r r r3 = f r r r3 7 r 3 r3 r33 The orrespondng onerty ondtons, whh nudes the system rton prmeters enng ther estmton wthn unde djustment frmework: r X X r Y Y r Z Z x f o + o + o + = ( ) 3( ) r3 ( X Xo) + r3 ( Y Yo ) + r33 ( Z Zo) + r ( X X r Y Y r Z Z y f o) + ( o) + ( o) + = 3 r3 ( X Xo) + r3 ( Y Yo ) + r33 ( Z Zo) + 8 Fgure 3: Error Contruton to Mppng Aury 4. CALIBATION SESSION Before performng the experment, the rton sesson hs een refuy desgned sed on the extenson of the ontro fed, mers dstruton, nd mer fed of vew. The go of suh desgn s to hve the ontro ponts we dstruted wthn the mge spe. Nne (9) system postons hve een desgned nd ssgned oordntes wth respet to fçde o oordnte system s shown n fgure Fgure 4. At the tme of the rton, the vn ws rought to the pre-desgned otons mrked on the ground.

4 X 4 [4, ] Fçde ~m [9, 7.5] [, 4] 3 Fçde The INS tttudes re used wthout ny orreton. EFCF ws dopted s djustment fme for our omputtons. One the djustment hs onverged, the resuts n e then trnsformed k to the mppng frme for etter understndng of the resuts. - Unvers Trnsverse Mertor (UTM) The djustment n e so done n the UTM projeted oordntes. The INS zmuth s wth respet to the o (north) merdn where the system ws gned (nt gnment) whe ontro network s gned wth zone entr merdn. Therefore, INS zmuths must e orreted due to onvergene of merdns. The omputton of the onvergene of merdns n e n e found n Borre (we ste) nd Nssr 994. eferene Pont [X, Y] Y Ths orreton s sever (up to 3 ) t the zone order nd hgh ttudes. In Cgry, the ttude s 5 nd the Longtude s round (-4 ). The zone entr merdn s -7 (UTM zone numer ). Therefore the merdn onvergene s Setup No Some Addton Temporry Te Ponts Fgure 4: Exmpe of the Exeuted Vn Postons To otn the est system rton ury, enhned nvgton souton must e ve. If the GPS sgn re oked (e.g. ostruted y surroundng udng), the INS w e workng s stnd one nd the ury of nvgton souton w e degrded sne no extern dng s ve. To overome ths proem, prsm ws fxed t known ever rm to the INS entre. At eh vn oton, the prsm oordntes were surveyed from fxed se stton usng tot stton. The strt nd end tme of eh vn oton were reorded. The surveyed postons ts s oordnte updte whh were proessed together wth the INS sgn, usng the Unversty of Cgry s AINS softwre, n Aded Inert Nvgton System Tooox for MtL (Shn nd E-Shemy 4) fter ppyng Non-Hoonom Constrnts (NHCs), kwrd fterng/smoothng nd Odometer Derved-Veotes (ODV) s updte mesurements. System poston nd tttude re nterpoted t the mge exposure tmes n eh vn oton. 5. COMPUTATION FAMES Smr to the ontro network djustment, the rton n e done n one of the foowng frmes: - Erth Fxed Coordnte Frme (EFCF) In ths se the oordntes re trnsformed to EFCF nd the tttudes re mutped y the rotton mtrx etween the o eve frme nd the EFCF. The o eve frme s defned s X = Estng, Y=Northng, nd Z = Up. e = 3( 9 λ). ( ϕ 9) sn λ snϕ osλ osϕ osλ e = osλ snϕ sn λ osϕ sn λ 9 osϕ snϕ Where φ nd λ represent the geogrph oordntes of the system s defned y the INS enter. Lttude Longtude Dfferene From Centr Merdn Fgure 5 shows onvergene of merdn ontour nes for qurter of UTM zone (symmetr n oth dretons). It must e stressed out here tht the unde djustment s not senstve to zmuth systemt error. Ony rndom error w e vse n the stndrd devton of the estmted prmeters. Systemt error w e toty sored y the estmted prmeters yedng wrong rton set. Lttude Longtude Dfferene From Centr Merdn Fgure 5: Convergene of Merdn ontour Lnes Usefu remrks on orreton neessry when usng UTM s n djustment frme of rorne MMS n e found n (Josen, 3). egrdess the dopted djustment frme, the foowng dt eements re nvoved n the djustment: Cmers rton prmeters.

5 Approxmte vue for oresght nges from desgn. Interpoted system postons. Interpoted system tttudes. Imge mesurements Contro ponts oordntes Durng the 3D omputton n the UTM oordnte frme, the INS zmuth must e orreted for the merdn onvergene ( α) s foows: Correted zmuth = INS zmuth - α Fgure 6 shows mers dstruton n one of the enosures of VISAT TM. The mers re Kodk KAI- mer. The mer hs 6 pxe CCD rry, nd pxe sze of 7.4 mrons. The mer fo ength s 7 mrons. The se dstne etween the two mer enosures s.5 metres. Fgure 6: VISAT Imgng System (Left Enosure) Moton Dreton (III), estmtes the K vue n ddton to system rton prmeters. In ses, mge mesurements hve to e orreted from dfferent knds of dstortons efore usng them n the 3D omputton. The mppng ury of senros (II, IV, V) ws reomputed sed on the dstorton mode n x equton LD = x K + K LD = y K + K wth ro =. (.e. the sme s n system rton). Ths ws done to hek f the two dstorton modes (ro =. or ro=. mm) w yed to the sme ury. 7. ESULTS Te sts the sttsts for the dfferent tested senros for prx, estng, northng, eevton, D, nd 3D. Men, mxmum, mnmum, nd MS re omputed. Among the dfferent tested senros, senro I, where the IOPs were estmted n ddton to the estmted oresght prmeters, yeded the most urte resuts. The mprovement s not sgnfnt. However, ths ws surprsng ut my e due to the numer nd the geometry of oth vn nd ontro ponts whh strengthened the photogrmmetr network nd redued the orreton etween the dfferent groups of estmted prmeters. Ths senro hs the dvntge over performng pror mer rton s ths vods mer nstty due to mountng proess nd the estmton s under fed ondtons. 6. EXPEIMENTS The mn ojetve of ths pper s to otn system rton prmeters whh yed to the optmum mppng ury. Fve proessng senros hve een tested. To hek the ury of eh rton set, n ndependent hek sed on estshed ground ontro ponts were used. Twenty () Ground ontro ponts hve een estshed usng DGPS. Mnhoes, rn gutters, rod sgns, nd ne ne mrkng were hosen s ontro ponts nd were eh ouped y GPS reever for 3 mnutes stt survey. These ponts must e heked f they pper n t est two mges. Imge mesurements for ontro ponts were mesured, usng the VISAT TM stton usng the two front mers ony (B n Fgure 6). For eh senro, the 3D oordntes s we s the orrespondng prx were omputed usng forwrd nterseton. The MS of the dfferenes etween the 3D oordntes, omputed sed on spef system rton senro, nd ther orrespondng referene vue from DGPS survey were omputed for estng, northng, eevton, D, nd 3D. The frst senro estmtes oth oresght nd mer nteror orentton prmeters (IOP) whh ssumes no pror mer rton hs een performed. As mentoned efore, mer rton used dfferent rd dstorton mode from those used n equton xld = x[ K( ) + K( ) (. LD = y K + K Therefore, K vue n not e ntrodued s fxed vue. To do smr effet, mge mesurements were orreted sed on k vue nd the orrespondng mth mode s senro II, nmed s dstorton free senro. Usng the orreted mge mesurements, two senros were tested n whh the fo ength nd the prnpe pont (PP) shft were estmted respetvey (senros IV, nd V respetvey). Lst senro ALL IOP (I) Dstorton Free (II) K (III) Fo ength (IV) PP. Shft (V) Men Mx. Mn. MS P.... E N H D D P..3.. E N H D D P..3.. E N H D D P..3.. E N H D D P..3.. E N H D D

6 Te : Mppng Aury Sttsts for Dfferent Proessng Senros. Comprng the resuts of dfferent tests, t n e so onuded tht our estmton of prmeters re very ste though the estmton of prmeters from dfferent senros yeded dfferent vues for the sme prmeter. The mxmum dfferene etween dfferent senros s sted n Te. Cmer Boresght Cmer IOPs Item Mx. Dfferene X mm Y m Z 3mm o Pth Azmuth 3 Fo ength 3pxes PP shft x pxe PP shft y pxe Te : Dfferene n Estmton wth Dfferent Proessng Senros Chnge n one prmeter my e sored y nother prmeter yedng to the sme ojet spe. It ws neessry to test f the resuts from the two rd dstorton modes (ro =. or ro=. mm) re equvent. After estmtng the oresght prmeters from senros II, IV, nd V, the mppng ury ws reheked wth the other dstorton mode. It ws oserved tht the two modes yeded to most dent resuts. Te 3 shows suh resuts. Dstorton Free (II) Fo ength (IV) PP. Shft (V) Men Mx. Mn. MS P..3.. E N H D D P..3.. E N H D D P..3.. E N H D D Te 3: Mppng Aury Sttsts for Dfferent Proessng Senros (ro =.) In gener, we oserved tht the omputed stndrd devtons for the estmted prmeters from unde djustment were pessmst when ompred to the error nyss presented n seton 3 nd the otned resuts for soute 3D mppng ury. It must e stressed out here tht our resuts nd onusons re sed on mppng from the two front mers. There s no gurntee tht the oresght quty s the sme for mers s network onnetvty ws dfferent for eh mer. It s requred to hve spe ontro fed to hve smr onnetvty for mers. 8. SUMMAY AND CONCLUSIONS Moe mppng systems re effetve toos for oetng up-todt GIS fetures. They provde fst nd ost effetve mppng souton. The devered ury s funton of nvgton souton ury, system rton, nd mppng sensor rton. Ths pper des wth system rton n whh the reton etween mer nd nvgton sensor re estmted. Dfferent proessng senros were tested. The ury sed on n ndependent hek ponts were omputed. The dfferene etween the dfferent senros s nsgnfnt, provded tht the rton ws done sed on suffent nd we dstruted numer of vn setups n ddton to urte, spty dstruted ontro fed. Fny, unde djustment ury mesures for the estmted prmeters were not rest nd the evuton of the quty must e sed on hek pont nyss. 9. ACKNOWLEDGEMENTS The uthors wsh to thnk the Cndn GEOIDE NCE nd NSEC for ther fnn support. Cmeron Eum s knowedged s the o-uthor of the Addnghm Smuton/Adjustment softwre sute used for dt proessng. Dr. Aymn H nd hs tem re so knowedged for performng mer rton.. EFEENCES Borre K., Epsod geometry nd onform mppng, Aorg Unversty, Deprtment of ommunton tehnoogy. [weste] (st essed 7--9) Eum, C.M. nd E-Shemy, N. (5). Integrtng photogrmmetry nd GPS t the mesurement-eve. Proeedngs of ION GNSS 5. Septemer 3-6, Long Beh, CA, USA. E-Shemy, N (996). The Deveopment of VISAT - A Moe Survey System for GIS Apptons, Ph.D. thess, The Unversty of Cgry, UCGE eport No. ( E-Shemy, N., (996). A Moe Mut-Sensor System For GIS Apptons In Urn Centers. The Internton Soety for Photogrmmetry nd emote Sensng (ISPS) 996, Commsson II, Workng Group, Vo. XXXI, Prt B, pp. 95-, Venn, Austr, Juy 9-9. E-Shemy, N., (5). An Overvew of Moe Mppng Systems. FIG Workng Week 5 nd GSDI-8, Cro, Egypt Apr 6-. Grejner-Brzeznsk, D. A., (999). Dret Exteror Orentton of Arorne Imgery wth GPS/INS system: Performne nyss, Nvgton, Vo. 46, No. 4, pp Grejner-Brzeznsk D., L,., H N., Toth C., (). Mut-Sensor Systems for Lnd-Bsed nd Arorne Mppng: Tehnoogy of the Future?. ISPS Commsson II, WGII/, Chn August -3,.

7 H, A., Lee, Y., Morgn, M.,. Bunde Adjustment wth Sef-Crton usng Strght Lnes. Photogrmmetr eord Journ, 7():635-65, Otoer. H, A., nd M. Morgn, 3, Automt Crton of Low-Cost Dgt Cmers, Journ of Opt Engneerng, 4(4): , Apr 3. H, A., nd M. Morgn, 4, Stty nyss nd geometr rton of off-the-shef dgt mers, Photogrmmetr Engneerng nd emote Sensng, 7, 6, June, 5, p Hepke, C., Josen, K., Wegmnn, H.(): The OEEPE-Test on Integrted Sensor Orentton Anyss of esuts, OEEPE-Workshop Integrted Sensor Orentton, Hnnover Sept. Josen, K., 3, System Crton for Dret nd Integrted Sensor Orentton, Theory, Tehnoogy nd etes of Inert/GPS Sensor Orentton. ISPS WG I/5, Breon, 3, 6S., CD. Meer, H.-K. (978), The Effet of Envronment Condtons on Dstorton, Crted Fo Length nd Fous of Aer Survey Cmers, ISP Symposum, Tokyo 978. Nssr, M. M., Advned geometr geodesy, 994, Leture notes, Futy of Engneerng, An Shms Unversty, Cro, Egypt. Shwrz K. P., E-Shemy N., (4). Moe Mppng Systems Stte of The Art nd Future Trends, ISPS Commsson 5, Istnu, Turkey. Shn, E-H. nd E-Shemy N., (4). Aded Inert Nvgton System (AINS ) Tooox for MtL Softwre. Moe Mut-Sensor Systems reserh group, the Unversty of Cgry, Cnd. reserh.htm (Aessed Apr 6). Skoud J. (999). Proems n Dret-Georeferenng y INS/DGPS n the Arorne Envronment. ISPS Workshop on "Dret versus Indret Methods of Sensor Orentton", WG III/I, Breon, 999. Wegmnn H., Hepke C., nd Josen K, (4). Dret Sensor Orentton Bsed on GPS Network Soutons. ISPS Commsson I, WG V, Istnu, Turkey. Ystk N. (4). The Effet of System Crton on Dret Sensor Orentton. ISPS Commsson I, WG V, Istnu, Turkey.