Influence of Control Points Configuration on the Mobile Laser Scanning Accuracy

Con en om his wo k may be used unde he e ms o heC ea i eCommonsA ibu ion 3.0 licence. Any u he dis ibu ion o his wo k mus main ain a ibu ion o he au ho (s) and he i le o he wo k, jou nal ci a ion and DOI. Published unde licence by IOP Publishing L d 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 1 In luence o Con ol Poin s Con igu a ion on he Mobile Lase Scanning Accu acy Pe Kal oda 1, Jakub Nosek 1, Pe a Kal odo a 1 1 B no Uni e si y o Technology, Ve e i 331/95, B no, Czech Republic kal oda.p@ u b .cz Abs ac . Mobile mapping sys ems (MMS) a e becoming widely used in s anda d geode ic asks mo e commonly in he las yea s. The pape is ocused on he in luence o con ol poin s (CPs) numbe and con igu a ion on mobile lase scanning accu acy. The mobile lase scanning (MLS) da a was acqui ed by MMS RIEGL VMX-450. The esul ing poin cloud was compa ed wi h wo di e en e e ence da a se s. The i s e e ence da a se consis ed o a high-accu acy es poin ield (TPF) measu ed by a T imble R8s GNSS sys em and a T imble S8 HP o al s a ion. The second e e ence da a se was a poin cloud om e es ial lase scanning (TLS) using wo Fa o Focus3D X 130 lase scanne s. The coo dina es o bo h e e ence da a se s we e de e mined wi h signi ican ly highe accu acy han he coo dina es o he es ed MLS poin cloud. The accu acy es ing is based on coo dina e di e ences be ween he e e ence da a se and he es ed MLS poin cloud. The e is a minimum numbe o 6–7 CPs in ou scanned a ea (based on MLS ajec o y leng h) o achie e he decla ed ela i e accu acy o ajec o y posi ioning acco ding o he RIEGL da ashee . We es ed wo ypes o g ound con ol poin (GCP) con igu a ions o 7 GCPs, using TPF e e ence da a. The i s ype is a ajec o y-based CPs con igu a ion, and he second is a geome y-based CPs con igu a ion. The accu acy di e ences o he MLS poin clouds wi h ajec o y-based CPs con igu a ion and geome y-based CPs con igu a ion a e no s a is ically signi ican . F om a p ac ical pe spec i e, a geome y-based CPs con igu a ion is mo e ad an ageous in he nonlinea ype o u ban a ea such as ou one. The ollowing analyzes a e pe o med on geome y-based CPs con igu a ion a ian s. We es ed he in luence o changing he loca ion o wo CPs om g ound o oo . The e ec o he e ical con igu a ion o he CPs on he accu acy o he es ed MLS poin cloud has no been demons a ed. The e ec o he numbe o con ol poin s on he accu acy o he MLS poin cloud was also es ed. In he o e all s a is ics using TPF, he accu acy inc eases signi ican ly wi h inc easing he numbe o GCPs up o 6. This numbe co esponds o a equi emen o he manu ac u e . Al hough u he inc easing he numbe o CPs does no signi ican ly inc ease he global accu acy, local accu acy imp o es wi h inc easing he numbe o CPs up o 10 (a e age spacing 50 m) acco ding o he compa ison wi h he TLS e e ence poin cloud. The accu acy es o he MLS poin cloud was di ided in o he ho izon al accu acy es on he açade da a subse and he e ical accu acy es on he oad da a subse using he TLS e e ence poin cloud. The esul s o his pape can help imp o e he e iciency and accu acy o he mobile mapping p ocess in geode ic p axis. 1. In oduc ion Mobile lase scanning (MLS) me hods ha e become widely used o cap u e accu a e 3D poin clouds o many applica ions, o example, u ban planning, 3D ci y modeling, ci il enginee ing, and oad su eying [1, 2, 3]. The geome ic accu acy o he inal p oduc is one o he undamen al p ope ies, 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 2 depends on a la ge numbe o ac o s. These ac o s a e he inpu da a accu acy, densi y, and he algo i hms used. The accu acy o MLS da a can be di ided in o absolu e and ela i e componen s, which co espond o he posi ioning subsys em and mapping subsys em o he mobile mapping sys em (MMS). The posi ioning subsys em uses an Ine ial Measu ing Uni (IMU), Global Na iga ion Sa elli e Sys em (GNSS), and Dis ance Measu emen Indica o s (DMIs) [4, 5]. The esul o GNSS, IMU, and DMI da a combina ion in a Kalman il e is Smoo hed Bes Es ima ed T ajec o y (SBET). The accu acy o SBET can be imp o ed by using con ol poin s (CPs) [6]. The mapping subsys em pe o ms he spa ial da a acquisi ion and ypically consis s o one o mo e LIDAR senso s and came as. Accu a e calib a ion o bo h subsys ems is a p e equisi e o accu a e geo e e enced LIDAR da a. Many au ho s ha e in es iga ed me hods o assessing and imp o ing he accu acy o MMS da a. The geome ic accu acy o he esul ing poin clouds is commonly imp o ed by using signalized CPs [7] obse ed in mul iple MMS passes [8, 9]. Inc easing he numbe o CPs leads o mo e di icul p ocesses and cos s. The aim is o minimize he numbe o con ol poin s o maximizing he e iciency o lase scanning and pho og amme y p ocesses [10]. Independen quan i ica ion o e o s is ealized using check poin s ( alida ion poin s) [9, 11]. Fo his pu pose, a es poin ield (TPF) can be c ea ed in he u ban e e ence a ea, h ough which he MMS can be d i en. To ensu e he necessa y eliabili y o he esul ing s a is ics, he TPF mus ha e a su icien densi y and a su icien ly high numbe o es poin s. The ad an age o TPF-based accu acy es ing is he abili y o de e mine he coo dina es o signaled check poin s wi h high accu acy. Howe e , TPF-based accu acy es ing may su e om he signi ican dispa i y in da a densi y be ween he MLS and he independen ly su eyed poin s. A dense e e ence poin cloud can be used o accu acy es ing o MLS as a a ian o TPF. The accu acy o he e e ence poin cloud should be highe han he accu acy o he es ed MLS poin cloud. The e e ence poin cloud is usually acqui ed by s a ic e es ial lase scanning (TLS). The accu acy es s o MLS da a can be based on a compa ison o TLS poin cloud wi h MLS poin cloud, and he me hods used o compa ison can a y. The TLS-based app oach does no su e om poo densi y and allows a be e local e o s e alua ion o he es ed poin cloud. The disad an age o he TLS-based app oach may be a la ge amoun o e e ence da a and lowe accu acy compa ed o he TPF-based app oach. Kaa inen e al. [12] es ed i e MMSs a 1700 m o he oad en i onmen . They quan i y ho izon al and e ical accu acy using independen ly su eyed poin ea u es ( e e ence objec s) like poles, cu b co ne s, and building co ne s ex ac ed om he poin cloud. The e ical accu acy was be e han ±35 mm up o a ange o 35 m (wi h all p o essional sys ems co ec ly calib a ed). The bes sys em had a ho izon al accu acy o ±25 mm, e en wi h a ange o 45 m, and e ical accu acy o ±1–2 cm wi h a ange o 35 m. Xu e al. [13] use o assess accu acy 45 con ol poin s and app oxima ely 90 ob ious ea u e poin s (such as building and window co ne s, poles, and a ic signs) in he TPF (app ox. a ea size 1700 m × 550 m). Thei TPF accu acy is in he o de o cen ime e s, and he esul ing accu acy o es ed da a is app ox. ±2 decime e s. Johnson e al. [9] in hei manual o MLS epo wo es poin s wi h checkpoin s, an u ban es si e, and a u al highway es si e o es he MMS pe o mance o ou comme cial endo s. The accu acy o ou MMS is es ed wi h signalized con ol poin s and TLS e e ence da a. Accu acies ob ained by design-g ade mobile mapping sys ems did no exceed ±80 mm in ho izon al componen and 50 mm in e ical componen (a he 95% p obabili y le el). 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 3 F yskowska and W óblewski [14] also use TLS e e ence da a o accu acy es ing o an MMS. Thei assessmen is pe o med using he leng hs o building ea u es (e.g., oo edges) and 395 check poin s. They analyzed poin clouds in e ms o objec iden i ica ion and geome ic po en ial (in many objec classes). The o e all ho izon al accu acy o he MLS poin cloud was ±60 mm, and he o e all e ical accu acy was ±42 mm. The pe cen age dis ibu ion o he e o s is also es ed. This pape aims o de e mine he in luence o CPs numbe and con igu a ion on mobile lase scanning local and global accu acy. In con as o o he wo ks, o es ing, we use high-accu acy TPF, which has se e al imes highe accu acy (±1.6 mm in ho izon al and ±1.4 mm in e ical componen ) han he es ed MLS poin cloud wi h he e e ence TLS poin cloud. 2. MMS desc ip ion The MMS RIEGL VMX-450 ( able 1) in eg a es wo RIEGL VQ-450 lase scanne s, a modula VMX- 450-CS6 came a sys em wi h ou indus ial came as, POINT GREY Ladybug5 sphe ical came a imaging sys em, GNSS/IMU na iga ion ha dwa e, dis ance measu emen uni VMX-450-DMI, and a po able con ol uni VMX-450-CU. Table 1. RIEGL VMX-450 echnical cha ac e is ics [7]. Senso P ope y name P ope y alue VQ-450 Measu ing p inciple Time o Fligh Max. measu emen a e 1.1 MHz (2×0.55 MHz), ρ ≥ 10 % up o 140 m Scan a e (selec able) up o 400 lines/sec Accu acy 8 mm, 1σ @ 50 m ange P ecision 5 mm, 1σ @ 50 m ange IMU/GNSS Absolu e posi ion accu acy 0.02–0.05 m, 1σ Rela i e posi ion accu acy 0.01 m, 1σ (wi h a CPs spacing <100 m) Roll and pi ch accu acy 0.005°, 1σ Yaw (heading) accu acy 0.015°, 1σ RIEGL de ines he accu acy in he da ashee [15] as a deg ee o con o mi y o measu ed quan i y o i s ue alue in he VQ-450 sec ion o able 1. The p ecision RIEGL de ines in da ashee [15] as epea abili y ( he deg ee o which u he measu emen s show he same esul ). Values in he IMU/GNSS sec ion o able 1 a e alid i he ollowing condi ions a e ul illed: no GNSS ou ages, DMI op ion, and pos -p ocessed using base s a ion da a. The ela i e posi ion accu acy alue in he IMU/GNSS sec ion o Table 1 is alid wi h a CPs spacing o less han 100 m. 3. Re e ence da ase s Two di e en e e ence da a se s we e used o accu acy es ing (TPF, TLS). The i s e e ence da a se consis ed o a high-accu acy es poin ield (TPF) measu ed by a T imble R8s GNSS sys em and a T imble S8 HP o al s a ion. The second e e ence da a se was a poin cloud om e es ial lase scanning (TLS) using wo Fa o Focus3D X 130 lase scanne s. Iden i iabili y o he poin s is an essen ial p ope y o esul ing accu acy. We can dis inguish wo ypes o poin iden i ica ion e o s o ou pu poses. The i s ype is an e o o iden i ica ion in eal-wo ld and he second ype is an e o o iden i ica ion in poin clouds. The esul ing poin coo dina es e o consis s o he iden i ica ion e o and used coo dina e de e mina ion me hod e o . Fo example, he e o o a poin de e mined by a o al s a ion is a ec ed by a poin iden i ica ion e o in he eal wo ld. The e o o a poin measu ed om a poin cloud is a ec ed by a poin iden i ica ion e o in a poin cloud. 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 4 In his pape , we ocus on he e o s o he me hod used. In he case o a TLS da ase , he cloud- o- cloud compa ison me hod elimina es he e o om iden i ying poin s. In he case o TPF, we used signaling a ge s o minimize he impac o iden i ica ion e o s. The TPF was c ea ed wi hin he acul y esea ch p ojec FAST-S-19-5704 “Geome ic accu acy o mobile mapping sys ems” o in e nal g an sys em o B no Uni e si y o Technology (BUT) in he a ea o Ad anced Ma e ials, S uc u es and Technologies (AdMaS) esea ch cen e. The TPF consis s o 214 poin s signalized and s abilized using checke boa d a ge s. Ho izon al a ge s (119) we e ma ked by whi e colo on asphal oadways ( igu e 1). The e ical a ge s (95) we e made o aluminum shee s ( igu e 1). Ve ical a ge s we e placed on buildings, e ical a ic signs, conc e e pilla s, and o he sui able e ical s uc u es. The a ge s on he buildings we e placed in wo heigh le els abo e he g ound: 2 m, 10 m. Figu e 1. Tes poin ield (le ), checke boa d a ge s (middle and igh ) The geode ic ne wo k and he es poin ield we e measu ed wi h high accu acy. T imble S8 HP o al s a ion and T imble R8s GNSS sys em we e used. Fi s ly, a pu pose-buil geode ic ne wo k was c ea ed. Secondly, es ield poin s we e de e mined. The coo dina es o he es ield poin s we e calcula ed by he geode ic ne wo k leas -squa es adjus men wi h a combina ion o GNSS and e es ial measu emen s. The Eu opean Te es ial Re e ence Sys em 89 (ETRS89) and Eu opean Te es ial Re e ence F ame 2000 (ETRF2000) we e used [16]. The minimum-cons ained ne wo k adjus men was used o compu ing o geode ic ne wo k. Inpu da a in adjus men was pola coo dina es measu ed by he o al s a ion and coo dina es o ou poin s de e mined by he s a ic GNSS me hod. The cons ained ne wo k adjus men was used o compu ing o es ield a ached o ixed poin s ( he geode ic ne wo k). The o e all accu acy o he es ield de e mined by adjus men can be exp essed as he es ima e o he 3D s anda d de ia ion s3D = ±2.0 mm. The es ima es o ho izon al, e ical, and 3D s anda d de ia ions (sHz, sV, and s3D) o bo h e e ence da ase s a e in able 2. Table 2. Accu acy o e e ence da ase s ho izon al sHz e ical sV 3D s3D TPF ±1.6 mm ±1.4 mm ±2.0 mm TLS poin cloud ±7.4 mm ±4.1 mm ±8.5 mm The TPF alues we e ob ained om he leas -squa es adjus men , while he TLS poin cloud alues we e ob ained om he di e ences be ween he e e ence coo dina es o he TPF poin s and hei coo dina es de e mined om he TLS poin cloud. The e o e he TLS poin cloud alues include e o s o TPF poin s iden i ica ion in he TLS poin cloud, so he eal accu acy o his da ase is sligh ly be e . 4. MMS da a acquisi ion and p ocessing MMS da a we e acqui ed by wo ehicle passes (in bo h di ec ions) 600 m long a a speed o 20 km/h. The scanned a ea dimensions a e app oxima e leng h 190 m, wid h 90 m, and heigh ange 20 m, 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 5 including buildings. Lase da a we e acqui ed a a equency o 1.1 MHz. The MMS ajec o y was calcula ed using Applanix POSPac. The GNSS Pos P ocessing Kinema ic me hod esul s we e e ined and smoo hed by a o wa d-backwa d Kalman il e using IMU and DMI da a. The p ocessing o MLS da a was pe o med in RIEGL RiPROCESS. RiPROCESS p ocessing consis s o da a con e sion, MLS poin clouds gene a ion, and ajec o y adjus men . In he i s s age, he MLS poin cloud was c ea ed based on he POSPac ajec o y. Fu he mo e, CPs and check poin s in he MLS poin cloud we e manually iden i ied. Mo e accu a e ajec o ies o di e en con igu a ions and CPs numbe s we e p ocessed using he RiPRECISION module based on co espondences be ween poin clouds and CPs. In his s ep, he ajec o ies can be e ined using CPs, which is essen ial, especially in en i onmen s wi h poo GNSS condi ions (e.g., u ban a eas). The esul ing poin clouds consis o wo pa ial poin clouds co esponding o wo ehicle passes and con ain mo e han 247,000,000 poin s wi h a densi y o abou 4 mm. Finally, MLS poin cloud il e ing is pe o med in he CloudCompa e 2.11 so wa e. 5. Accu acy e alua ion me hodology The accu acy e alua ion is based on a compa ison o he es ed MLS poin clouds a ian s wi h e e ence da ase s. TPF-based es ing uses he di e ences be ween he e e ence coo dina es o he TPF poin s and hei coo dina es de e mined om he MLS poin cloud. TLS-based es ing uses a compa ison o he TLS e e ence poin cloud wi h he MLS poin clouds in CloudCompa e 2.11 so wa e. The di e ences be ween he clouds we e es ima ed using he Cloud- o-Cloud Dis ance unc ion wi h local modeling using he Leas Squa es Plane [17]. The poin clouds we e di ided in o he açade da a subse and he oad da a subse in he TLS-based accu acy es ing. Ho izon al accu acy was es ed on a açade da a subse and e ical accu acy on a oad da a subse . The leng h o he selec ed açade is 80 m and he heigh 9 m. We use es ima es o ho izon al, e ical, and 3D s anda d de ia ions (68% con idence in e al) o accu acy cha ac e is ics. We es he ela i e numbe o s aggle s (α = 5 % c i ical alue) and ou lie s (α = 1 % c i ical alue) acco ding o [18]. The con ol poin s we e no used as check poin s o ensu e independen accu acy e alua ion. The e is a minimum numbe o 6–7 CPs in ou scanned a ea (based on MLS ajec o y leng h) o achie e he decla ed ela i e accu acy o ajec o y posi ioning acco ding o he RIEGL da ashee . The GNSS/IMU ela i e posi ioning unce ain y (±10 mm, 68% con idence in e al) is unde he condi ion o a CPs spacing <100 m. We es ed wo ypes o GCPs con igu a ions o 7 GCPs, using TPF e e ence da a. The i s ype is a ajec o y-based CPs con igu a ion, and he second is a geome y-based CPs con igu a ion. We es ed he s a is ical signi icance o accu acy di e ences o he MLS poin clouds wi h ajec o y-based CPs con igu a ion and geome y-based CPs con igu a ion using he F- es [19]. Also, he in luence o changing he loca ion o wo CPs om g ound o oo and he e ec o he numbe o CPs on he global accu acy o he MLS poin cloud was es ed using F- es . 6. Resul s The esul s a e di ided in o wo subsec ions acco ding o he used e e ence da ase . 6.1. TPF-based accu acy es The accu acy es ima es o ajec o y-based and geome y-based GCPs con igu a ions o 7 GCPs, using TPF e e ence da a, a e in able 3. The ela i e numbe s o s aggle s and ou lie s a e in able 4. The con igu a ions o GCPs (ma ked wi h ed do s) a e shown in igu e 2. 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 6 Table 3. TPF-based accu acy o ajec o y-based and geome y-based GCPs con igu a ions ho izon al sHz e ical sV 3D s3D T ajec o y-based (7 GCPs) ±18 mm ±8.1 mm ±20 mm Geome y-based (7 GCPs) ±16 mm ±8.6 mm ±19 mm Table 4. S aggle s and ou lie s o ajec o y-based and geome y-based GCPs con igu a ions ho izon al e ical 3D s aggle s ou lie s s aggle s ou lie s s aggle s ou lie s T ajec o y-based (7 GCPs) 0 % 0 % 1 % 4 % 0 % 0 % Geome y-based (7 GCPs) 1 % 0 % 3 % 3 % 0 % 0 % Figu e 2. O e iew o ajec o y-based (le ) and geome y-based ( igh ) GCPs con igu a ions The accu acy di e ences o he MLS poin clouds wi h ajec o y-based CPs con igu a ion and geome y-based CPs con igu a ion a e no s a is ically signi ican . F om a p ac ical pe spec i e, a geome y-based CPs con igu a ion is mo e ad an ageous in he nonlinea ype o u ban a ea such as ou one. The ollowing analyzes a e pe o med on geome y-based CPs con igu a ion a ian s. The e ec o changing he loca ion o wo CPs om he g ound o he oo is shown in able 5. Va ian s wi h only GCPs a e ma ked as g ound, and a ian s wi h wo GCPs eplaced by oo CPs a e called he oo . The con igu a ions o CPs a e shown in igu e 3. Table 5. TPF-based accu acy – in luence o wo GCPs eplacing by oo CPs ho izon al e ical 3D g ound oo g ound oo g ound oo 6 CPs ±16 mm ±17 mm ±8.2 mm ±9.0 mm ±18 mm ±19 mm 10 CPs ±15 mm ±15 mm ±8.2 mm ±9.1 mm ±17 mm ±17 mm Figu e 3. The con igu a ions o GCPs ( ed and blue) wi h g een oo CPs ( eplacing blue GCPs) 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 7 The maximum di e ence o s aggle s and ou lie s o g ound and oo a ian s is 2 %. The accu acy di e ences o he MLS poin clouds (g ound and oo CPs a ian s) a e no s a is ically signi ican . The e ec o changing he loca ion o wo CPs om he g ound o he oo on he accu acy o he es ed MLS poin cloud has no been demons a ed. The esul s o he TPF-based global accu acy es o a ious numbe s o GCPs ( ed do s) a e shown in able 6. The con igu a ions o CPs a e shown in igu e 4. Table 6. TPF-based accu acy – a ious numbe s o GCPs Check poin s numbe ho izon al sHz e ical sV 3D s3D 0 GCPs 204 ±36 mm ±127 mm ±130 mm 1 GCPs 203 ±26 mm ±42 mm ±59 mm 2 GCPs 202 ±32 mm ±43 mm ±64 mm 3 GCPs 201 ±18 mm ±33 mm ±49 mm 4 GCPs 200 ±17 mm ±59 mm ±59 mm 5 GCPs 199 ±20 mm ±37 mm ±51 mm 6 GCPs 198 ±16 mm ±30 mm ±48 mm 7 GCPs 197 ±16 mm ±30 mm ±46 mm 10 GCPs 194 ±15 mm ±32 mm ±46 mm 13 GCPs 191 ±14 mm ±34 mm ±43 mm Figu e 4 The con igu a ions o a ious numbe s o GCPs In he o e all s a is ics using TPF, he accu acy inc eases signi ican ly wi h inc easing he numbe o GCPs up o 6. This numbe co esponds o a equi emen o he manu ac u e (CPs spacing <100 m). The maximum di e ence o s aggle s and ou lie s o 6 GCPs and mo e GCPs a ian s is 1 %. Inc easing he numbe o CPs o e six does no signi ican ly inc ease global accu acy. 6.2. TLS-based accu acy es The esul s o he TLS-based es o he oad da a subse ( e ical accu acy) and he açade da a subse (ho izon al accu acy) a e in able 7. 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 8 Table 7. TLS-based accu acy – a ious numbe s o GCPs ho izon al sHz e ical sV 6 GCPs ±14 mm ±7.7 mm 7 GCPs ±14 mm ±7.4 mm 10 GCPs ±6.1 mm ±7.7 mm 13 GCPs ±5.9 mm ±7.9 mm The maximum ela i e numbe o s aggle s is 3 %, o ou lie s is 2 %. The di e ence o s aggle s and ou lie s o 6 GCPs and mo e GCPs a ian s is 0.5 %. Al hough inc easing he numbe o GCPs o e six does no signi ican ly inc ease he global accu acy, local accu acy imp o es wi h inc easing he numbe o CPs up o 10 (a e age spacing 50 m). This ac is e iden om he açade s a is ics in able 7 and he isualiza ions o he di e ences in igu e 5 and igu e 6 (poin s wi h di e ences > 20 mm a e ma ked in ed). Figu e 5. TLS-based es ing – oad da a subse ( e ical accu acy) Figu e 6. TLS-based es ing – açade da a subse (ho izon al accu acy), 6, 7, 10, and 13 GCPs subsequen ly 7 h Wo ld Mul idisciplina y Ea h Sciences Symposium (WMESS 2021) IOP Con . Se ies: Ea h and En i onmen al Science 906 (2021) 012091 IOP Publishing doi:10.1088/1755-1315/906/1/012091 9 7. Conclusions The use o CPs signi ican ly helps o inc ease he MLS accu acy, especially in en i onmen s wi h poo GNSS condi ions (e.g., u ban a eas). The e o e we es ed he in luence o CPs con igu a ion and numbe on he MLS poin cloud accu acy. The accu acy e alua ion is based on compa ison o he es ed MLS poin clouds a ian s wi h e e ence da ase s (TPF and TLS). The poin clouds we e di ided in o he açade and he oad da a subse s o TLS-based accu acy es ing. Ho izon al accu acy was es ed on a açade da a subse and e ical accu acy on a oad da a subse . The accu acy di e ences o he MLS poin clouds wi h ajec o y-based CPs con igu a ion and geome y-based CPs con igu a ion a e no s a is ically signi ican . F om a p ac ical pe spec i e, a geome y-based CPs con igu a ion is mo e ad an ageous in he nonlinea ype o u ban a ea such as ou one. Also, he e ec o changing he loca ion o wo CPs om he g ound o he oo on he accu acy o he es ed MLS poin cloud has no been demons a ed. In he o e all s a is ics using TPF, he accu acy inc eases signi ican ly wi h inc easing he numbe o GCPs up o 6. This numbe co esponds o a equi emen o he manu ac u e (GCPs spacing <100 m). Al hough inc easing he numbe o GCPs o e six does no signi ican ly inc ease he global accu acy, he esul s o he TLS-based accu acy es shows ha local accu acy imp o es wi h inc easing he numbe o CPs up o 10 (a e age spacing 50 m). The achie ed accu acy wi h a spacing o CPs 100 m is su icien o mos mapping pu poses. 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