DEVELOPMENT OF TERRESTRIAL LASER SCANNERS CALIBRATION METHODOLOGY AND SCANNING TECHNOLOGY APPLICATIONS FOR GROUND SURFACE MODELLING

Transcription

1 VILNIUS GEDIMINAS TECHNICAL UNIVERSITY Dominykas ŠLIKAS DEVELOPMENT OF TERRESTRIAL LASER SCANNERS CALIBRATION METHODOLOGY AND SCANNING TECHNOLOGY APPLICATIONS FOR GROUND SURFACE MODELLING SUMMARY OF DOCTORAL DISSERTATION TECHNOLOGICAL SCIENCES, MEASUREMENT ENGINEERING (10T) Vilnius 2013

2 Dissertation was prepared at Vinius Gediminas Technical University in Scientific Supervisor Prof Dr Eimuntas Kazimieras PARŠELIŪNAS (Vilnius Gediminas Technical University, Technological Sciences, Measurement Engineering 10T). The dissertation is being defended at the Council of Scientific Field of Measurement Engineering at Vilnius Gediminas Technical University: Chairman Prof Dr Habil Jonas SKEIVALAS (Vilnius Gediminas Technical University, Technological Sciences, Measurement Engineering 10T). Members: Assoc Prof Dr Domantas BRUČAS (Vilnius Gediminas Technical University, Technological Sciences, Measurement Engineering 10T), Dr Habil Saulius ŠLIAUPA (Nature Research Center, Physical Sciences, Geology 05P), Prof Dr Habil Vladas VEKTERIS (Vilnius Gediminas Technical University, Technological Sciences, Mechanical Engineering 09T), Prof Dr Habil Pawel Aleksander WIELGOSZ (University of Warmia and Masuria in Olsztyn, Technological Sciences, Measurement Engineering 10T). Opponents: Prof Dr Habil Vygantas Stasys AUGUTIS (Kaunas University of Technology, Technological Sciences, Measurement Engineering 10T), Prof Dr Habil Algimantas ZAKAREVIČIUS (Vilnius Gediminas Technical University, Technological Sciences, Measurement Engineering 10T). The dissertation will be defended at the public meeting of the Council of Scientific Field of Measurement Engineering in the Senate Hall of Vilnius Gediminas Technical University at 10 a. m. on 12 December Address: Saulėtekio al. 11, LT Vilnius, Lithuania. Tel.: , ; fax ; doktor@vgtu.lt The summary of the doctoral dissertation was distributed on 11 November A copy of the doctoral dissertation is available for review at the Library of Vilnius Gediminas Technical University (Saulėtekio al. 14, LT Vilnius, Lithuania). Dominykas Šlikas, 2013

3 VILNIAUS GEDIMINO TECHNIKOS UNIVERSITETAS Dominykas ŠLIKAS ANTŽEMINIŲ LAZERINIŲ SKENERIŲ KALIBRAVIMO METODIKOS PARENGIMAS IR SKENAVIMO TECHNOLOGIJOS TAIKYMAI ŽEMĖS PAVIRŠIUI MODELIUOTI DAKTARO DISERTACIJOS SANTRAUKA TECHNOLOGIJOS MOKSLAI, MATAVIMŲ INŽINERIJA (10T) Vilnius 2013

4 Disertacija rengta metais Vilniaus Gedimino technikos universitete. Mokslinis vadovas: prof. dr. Eimuntas Kazimieras PARŠELIŪNAS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, matavimų inžinerija 10T). Disertacija ginama Vilniaus Gedimino technikos universiteto Matavimų inžinerijos mokslo krypties taryboje: Pirmininkas: prof. habil. dr. Jonas SKEIVALAS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, matavimų inžinerija 10T). Nariai: doc. dr. Domantas BRUČAS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, matavimų inžinerija 10T), habil. dr. Saulius ŠLIAUPA (Gamtos tyrimų centras, fiziniai mokslai, geologija 05P), prof. habil. dr. Vladas VEKTERIS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, mechanikos inžinerija 09T), prof. habil. dr. Pawel Aleksander WIELGOSZ (Varmijos ir Mozūrijos universitetas Olštyne, technologijos mokslai, matavimų inžinerija 10T). Oponentai: prof. habil. dr. Vygantas Stasys AUGUTIS (Kauno technologijos universitetas, technologijos mokslai, matavimų inžinerija 10T), prof. habil. dr. Algimantas ZAKAREVIČIUS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, matavimų inžinerija 10T). Disertacija bus ginama viešame Matavimų inžinerijos mokslo krypties tarybos posėdyje 2013 m. gruodžio 12 d. 10 val. Vilniaus Gedimino technikos universiteto senato posėdžių salėje. Adresas: Saulėtekio al. 11, LT Vilnius, Lietuva. Tel.: (8 5) , (8 5) ; faksas (8 5) ; el. paštas Disertacijos santrauka išsiuntinėta 2013 m. lapkričio 11 d. Disertaciją galima peržiūrėti Vilniaus Gedimino technikos universiteto bibliotekoje (Saulėtekio al. 14, LT Vilnius, Lietuva). VGTU leidyklos Technika 2186-M mokslo literatūros knyga. Dominykas Šlikas, 2013

5 Introduction Topicality of the problem. To solve many practical tasks, which appear due to various human activities is possible by the help of the geodetic measurements performance which later according to the parameters values of the points of the measured targets, which comprise spatial data, make it possible to compile spatial (3D dimensional) models, which could more closely describe the objects of the real world. Application of the spatial model creates available technological preconditions for the solution of various technical tasks, e.g., preservation of architectural objects, designing of the technically complicated targets and etc. During the two recent decades, there appeared great changes in the field of Engineering Geodesy regarding equipment, devices and instruments. The spatial data collecting methods have undergone great changes with the application of laser scanning, which allows during the short time to store huge amount of information regarding the shape of the analysed object and its parameters. The scanning facilities accumulate data of the objects without any physical approach. Laser scanners are used in architecture, construction, aviation, transport, culture, archaeology, forestry and the other fields. In some fields, it is required high accuracy of the measured parameters, when the errors comprise several millimeters or even their parts, in some other fields it is enough several or even few tens of millimeters. In order to reduce the influence of the systematic and random errors of the measuring devices on the measured values, it is required to perform calibration of the measuring instruments. The work deals with the working out of the terrestrial laser scanners calibration methodology when applying present methodology of calibration of the electronic distance meters. Also the doctorial work analyses the peculiarities of laser scanning technology, which originated while performing the experimental part of work. When analysing spatial data accumulated by scanning technology there have been assessed random big errors, which have been eliminated according to the compiled algorithm. The laser scanning technology has been adapted to the cartography of the cultural targets. Also there has been proposed the algorithm to generate the open space surface model, which supplements the Earth s surface (digital surface model DSM) and the relief surface (Digital Terrain Model DTM) model group. Relevance of the work. The calibration of terrestrial laser scanners is an intermediate link when performing the measurements of the terrestrial target 5

6 parameters. When calibrating, it is required to assess the systematic and random errors of separate measuring systems (distance measuring systems and angle measuring systems). The calibration of terrestrial laser scanners from the point of view of accuracy ensures the acquiring of high quality laser scanning data to be applied in modelling the Earth s surface. Research object. The methodology of the terrestrial laser scanners calibration and the analysis and assessment of terrestrial laser scanning technology for the Earth s surface modelling. Aim of the work. To work out the methodology of terrestrial laser scanner calibration, by applying the existing methodology of the electronic distance meter calibration, without specified laboratories. Tasks of the work. The following tasks were investigated in order to achieve the objective of the work: 1. To work out the methodology of terrestrial laser scanner calibration by applying the present available methodology of electronic distance meter calibration. 2. To carry out the experimental terrestrial laser scanner calibrations, seeking to verify the worked out calibration methodology of the terrestrial laser scanners. 3. To improve the laser scanning technology for the Earth s surface modelling. Methods of the work. The methodology of electronic distance meters calibration and methods of the Earth s surface modelling were applied. Scientific novelty. The doctoral dissertation work presents the acquired scientifically new results for measurements engineering: 1. There was compiled the methodology of terrestrial laser scanner calibration based on the technology when the distance and angular measuring systems are calibrated separately. Also, in this methodology the possibility to perform the calibration procedure in the field conditions is foreseen. 2. There was suggested the method for determining the zero position on the vertical scale of the circle in the vertical angle measuring system of terrestrial laser scanners, which ensures the most reliable final measuring results. 6

7 3. There was compiled the algorithm to filter big (systematic and random) errors of terrestrial laser scanning data, which improves the quality of the Earth s surface models. 4. There was suggested and verified the technology for compiling the model of the open space surface, which supplements the Earth s surface models family. Practical value. The results of the performed doctorial work makes it possible to adapt for legitimizing the methodology of terrestrial laser scanners. It was improved the laser scanning technology for compiling the open space surface model, thus complimenting the group of the available digital models of the Earth s surface. Defended propositions 1. When applying the suggested calibration methodology of horizontalvertical angle measuring system it is possible to determine the systematic errors of the horizontal and vertical angle measuring systems of terrestrial laser scanners. 2. When applying the proposed methodology for determining the zero position on the vertical circle scale of the vertical angle measuring systems it is possible to determine the zero position of the vertical circle scale of terrestrial laser scanner. 3. When calibrating terrestrial laser scanners it is necessary to investigate separately the equipment and device systems for measuring of distances and angles. 4. When applying the suggested big error filtration algorithm it is possible to eliminate big errors (systematic and random) in the measurements data, when analysing the accrued data by means of laser scanning technology. 5. When applying the suggested algorithm it is possible to compile the open space surface model based on the spatial data accrued by laser scanning technologies. The scope of the scientific work. Doctoral dissertation consists of introduction, 3 chapters and generalization of the results. The research consists of 117 pages; the text includes 62 numbered formulas, 55 figures and 28 tables. The lists of publications and literature comprise 105 items and serve an important source when working on the research study. 7

8 1. Terrestrial laser scanner technology evolution The first chapter deals with the review of the available literature sources. It presents the analysis of the terrestrial laser scanners development and generalization, the accuracy of laser scanners is investigated. There were evaluated the structural peculiarities of terrestrial laser scanners and clarified their measured parameters. Legal sources on terrestrial laser scanner calibration methods and baseline were analysed, as well as the achievements of Lithuanian and foreign authors in the field of terrestrial laser scanner calibration. The attained results concerning the implementation of laser scanner technologies for modelling the Earth s surface were reviewed. 2. Terrestrial laser scanner calibration methodology development The second chapter of the work presents the developed methodology for calibration of terrestrial laser scanners, with the help of which, the evaluation is made of the accuracy of the distance measurements of terrestrial laser scanners as well as of the accuracy of angle measurements under in-site or field conditions. It does not require indoor premises, but could be used in the baseline calibration base for electronic distance meters. When performing the calibration of terrestrial laser scanners it is necessary to have the length baseline. The greater part of methodology would be oriented towards Vilnius Gediminas Technical University, Calibration Laboratory of Geodesy Institute, fort the available measures and means of calibration i.e. Kyviškės calibration baseline and cyclic error detection baseline. The calibration of distance measuring systems is required to be performed within all the range of distance measuring system of terrestrial laser scanner, it means that the shortest calibrated line and the longest one have to be as close as possible to the margins of the range of distance measuring system of terrestrial laser scanner. During the calibration procedure, it is required to use the same targets for the same device along all the lines. The angle measuring system of terrestrial laser scanners consists of vertical and horizontal angle measuring systems. This doctorial work analyses the calibration of horizontal angle measuring systems. The studied publications mainly deal with the analysis of angle measuring system calibration when the real angle value on the calibration baseline is known. The work proposes the method when the most reliable value of angle is calculated in terms of laser scanner measured distances. The calibration of angle measuring system of terrestrial laser scanners is suggested to be performed by measuring two targets, attached to the one of the 8

9 segments of the geodetic stations of the calibration base. Terrestrial laser scanner is located in front of both the targets in such a way as the distances between the terrestrial laser scanner and targets could coincide with the calibration distances of the distance measuring systems (Fig. 1). Points of calibration baseline with targets Positions of laser scanner Fig. 1. The calibration scheme of the horizontal angle measuring system of terrestrial laser scanner It is recommended to execute calibration when measuring several different angles, namely by reducing the distance to both targets, thus the measured angle tends to be increased. The distances between terrestrial laser scanner and the targets are selected such as they have to be close to the distances indicated on the certificate of calibration of distance measuring system, and the most reliable systematic corrections of which are determined by calibrating the distance measuring system. By the software of terrestrial laser scanner, the data of the measurements are read (rectangular coordinates). By applying the formulae of trigonometry there are calculated the measured distances between the terrestrial laser scanner and targets and the horizontal angles between the directions towards the targets: Y Y SK Y Y T SK 2 T1 β = arctan arctan, (1) X X SK X X SK T2 T1 where X SK, Y SK are the coordinates of terrestrial laser scanner station coordinates ; X Y, X, Y the coordinates of target centres. T, 1 T1 T2 T2 9

10 After calculating the horizontal angle ) terrestrial laser scanner and targets and S 1 i β i and distances between the ), it is required to correct the measured distances according to the correction model of the distance measuring system and calculate the most reliable value of the angle according to the trigonometry formulae. When there is a triangle with one baseline line, which is between T 1 and T 2 targets and corrected distances S 1p and S 2p, then it is possible to calculate the most reliable value of the angle β t and compare it with the measured angle β i (Fig. 2). S 2 i T 1 S E T 2 S 1p S 2p β t SK Fig. 2. Calculation scheme of the most reliable horizontal angle value In Fig. 2, T 1 and T 2 are the targets, SK station of the terrestrial laser scanner S1p + S2 p SE t = arccos 2S1p S2 p β, (2) where S 1 p is the distance of the first triangle side measured by the scanner and corrected; S 2 p is the distance measured by the scanner and corrected of the second side of the triangle; S E is the standard line of calibration baseline. The calculated measured angles have to be compared with the calculated reliable angles and the obtained results have to be generalized by calculating their accuracy parameters. 10

11 In the second chapter, there is submitted the experimental calibration of terrestrial laser scanners for these devices: Leica Scanstation C10, Faro Focus3D and Riegel LMS Z420i. The calibration of terrestrial laser scanners performed in the accredited Calibration laboratory of Vilnius Gediminas Technical University, Geodesy Institute (Fig. 3). The laboratory has cyclic error detection baseline and Kyviškės calibration baseline. The baseline of cyclic error detection is 15 m length, it consists in the 16th hinge mounted points at every meter. Kyviškės baseline is 1320 m length, with 6 poles in one line. a) b) Fig. 3. Views of point clouds acquired during calibration process of terrestrial laser scanners (a at cyclic error detection baseline, b at Kyviškės calibration baseline) Systematic error of distances, mm. The systematic errors, which were determined at cyclic error detection baseline by terrestrial laser scanners, are presented in Fig. 4, and at Kyviškės calibration baseline in Fig Leica Scanstation C10 2 Faro Focus3D 0-2 Riegel LMS Z420i Calibrated distance, m Fig. 4. Diagram of the systematic errors of terrestrial laser scanners determined at cyclic error detection baseline 11

12 Systematic error of distances, mm Calibrated distance, m 12 Leica Scanstation C10 Faro Focus3D Riegel LMS Z420i Fig. 5. Diagram of systematic errors of terrestrial laser scanners determined in Kyviškės calibration baseline The calibration of horizontal angle measuring system of terrestrial laser scanner was performed in Kyviškės calibration baseline. The measurements are made by attaching targets on the calibration base stations No. 5 and No. 6 between which the distance is known, the scanner is located in front these stations. After application of horizontal angle measuring system calibration method there were calculated the most reliable mean values of horizontal angles and measured horizontal angles according to which there were calculated the most reliable systematic errors of horizontal angle measuring system of terrestrial laser scanners which are presented in Table 1. Table 1. Systematic corrections of horizontal angle measuring system of terrestrial laser scanners Distance from the scanner till The most reliable correction of the measured angle β, targets, m Leica Scanstation C10 Faro Focus 3D Riegel LMS Z420i In the analysed literature sources of angle measuring system calibration there were indications that calibration was made in special baselines under laboratory conditions. The doctorial work proposes the method when for the calibration of angle measuring system there is adapted calibration base of the electronic distance meter.

13 3. Laser scanner technology implementation for the Earth s surface modelling Recently, the technology of laser scanning is widely spread in architecture, construction, aviation, quarries and etc. In the work there were analysed some fields of application of laser scanning technology for cultural object mapping, for filtration of big errors (systematic and random) from the accumulated data of laser scanning technologies, application of laser scanning data for modelling open space surface. When analysing the data of 3D models compiled for the locality with the help of spatial scanning data technologies there were noticed the following problems: Unqualified sorted points according to the Earth s surface object types; The Earth s surface points in one square meter are less, than there are determined in the technical requirements; There are points, the elevations of which do not correspond the prevailing elevations of the locality, therefore there are big errors. The doctorial work presents the algorithm of big error filtration. The algorithm was tested in a detailed way with various surfaces. The sample for that served Vilnius city data cloud of one nomenclature page (Fig. 6). a) b) Fig. 6. Diagram of real data point cloud (a with big errors; b after the detection and elimination of big errors) 13

14 The influence of big errors is obvious, when the real data point cloud with big errors is proved to be related with orthophoto map. After the analysis of big errors there were eliminated critical points, there was obtained a corrected digital model of the location (Fig. 7). a) b) Fig. 7. Picture of the real data point cloud and orthophoto map (a with big errors; b after the detection and elimination of big errors) After testing the algorithm with all the selected surfaces it is possible to state that the algorithms comprehensively met the goals and therefore, it is suitable for big error filtration by laser scanning technologies in the accumulated data. 14

15 The third chapter analyses the problem about cultural heritage objects the conditions of which are very bad both in Lithuania and worldwide. Therefore, it is necessary with all the possible measures to preserve the relics of cultural heritage. One of the measures is the compiling of 3D model for the object with the help of accrued data of terrestrial laser scanning. One of such cultural heritage objects is the chapel of the XVIII century (Fig. 8) not far from Musninkai village, and related to the Great Duchess of Lithuania, the Qeen of Poland Barbora Radvilaitė. The geodetic measurements were performed by two geodetic instruments: terrestrial laser scanner and total station. Fig. 8. Cross-sectional places of the chapel The measurements were performed by applying Leica company geodetic instruments electronic tachometer Leica TS30 and terrestrial laser scanner Leica Scanstation C10. The comparison of the obtained results are presented in Table 2. 15

16 Table 2. Comparison of the results acquired by different geodetic instruments Results of the terrestrial Results of the total station Crosssection δ=tls - TS laser scanner (TLS) (TS) X, Y, S, β, X, Y, S, β, δx, δy, δs, δβ, No. mm mm mm " mm mm mm " mm mm mm Mean of differences Standard deviation According to the obtained comparisons it is possible to state that the differences among the results obtained by diverse measuring devices are insignificant and are up to 13 mm on the projection, the inclination from the vertical is about 1.5 minutes. The obtained generalized inclination of the chapel is about 1.5 degree in the North West direction along all the height of the chapel. The third chapter of the doctorial work analyses laser scanning data application in modelling the open space surface. The open space is characterized as the space which is restricted by the surface, transient physical surface of the Earth s, on the surface of natural and artificial objects and the distances in which between these irregularities of the surfaces are not lower than the prescribed tolerances. In other words the moving objects of certain dimensions could freely move in such open space. In practice the concept of open space could be wider, say a plane could fly under the bridge if it is enough place, however the suggested open space model does not foresee that, because it will be limited by the surface of the bridge. In undeveloped places and not in the areas of forests, the surface of the open space coincides with the digital terrain surface and in the territory of the forest it will pass over the trees, in towns it will pass over the roofs of the buildings. Therefore, open space model is more similar to digital surface model and especially to the map of obstacles in the airports. But the compilers of such maps did not take into consideration the sizes of the moving objects (Fig. 9). 16

17 Fig. 9. Cross-section of digital surface model, digital terrain model and open space model When analysing there was noticed, that in compiling 3D model of the locality according to the accrued data of laser scanning method (1 point in 2 square meters) there were consumed huge time and computer resources. Due to these reasons there was developed the simplified algorithm of open space 3D model compiling LIDAR surface profile open space surface profile Fig. 10. Diagram of the profile over the building The main parameter of the simplified algorithm according to which the excess data are eliminated, is the size X of the object moving in the open space. For ensuring the specification of the open space it is necessary to know 17

18 minimum distance X between the nature and artificially created by a man objects. When eliminating the excess points there is also compiled a regular grid of squares. By applying the algorithm in each square of the grid there are selected the appearing there points accumulated by laser scanning method. From the selected points for each square there are selected the maximum values of elevations and they are prescribed to the points of the square canters. Thus, the algorithm, the points of the data file for the area of the covered locality, make as a square net and for each square (cell) presents the coordinates of the central and the attached maximum elevation values from the values of the elevations of points located in the square. In order to analyse more extensively open space 3D model there were compiled two profiles of the open space model and digital surface model. They pass over the building and over the railway. The profiles are presented in Fig. 10 and LIDAR surface profile open space surface profile Fig. 11. Diagram of the profile over the railway After the analysis of the profiles, there was noticed that in some places (Fig. 10 points 11 and 12) the obstacles remain in the open space. Thus, the algorithm of the open space model compiling had to be perfected. That 18

19 procedure could be implemented by adding on the cell sides the maximum elevation values. Although the number of points could increase by four times, but open space 3D model could be without ant obstacles. It is important to notify that some obstacles such as towers, antenna, poles and etc. have to be included into data collecting process by the manual method because laser scanning technology is unable to notice such objects. General conclusions 1. By applying the suggested methodology for the calibration of the terrestrial laser scanners, it is possible to perform the calibration of laser scanners at the calibration baseline of the electronic distance meters without the usage of any specified laboratory equipment. 2. The suggested methodology has been verified at the accredited calibration laboratory and it has been determined, that the methodology is considered to be suitable for the calibration of all available terrestrial laser scanners used for geodetic measurements at present. The accuracy of such measurements amounts to mm and is lower than the accuracy of calibration at the calibration baseline of the electronic distance meters. 3. By applying the suggested algorithm for determining and eliminating of big errors, the peculiarities of the relief forms irregularities moulded by glaciers have been evaluated, and thus, the most reliable data set for the Earth s surface modelling has been acquired. The data sets without the eliminated big errors have been developed during the process of experimental investigations. 4. The concept of the open space has been proposed and the method for compiling the open space 3D model has been developed, thus complimenting the group of the available digital models of the Earth s surface. The open space model differs from the other models and it is considered to be an innovation because it is determined by the cell size, defining the minimal possible open space volumes, and it is free from the spatial obstacles as well. List of published works on the topic of the dissertation In the reviewed scientific periodical publications Kalantaitė, A.; Putrimas, R.; Šlikas, D Application of LIDAR data for creating three-dimensional models of the site, Geodesy and Cartography, 36(4): (in Lithuanian). ISSN (Compendex) 19

20 Kalantaitė, A.; Paršeliūnas, E., K.; Romanovas, D.; Šlikas, D Generating the open space 3d model based on LiDAR data, Geodesy and Cartography, 38(4) ISSN (Compendex) Antanavičiūtė, U.; Obuchovski, R.; Paršeliūnas, E., K.; Popovas, D.; Šlikas, D Some issues of the calibration of the Terrestrial Laser Scanner Leica Scanstation C10, Geodesy and Cartography, 39(3) ISSN (Compendex) In the other editions Kalantaitė, A.; Šlikas, D The analysis of data collected applying LIDAR method. The 8-th International Conference Environmental Engineering Selected Papers, Vol. 3, Vilnius Gediminas Technical University Press Technika, 2011, p About the author Dominykas Šlikas acquired the bachelor s qualification degree in measurement engineering in Vilnius Gediminas Technical University in 2005, and in 2007 he acquired master s qualification degree in measurement engineering. From 2009 to 2013 he was a doctorial student at Vilnius Gediminas Technical University. In 2011 he was at training courses in the Laboratory of the geometric documentation of Heritage of the University of the Basque Country. At present Dominykas Šlikas is an engineer at Geodetic Institute of Vilnius Gediminas Technical University. Letter of thanks My sincere regards to the work supervisor Prof Dr Eimuntas Kazimieras Paršeliūnas for the valuable and original scientific ideas. I would like to thank for the assistance, remarks and recommendations during the working process on the doctoral thesis. I would like to express my gratitude to the colleges, co-workers, my family and friends, all who supported me in my work. I would like to thank UAB GPS partneris and UAB Terra Modus for the possibility to perform experiments with the state-of-art terrestrial laser scanners. ANTŽEMINIŲ LAZERINIŲ SKENERIŲ KALIBRAVIMO METODIKOS PARENGIMAS IR SKENAVIMO TECHNOLOGIJOS TAIKYMAI ŽEMĖS PAVIRŠIUI MODELIUOTI Problemos formulavimas. Sprendžiant daugelį praktinių uždavinių, kylančių įvairiausiose žmonių veiklos srityse, dažnai atliekami geodeziniai matavimai ir pagal išmatuotų objektų taškų parametrų vertes, kurios sudaro erdvinius duomenis, reikia sukurti erdvinius (trimačius) modelius, kurie kiek 20

21 įmanoma artimiau aprašytų realiojo pasaulio objektus. Erdvinių modelių taikymas sukuria tinkamas technologines prielaidas įvairiausių techninių uždavinių sprendimui, pvz.: architektūros objektų išsaugojimas, projektavimas techniškai sudėtinguose objektuose ir pan. Per pastaruosius du dešimtmečius inžinerinėje geodezijoje labai pakito matavimo įranga. Ypač stipriai tobulėjo erdvinių duomenų kaupimo metodai taikant lazerinį skenavimą, kai įmanoma per trumpą laiką sukaupti gausią informaciją apie analizuojamą objekto formą ir jo parametrus. Skenavimo įranga sukaupia duomenis apie objektą prie jo fiziškai nesiliečiant. Lazeriniai skeneriai yra taikomi architektūros, statybos, aviacijos, transporto, kultūros, archeologijos, miškininkystės ir kitose srityse. Vienose srityse reikalaujamas aukštas matuojamų parametrų tikslumas, kai klaidos siekia iki kelių milimetrų ir net jų dalių, o kitose srityse užtenka keliolikos ar net keliasdešimt milimetrų. Norint sumažinti matavimų įrangos sisteminių ir atsitiktinių paklaidų įtaką matuojamiems dydžiams reikia atlikti matavimų įrangos kalibravimą. Darbe siekiama parengti antžeminių lazerinių skenerių kalibravimo metodiką panaudojant esamą elektroninių tolimačių kalibravimo metodiką. Taip pat disertacijoje nagrinėjami lazerinio skenavimo technologijos ypatumai, kurie iškilo eksperimentinėje darbo dalyje. Analizuojant skenavimo technologijomis sukauptus erdvinius duomenis įvertintos atsitiktinės grubios klaidos, kurios buvo eliminuotos pagal sudarytą algoritmą. Pritaikyta lazerinio skenavimo technologija kultūros objektų kartografavimui. Pasiūlytas algoritmas atviros erdvės paviršiaus modeliui, kuris papildo žemės paviršiaus (Digital Surface Model DSM) ir reljefo paviršiaus (Digital Terrain Model DTM) modelių šeimą, generuoti. Darbo aktualumas. Antžeminių lazerinių skenerių kalibravimas yra tarpinė grandis atliekant antžeminių objektų parametrų matavimus. Kalibruojant privaloma įvertinti atskirų matavimo sistemų (atstumų matavimo sistemos ir kampų matavimo sistemos) sistemingąsias ir atsitiktines paklaidas. Antžeminių lazerinių skenerių kalibravimas tikslumo prasme užtikrina kokybiškus lazerinio skenavimo duomenis žemės paviršiui modeliuoti. Tyrimų objektas. Antžeminių lazerinių skenerių kalibravimo metodika bei lazerinio skenavimo technologijų taikymai žemės paviršiui modeliuoti. Darbo tikslas. Parengti antžeminių lazerinių skenerių kalibravimo metodiką, taikant esamą elektroninių tolimačių kalibravimo metodiką, kai neturima specializuotos laboratorinės įrangos. 21

22 Darbo uždaviniai. Darbo tikslui pasiekti buvo sprendžiami šie uždaviniai: 1. Parengti antžeminių lazerinių skenerių kalibravimo metodiką taikant esamą elektroninių tolimačių kalibravimo metodiką. 2. Atlikti eksperimentinius antžeminių lazerinių skenerių kalibravimus, siekiant patikrinti parengtą antžeminių lazerinių skenerių kalibravimo metodiką. 3. Patobulinti lazerinio skenavimo technologiją žemės paviršiui modeliuoti. Tyrimų metodika. Taikyta elektroninių tolimačių atstumų matavimo sistemų kalibravimo metodika bei žemės paviršiaus modeliavimo metodai. Darbo mokslinis naujumas. Disertaciniame darbe buvo aprašyti šie matavimų inžinerijos mokslui nauji rezultatai: 1. Pasiūlyta antžeminių lazerinių skenerių kalibravimo metodika pagrįsta technologija kai atskirai kalibruojamos atstumų ir kampų matavimo sistemos. Be to, joje numatytos galimybės kalibravimą atlikti lauko sąlygomis. 2. Pasiūlytas metodas antžeminių lazerinių skenerių vertikaliųjų kampų matavimo sistemos vertikalaus skritulio skalės nulio vietos nustatymui, kuris garantuoja patikimesnius galutinius matavimo rezultatus. 3. Parengtas algoritmas lazerinio skenavimo duomenų grubioms (sisteminėms ir atsitiktinėms) klaidoms filtruoti, pagerinantis žemės paviršiaus modelių kokybę. 4. Pasiūlyta ir patikrinta technologija atviros erdvės paviršiaus modeliui, kuris papildo žemės paviršiaus modelių šeimą, sudaryti. Darbo rezultatų praktinė reikšmė. Atlikto darbo rezultatus galima pritaikyti įteisinant antžeminių lazerinių skenerių kalibravimo metodikas. Patobulinta lazerinio skenavimo technologija atviros erdvės paviršiaus modeliui sudaryti, tuo būdu papildant žemės paviršiaus modelių šeimą. Ginamieji teiginiai 1. Taikant pasiūlytą horizontalių kampų matavimo sistemos kalibravimo metodiką galima nustatyti antžeminio lazerinio skenerio horizontaliųjų ir vertikaliųjų kampų matavimo sistemingąsias paklaidas. 2. Taikant pasiūlytą vertikaliųjų kampų matavimo sistemos vertikalaus skritulio skalės nulio vietos nustatymo metodą galima nustatyti antžeminio lazerinio skenerio vertikalaus skritulio skalės nulio vietą. 22

23 3. Kalibruojant antžeminius lazerinius skenerius, būtina atskirai tirti atstumų ir kampų matavimo įrenginių sistemas. 4. Taikant pasiūlytą grubių klaidų filtravimo algoritmą galima eliminuoti matavimo duomenų grubias (sistemines ir atsitiktines) klaidas, analizuojant lazerinio skenavimo technologijomis gautus duomenis. 5. Taikant pasiūlytą algoritmą galima sukurti atviros erdvės paviršiaus modelį pagal lazerinio skenavimo technologijomis sukauptus erdvinius duomenis. Darbo apimtis Disertaciją sudaro įvadas, 3 skyriai ir rezultatų apibendrinimas. Darbo apimtis yra 117 puslapių, tekste panaudota 62 numeruotos formulės, 55 paveikslai ir 28 lentelės. Rašant disertaciją naudotasi 105 literatūros šaltiniais. Pirmasis skyrius skirtas su disertacijos tematika susijusios mokslinės literatūros analizei. Jame nagrinėjama antžeminių lazerinių skenerių konstrukciniai ypatumai bei matavimo sistemų parametrai. Identifikuotos problemos antžeminių lazerinių skenerių kalibravimo bei patikros sprendimuose Lietuvoje ir užsienio šalyse. Atlikta antžeminių lazerinių skenerių kalibravimo ir patikros norminės bazės apžvalga ir suformuluoti uždaviniai, kuriuos disertaciniame darbe tikslinga išspręsti. Remiantis išanalizuota literatūra nustatyta, kad praktiškai nesukurta metodika antžeminiams lazeriniams skeneriams kalibruoti neturint laboratorinės įrangos. Taip pat nesukurta ir metodika atskiriems antžeminio lazerinio skenerio komponentams (atstumų ir kampų matavimo sistemoms) kalibruoti neturint specialios įrangos. Skyriuje išryškinami kai kurie su žemės paviršiaus modeliavimu susiję uždaviniai, kai taikoma lazerinio skenavimo technologija. Antrame disertacijos skyriuje parengta antžeminių lazerinių skenerių kalibravimo metodika pritaikant esamą elektroninių tolimačių kalibravimo metodiką. Atlikti eksperimentiniai antžeminių lazerinių skenerių kalibravimai. Trečias skyrius skirtas lazerinio skenavimo taikymams žemės paviršiui modeliuoti. Analizuojami lazerinio skenavimo technologijų taikymai kultūros objektams kartografuoti, lazerinio skenavimo technologijomis sukauptų duomenų grubioms klaidoms šalinti, bei lazerinio skenavimo duomenų taikymai atviros erdvės paviršiui modeliuoti. Bendrosios išvados Remiantis disertaciniame darbe atliktais teoriniais ir eksperimentiniais tyrimais, gautos šios apibendrintos išvados: 23

24 1. Taikant parengtą antžeminių lazerinių skenerių kalibravimo metodiką, skenerius galima kalibruoti elektroninių tolimačių kalibravimo bazėje, neturint specialios lazerinių skenerių kalibravimui skirtos laboratorinės įrangos. 2. Pasiūlyta kalibravimo metodika patikrinta akredituotoje elektroninių tolimačių kalibravimo laboratorijoje ir nustatyta, kad metodika tinkama visiems šiuo metu geodeziniams matavimams atlikti naudojamiems antžeminiams lazeriniams skeneriams kalibruoti. Jų matavimų tikslumas siekia iki 1,5 2,0 mm ir yra žemesnis nei kalibravimo tikslumas elektroninių tolimačių kalibravimo bazėje. 3. Taikant pasiūlytą lazerinio skenavimo duomenų grubioms klaidoms nustatyti ir filtruoti algoritmą, įvertinami ledynmečio suformuoti reljefo formų ypatumai, todėl gaunamas patikimesnis duomenų rinkinys žemės paviršiui modeliuoti. Eksperimentinių tyrimų metu gauti duomenų rinkiniai, kuriuose eliminuotos visos grubios klaidos. 4. Pasiūlyta atviros erdvės koncepcija ir metodas žemės paviršiaus atviros erdvės 3D modeliui, kuriuo papildoma žemės paviršiaus modelių šeima, sudaryti. Atviros erdvės modelis skiriasi nuo kitų modelių ir naujas tuo, kad jis apibrėžiamas celės dydžiu, aprašančiu minimalius galimus laisvos erdvės tūrius, be to, jame nelieka erdvinių kliūčių. Trumpos žinios apie autorių Dominykas Šlikas 2005 metais Vilniaus Gedimino technikos universitete įgijo matavimų inžinerijos bakalauro kvalifikacinį laipsnį, o 2007 metais matavimų inžinerijos mokslo magistro laipsnį metais Vilniaus Gedimino technikos universiteto doktorantas. Stažavosi Baskų krašto universiteto Kultūros paveldo geometrinio dokumentavimo laboratorijoje Ispanijoje. Šiuo metu Vilniaus Gedimino technikos universiteto Geodezijos instituto inžinierius. Padėka Nuoširdžiai dėkoju darbo vadovui prof. dr. Eimuntui Kazimierui Paršeliūnui už suteiktus originalius mokslinius patarimus, pagalbą bei pastabas ir pasiūlymus rengiant disertaciją. Ačiū bendradarbiams, kolegoms, artimiesiems bei draugams už palaikymą supratingumą. Esu dėkingas UAB GPS partneris bei UAB Terra Modus už suteiktą galimybę atlikti eksperimentus su naujausiais antžeminiais lazeriniais skeneriais. 24