Tóm tắt luận án tiếng anh: Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.

Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.Nghiên cứu công nghệ quét laser mặt đất trong lĩnh vực địa hình và phi địa hình ở Việt Nam.

HANOI UNIVERSITY OF MINING AND GEOLOGY

CUONG SY NGO

RESEARCH ON TERRESTRIAL LASER SCANNING TECHNOLOGY IN TERRAIN AND NON-TERRAIN FIELDS IN VIETNAM

Major: GEOMATICS AND MAPPING ENGINEERING

Code: 9.52.05.03

SUMMARY OF THE PHD THESIS

HANOI, 2022

Remote Sensing, Faculty of Geomatics and Land Administration,

Hanoi University of Mining and Geology

Supervisor

Assoc Prof Dr Truong Xuan Tran,

Hanoi University of Mining and Geology

Reviewer 1: Prof Dr Quy Ngoc Bui Reviewer 2: Prof Dr Hung Le Trinh Reviewer 3: Dr Khang Du Nguyen

The thesis will be defended at the University-level thesis evaluationcommittee at Hanoi University of Mining and Geology, at 8.30 amon 2022

The thesis can be found at theses libraries: The Hanoi National Library or The library of Hanoi University of

Mining and Geology

1 Rationale of the study

Nowadays, in the field of ground space data collection, theintegration of Global Positioning System (GPS), digital imagetechnology and laser technology for data exchanges via the Internet

is a trend The typical one is the laser scanning system Thescientific, complete and systematic research in order to bring 3DTerrestrial Laser Scanning (TLS) technology in the fields of terrainand non-terrain is the interest of scientists, researchers and managers

Therefore, the PhD thesis’s topic ‘Research on Terrestrial Laser Scanning technology in terrain and non-terrain fields in Vietnam’

was selected based on the scientific and practical significance

2 Research aims and tasks

2.1 Aims: To establish a scientific basis and methodology for

building ancillary programs in Terrestrial Laser Scanning dataprocessing To building 3D TLS technological processes for severalnon-terrain objects

2.2 Tasks: Research on a theoretical basis of 3D TLS technology

and error sources affecting the accuracy; research the algorithms anddevelop a program to process the 3D TLS data; experiment to verifythe research results

3 Objects and scope of the study

3.1 Objects of the study: The Digital Topographic Models (DTM) of

the areas with diverse topography was established, and the accuracywas assessed In terms of the non-terrain field, the 3D models ofcaves, landscape streets and historical and cultural relics were built,then modeling for the socioeconomic development

3.2 Scope of the study: The terrain objects are the areas of Gia Phu

village in Binh Duong commune, Gia Binh district; and the Lim hill

of Lim town in Tien Du district, Bac Ninh province Non-terrainobjects are the Dau Go cave in Ha Long Bay, Quang Ninh province;

the Ta Hien and Dinh Liet old streets in Hoan Kiem district, Hanoicapital; the Buu Long pagoda in Ho Chi Minh city; and someantiques of the But Thap pagoda in Bac Ninh province.

4 Research methods

Statistical method; analysis and synthesis methods; modelingmethod; and experimental method

5 Scientific and practical significance of the thesis

5.1 Scientific significance: Building and completing in a

synchronous and scientific way the theoretical basis of 3D TLStechnology Proposing the solutions, technological processes, and theauxiliary programs for the application of 3D TLS in the geospatialdata collection and processing The purpose then is for building theDTM and a number of non-terrain applications in the actualconditions of our country

5.2 Practical significance:

The 3D TLS was brought into play the advantages in maximizeautomation of data collection and processing to meet thetechnical, quality and cost requirements The point filteringprogram was introduced and successfully applied in processingthe 3D TLS data in accordance with practical conditions in ourcountry Then, these results will contribute to promote theapplications of new technologies and to serve the goal ofmodernizing the cartography field

6 Defense points

Defense point 1: Using the scanning data filtering algorithm with the

addition of surface modeling, developing a TIN model andenhancing the filters in order to build an ancillary program This oneallows automating point cloud data processing, ensuring the quality

as well as the efficiency in the DTM establishment

Defense point 2: Proposing the 3D TLS technological process for

building 3D models for different non-terrain objects synchronously

It ensures the technical requirements of the accuracy to meet thesocioeconomic development requirements in Vietnam.

7 New points of the thesis

- Building the ancillary program in 3D TLS data processing based onthe scanning data filtering algorithm with the addition of surfacemodeling, developing a TIN model and enhancing the filters It willhelp to accurately represent the DTM accordance with currentrequirements in Vietnam

- Proposing the 3D TLS technological process for building 3Dmodels for different non-terrain objects

8 Thesis structure and content

Introduction: An overview of the thesis, the rationale, aims,

significance, and literature review in local country and in the worldrelated to the content of the thesis From there, the research methodsand the content are formed At the same time, the defense points andthe new points of the thesis are given

The main research contents of the thesis concludes four chapters:

Chapter 1: Overview of literature review of 3D Terrestrial Laser

Scanning Technology in the terrain and non-terrain fields

Chapter 2: Scientific basis and error sources affecting the results of

Terrestrial Laser Scanning

Chapter 3: The program establishment to process the 3D Terrestrial

Laser Scanning data in the terrain field

Chapter 4: Process establishment of 3D Terrestrial Laser Scanning

for surveying several non-terrain objects

Conclusion and recommendation part: Summarizing the research

parts in the thesis and giving the conclusions affirming the researchresults on the point cloud data processing filtering by TLS.Proposing the 3D TLS technological process for surveying eachspecific non-terrain object

Chapter 1 OVERVIEW OF LITERATURE REVIEW OF 3D

TERRESTRIAL LASER SCANNING TECHNOLOGY IN THE

TERRAIN AND NON-TERRAIN FIELDS

Within the scope of this thesis, the author only focuses on research

of the 3D TLS technology Laser technology was conceived anddeveloped in the 1960s by the scientist namely Theodore H Maiman

It is based on the basis of the theory of Charles Hard Towner andAsthur Leonard Schawlow [76]

Literature review of the 3D TLS studies

1 Literature review in the world

The application of the 3D TLS technology in terrain and non-terrainfields has been concerned by many researchers around the world,mainly in the field of non-terrain applications

1 Research and applications in terrain field: There are a number of

researchers such as Nora Tilly, Peter Schürch, Andri Baltensweiler,etc [30,31]

2 Research and applications in non-terrain field: In the research of

Glenn J Newnham, Francesco Pirotti, Mathieu Dassot, MohammedOludare Idrees, Soohee Han and Yusuf Arayici[12,13,14,27,35,36,40]

3 Research and application of point filtering algorithms: Scientists

have done including L.Monika Moskal and Guang Zheng [18],J.Susaki [39]

4 Research and commercial software development: such as

TRIMBLE [72], LEICA [73], RIEGL [74], FARO [75]

In addition, the problems of the TLS accuracy is also concerned bymany scientists around the world For example, author group J.-Angelo Beraldin, François Blais, Uwe Lohr [16], or group of authorsBalzani, M., Pellegrinelli, A., Perfetti, N., Uccelli, F [10]

In general, the problems of current TLS technology are quite complete.However, in these studies, the authors only focused on scientificinformation They did not give any specific technological processes anddid not analyze the detailed algorithms These references are only basicinformation, mainly focusing on specific applications, and often quitefragmented, difficult to absorb and implement.

2 Literature review in Vietnam

The applications of 3D TLS in the terrain and non-terrain fields arequite cared by scientists in our country In 2020, the author NguyenViet Nghia established a coal mine map with the high accuracy usingthe TLS technology In 2019, the Ministry of Natural Resources andEnvironment issued Circular 17/2019/TT-BTNMT namely

"Technical regulations for establishing DEM by ground-basedLiDAR scanning technology on fixed stations"

In 2017, the author Tran Quoc Vinh researched combining data ofdrones and TLS in order to create the 3D maps of urban areas [7] In

2015, the author Vu Quoc Lap chaired the topic namely "Researchand application of TLS technology to improve the geospatial dataquality , then to strengthen the state management capacity in mineralactivities" [4] The application of TLS technology to terrain and non-terrain purposes is not new in our country, but it is still notsystematic

Sub-conclusions of Chapter 1

In this chapter, the author has stated the reasons for choosing the 3D TLS technology for terrain and non-terrain applications This is the new technology in Vietnam following the trend of 4.0 technology revolution.

This chapter was presented some applications of the 3D TLS technology in terrain and non-terrain fields It was also presented the literature review using TLS technology in the world and in Vietnam There are only some research and applications in the field

of terrain in our country currently, and the applications in the field of non-terrain is still limited From there, the author draws out the remaining problems that will be solved in the thesis.

Chapter 2 SCIENTIFIC BASIS AND ERROR SOURCES AFFECTING THE RESULTS OF TERRESTRIAL LASER SCANNING 2.1 Working principles of terrestrial laser scanning system

-transmission to the computer; 5 - dedicated computer.

Figure 2.3 Coordinate system of TLS stations [20]

2.1.2 Working principle of the long measuring block of the TLS equipment

1 Determination of distance length by pulse measurement “Time of flight”

Figure 2.4 Principle of pulse measurement to determine distance

length [59]

2 Determination of distance length by phase measurement “Phase based”

Figure 2.5 Diagram to determine distance length by phase

measurement [55]

3 Determination of distance by laser scanning triangulation method

Figure 2.6 Distance determination by laser scanning

triangulation method [52]

2.1.3.Working principle of TLS equipment rotary block

1 Working mode of step rotation of TLS equipment

Figure 2.7 Principle of angle positioning step [52]

2 Working mode of continuous rotation of TLS equipment

Figure 2.8 Principle of the continuous angle positioning [52]

2.2 Error sources affecting TLS results

2.2.1.Classification of TLS errors

All errors in TLS can be divided into two groups:

1 Equipment errors are caused by the quality of manufacturing,assembling and adjusting optical, mechanical and electronic parts ofscanning equipment They include as follows: working stability ofTLS equipment; working accuracy of long measuring block; errors

of angle blocks These errors are shown in the profile of the scanningdevice during the manufacturing, assembly process, and areperiodically checked

2 Method errors that the measurands themselves are determined byTLS equipment Methodological errors caused by the surrounding

environment when doing the laser scanning; Methodological errorsare caused by the characteristics of the scanned objects Moreover,there are also errors during the coordinate transformation, errors indata conversion.

2.2.2 Methodological errors of TLS

1 Surrounding environmental effects when TLS:

The influence of factors includes atmosphere, refraction, attenuatingelectromagnetic waves, device vibration, etc To determine therefractive index of electromagnetic waves taking into accountmeteorological data when scanning objects, the formula [61] can beused:

𝑛 = 1 + 𝑛 55𝐸𝐺−1 𝑃 - x 10−9 (2.19)

𝑅 1+ 𝛼 (𝑇+273,16) 760 1+ 𝛼 (𝑇+273,16)

where, α - the gas constant và equal to 1/273.16;

P - the atmospheric pressure, measured in mm of mercurycolumn;

E - the absolute humidity of the air, unit of measure

gram/m3;

T - the air temperature, unit of measure Kelvin;

nG - the atmospheric standard refractive index calculated according to the formula [61]:

2 Errors caused by the characteristics of the scanned objects:

The influence on the TLS results shows that the basic properties ofthe scanning objects are shape and reflectivity, which are determined

by the material composition and color The influence of themeasuring objects on the accuracy of received spatial information,which mainly appears about the errors of the measuring distances.The process of transmitting laser pulses into space is verycomplicated

The input signal function has the following general form:

𝐹 (t)

=∫∆𝜑 ∫∆𝜐 [𝐹 (𝑡 − 2𝐷 (𝜑,𝜐)

)𝐾

(𝜑, 𝜐) 𝜓 (𝜑, 𝜐)]d𝜑 D𝜐 +𝑜𝑢

𝑡 −∆𝜑 −∆𝜐 𝑟𝑎 ��

η(t) (2.23)

𝑟𝑒𝑓

where, Fout (t) – the output signal function;

D (φ, υ) – the function describing the change from the laser

emitted source to different points of the object (reflecting the shape

When doing the TLS, it is necessary to determine the characteristics

of the TLS stations, including: maximum vertical and horizontalscanning resolutions; laser radiation wave length; edge, vertical andhorizontal measurement accuracy; dispersion of the laser beam

4 Errors in data reference conversion

The errors are related to the data acquisition and feedback of scanrays from objects to refer to the geodetic reference system Theseinfluencing factors will be described in details on data quality [25]

5 Errors in data format conversion

Point cloud data usually has standard formats such as: e57, ptx, pts,fls, lfc, etc Each scanner manufacturer creates its own standardformat If the third-party users want to use the data, they mustperform a conversion process This is also an important point duringthe data processing and exchange

Sub-conclusions of Chapter 2

TLS technology operates on the foundation of science and technology and information technology development It affirms its superiority compared with other traditional technologies It contributes to strengthening and modernizing the surveying, mapping and geographic information fields The research content of this chapter contributes to supplementing and perfecting a number of issues on the theoretical basis of TLS for teaching, scientific research as well as pratical applications in our country.

Through analyzing and evaluating the error sources affecting the TLS results, it is found that the errors in the coordinate conversion process has a large and systematic influence on the accuracy of the point cloud Then, it is considered as a basis for providing solutions

to handle requirements of collected quality data and to choose the suitable equipment when performing different work purposes.

The data obtained from the TLS is large and diverse There is a need

to build an auxiliary program allowing the automation of point cloud data processing and the model quality assurance for terrain and non-terrain aims This issue is addressed in the next chapter.

Chapter 3 THE PROGRAM ESTABLISHMENT TO PROCESS THE 3D TERRESTRIAL LASER SCANNING DATA

IN THE TERRAIN FIELD 3.1 Filtering algorithm from point cloud data to build DEM

To classify land surface and non-land surface layers, there are manyfiltering algorithms to optimize automation in the point filteringprocess This algorithm is grouped according to 3 basic criteriaswhich are [35]:

 Slope - topography

 Geo morphological model

 Land cover

Developing TIN models and enhancing the filters

Parameter estimation using statistic analysis

Finding the center points of the ground objects

Creating preliminary data structure, DTM Center points of the ground objects

Surface Modeling