Laser Scanning Of Cultural Heritage Computer Science Essay

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Laser Scanning is the new method which introduced in the surveying industry the last decade. It has been introduced as a new unique technique for data collection and a detail recording of cultural monuments. Thus is used by engineers and archeologist to deal with the restoration or maintenance of the monuments as all the useful information is archived in the 3 dimensional object's visualization.

The use of a Terrestrial Laser Scanner is a new alternative method of surveying archeological sites. During the completion of the project, various techniques and softwares were examined.

The collected data was imported into the Leica Cyclone software that the producer recommends to use whereas they proceeded for the generation of a 3D model. Additionally a secondary software packages (Kubit) was used and examined for a further discussed and comparison. Kubit software was approved to be not reliable for prosesing all the collected data.

Finally, general reviews of the adequacy of each method are being discussed and evaluated.

Chapter 1: Introduction

1.1 History to laser scanning of cultural heritage

As the time goes by, archeology faced several problems of recording, visualizing and study of the ancient memorials. As it is well known the monuments are exposed to a permanent deformation due to the tourism and physicochemical pollution. Data recorded for archeological research has dual purposes such as; the creation of a high definition object and the virtual conversion of the archeological information which contains (K.Toth, 2009).

In order to deal with this problem archeologist used numerous techniques of recording and archiving photographs or drawings (these techniques were slow) which were displaying the objet from one visual angle by introducing optical distortion and were fading over time.

Archiving in Archaeology and History of Art faced two major problems such as the description of the object (precision) and the speed and versatility of data recording.

The documentation of cultural heritage which vary in size requires the recording of objects at close range. The irregular shapes and morphological complexity of their surfaces is a common phenomenon. The time available for measurements is mostly minor, and photogrammetry in the past was the only method that could be applied in such a tight time (A. Guarnieria, 2002) (Rogers, 2011).

However the new technologies have introduced in the surveying industry which have developed to overcome the problem of recording and viewing of our cultural treasure. The visual representation and transmission of digital information (data) is one of the most important research fields that allow all institutions dealing with culture to view the results of their work with 3D (A. Guarnieria, 2002).

Additionally an advantage can be the use and the representation of photo-realistic three-dimensional models through a virtual reality online or on optical disks can significantly help in education, the dissemination of knowledge to a wider audience and to the analysis of the damages which will help to the restoration of the monuments.

The numerous problems and obstacles that archeology faced in the past, were overcame with the introduction of the laser scanning in the industry.

Tererrestrial laser scanner (TLS) is any ground -based device that uses a laser to measure the 3D coordinates of a given region of an objects surface automatically, in a systematic pattern and at a high rate in (near) realtime. TLS is consisted form a method to collect the data (a laser scanner) and a method to manipulate the data (software solutions) (K.Toth, 2009) (SLOB).

Nowadays digitalization is a vital part of the work in archiving of cultural heritage as it provides recording capabilities for the creation of architectural, archaeological findings, historical sites and monuments of art. The prevalence of three-dimensional scanners in recent years has led to the rapidly increase of the interest in the use of 3D models in a number of archaeological studies. At the same time, the increased data speeds and editing allows the average user to have access to high quality infrastructure and displaying a large volume of 3D information. Therefore laser can be successfully being applied in archeology as an important and unique tool for three-dimensional reconstructions.

Laser scanner provides a number of advantages as well such as fast data collection of hundreds points per minute. It is cost effective for many land survey projects and it can be operated in low lighting (or at night). Most suitable and suggested method of recording historic buildings, sites and objects for reconstruction or restoration, cases that have been damaged by fires, earthquakes, floods, wars, or, as it is natural erosion. Multiple outputs from raw data (surface models, cross sections, CAD outputs) can be used for the creation of educational material for students and researchers of history and culture (Mass, 2010).

The virtual reconstruction of historical monuments and objects that no longer exist or exist only partially, the three-dimensional simulation of virtual monuments and objects with the virtual three-dimensional archaeological excavations, the analysis and remedial construction techniques can be provided as well with the laser scanning data.

Laser scanner is a fast and reliable method for surveying as it provides the most accurate and precise products than other methodology; by combining the accuracy of surveying, the completeness and conjunction of photogrammetric surveying. Less pre-processing and time working in the office are required which decrease the cost of production. Additionally it provides variable analysis in terrain depending in the required accuracies of the final product and comprehensive mapping of 3D objects without additional work or working time. However the cost of the equipment is high while the cost of surveying could be very low, as it reduces the time of recording and the number of staff needed for the recording and creation of a 3D model (K.Toth, 2009) (Rogers, 2011).

1.2 Motivations

The main motivation of this project is to the introduction of Laser Scanning in Cyprus as the new method that has brought revolution in the surveying industry worldwide and can carry various tasks with high accuracy in short period of time. The church of Agios Demetrianos was chosen as it is an ancient monument and no records exist. Laser scanner was decided to carry out the analysis of the exterior design of the church since the physical damage will continue to increase over the years. The final report and data analysis which will result from the processing will be given to the Church of Cyprus to be archived in their records for any future purpose.

1.3 Aims and Objectives

The aim of this research is to provide analysis and a detailed three dimensional model of the exterior of the church of Agios Demetrianos, located in Dali, Cyprus. This project will examine the technique of exterior design a 3d modeling and the sort of analysis that can be provided by using the most advanced and later surveying techniques introduced in the surveying industry. The methods that will be used in the data collection are the highly developed Laser scanning and GNSS receiver. It was decided to use the exterior of an ancient church in Cyprus to examine the sort of the possible provided analysis and the creation of the 3D modeling and 2D plans.

The evaluation of the laser scanning techniques will be provided in order to discuss the benefits and drawbacks that will be gained from the overall procedure. The evaluation of both, softwares and hardwares surveying techniques will comprise the time, cost, accuracy and the obstacles that surveyor was to overcome in the field.

Additionally two different objectives will be generated in this project. The main objective is to make a detailed analysis (measurements) of the geometry and the structure of the church and check which software is more suitable for such operations. Moreover the creation of 3D model will be useful information to be used for a possible restoration of the monument for any future intervention. Becoming more familiar and gain more knowledge with the laser scanning method and the appropriate softwares will give me the opportunity to explore and develop my knowledge and skills in the field that will be rabidly developed and be more essential in the surveying industry the next decade.

Chapter 2: Literature Review

2.1 Introduction to Laser Scanning

Laser scanning is a generic term for a variety of instruments which are operated for different purposes and provide variety levels of precision and accuracy. As Bohler and Marbs mentioned laser scanning is "any device that collects 3D co-ordinates of a given region of an object's surface automatically and in a systematic pattern at a high rate (hundreds or thousands of points per second) achieving the results (i.e. three-dimensional co-ordinates) in (near) real time."

In terms of Laser scanning a laser beam is emitted by the system which is reflected by the rotating mirror to the objects surfaces. Then the laser 'hits' the object and the way back to the instrument it passes through the lens and is saved to CCD memory. Laser scanning is used for terrestrial and airborne - space borne applications.

Regarding to the Terrestrial application, in TLS or ground based laser scanner the instrument should be mounted on a tripod located on known or unknown location. TLS has an integrated camera which provides colour 3D models and point clouds or to provide more visual analysis of the 3D model (Schneider and Maas, 2007).

In Terrestrial laser scanning systems (i.e. Leica C10) the laser scanning beam is classified as laser class 3R which can be used in public. A visible green laser beam is produced which is emerged by the rotating mirror. However due to the limited beam viewing the level of injured is very limited and is considered as safe (C10 manual) see figure 1.

Figure 1

C:\Users\Christodoulos Kaili\Desktop\c10.PNG

Figure shows C10 Field of View (The instrument has a rotating scan head and a rotating mirror that covers a 360° x270° field of view (FoV).

Figure 2

C:\Users\Christodoulos Kaili\Desktop\Capture.PNG

Figure: shows the classification of optical 3D measurement systems (Maas, AIRBORNE AND TERRESTRIAL LASER SCANNING , 2010)

2.2 Laser Scanning for Cultural Heritage Applications

Laser scanning has been operating in a wild range of applications in the industry. It is commonly used in:

Large structures (bridges, tunnels, dams, roads, junctions, etc.)

Urban environment (city modeling)

Mines, mining, quarrying,

Geological formations (slopes, landslides)

Archaeological (monuments, archaeological sites, excavations, sculptures, objects

Architects (facades, interiors and exteriors)

Industrial and mechanical installations and objects (factories, pylons, antennas, cabling machines, vehicles).

Positions accidents, disasters and land related to Criminology studies.

An example of the use of laser scanning for cultural heritage was the site of Chavin de Huantar, UNESCO world Heritage Site in Peru. This site is consisted by unique ruins and artifacts beginning by 1200 BCE. The natural and general hazard caused numerous disasters which influenced the site. The research was performed by the University of California at Berkely in association with Stanford University. A Leica HDS 2500 scanner was used to perform both long and close range laser techniques. An integrated control network was placed through the site for the registration of the scans (above and below ground) for the production of a 3d model. The main aim of the project was the calculation and analysis of the depth and the structural stability of the site. Scan data was also a unique tool used by the archeologist to predict the location of new perforations to prevent to the cleaning of the collapsed section of the galleries (Rocas Gallery).

Laser scanner was also used for the surveying and monitoring of Spruce Tree House, in Mesa Verde national park in North America. Spruce Tree House is a unique complex which is well known for its landscape and design. The complex which is build into a 27 meter deep and 66 meter wide recess is consisted from 130 rooms and 8 kivas. The project was performed with the aim of analyzing the implementation of the digital records techniques in order to replace the traditional survey methods used by in the site. Therefore the survey was carried out by three scanners; a Leica HDS300, Leica 2500(a long range scanning systems) and Minolta Vivid 910 (close- range scanning system). The long range scanning systems were used to for the collection of the standing architecture where the close range was used for the collection of the artifacts and wall details. However a Leica total station and a Trimble differential GPS were necessary to be used to geo-reference the point -clouds. A Nikon D70 high resolution camera was also used in the project to provide high resolution images, registered to the point cloud for the establishment of wall segments allowing the mapping of the features. The data was collected and proceed for the creation of a high resolution photograph whereas the appropriate time needed was reduced by 80 per cent by using the new techniques mentioned above (Ristevski, 2006).

A Minolta Vivid 910 scan was also used to scan the Lanzon, a 4.5 m high carved stone monolith which dataset was used for the production of spatial products, necessary for the development of an integrated plan and monitoring of the site (Ristevski, 2006).

Additionally laser scanning was mobilized for the data collection of the historic site of 'Sint-Baafs Avvey'in Belgium where there are ruins of the walls dated at seventh century AD. The document was performed in the need for a geometrically accuracy of the documents instead of the creation of 3D models for visualization for archeological sites. The task was based on the evaluation of 3D accuracies with terrestrial laser scanner and digital photogrammetric. A time of flight scanner 'Leica ScanStation2' was used to operate the first set up which was defined a scanning resolution of 3 to 4 cm. Considering the comparisons among the 3D accuracies of terrestrial laser scanning and digital photogrammetric, it was mention that the scanning resolution was not enough to reach an equal accuracy between laser scanning and digital photogrammetric. Then a phase - based laser scanner (Leica HDS6100) with a 0.5cm resolution was used to scan the wall with a range for measurement of 15 m. Additionally ScanStation2 was used to measure the point clouds, based on photographs taken by digital camera (Timothy NUTTENS, 2011). The coordinates were measured with a Trimble 8 GNSS receiver (on Real Time Kinematic) in the Belgian Lambert72 coordinate system within an accuracy of 1-2.

A non - metric Canon EOS 1Ds (11 Megapixel) high-end full-frame digital single lens reflex camera was used for the collection of photographs. These data were used for the creation of optometric images and Digital Elevation models. A reflector less total station was used for the determination of the ground control coordinates which provides us an easily orientation of the photogrammetric process, in order to georefer the orthophotos and the DEM in the Lambert 72 coordinate system. However taking in to account the control points observed by the total station a systematic error was observed both for the photogrammetric restitution and the laser scanning (Timothy NUTTENS, 2011).

Cycle of the Monts is a fresco of a global Gothic art (1250-1450), located in Buonconsiglio castle, in Trento, Italy. Due to its significant value numerous organizations such as CIRGEO, IRST and VIT were formed for the data collection and the creation of 3D modeling and realistic models by applying several surveying techniques such the image base method and the range based modeling, providing a good number of small geometric details. An Olympus E20P digital camera and a Riegl LMS- Z360 laser scanner were used for the data collection from 6 scans with a scan resolution to be obtained at mm accuracy. Leica TCR 705 total station was used to obtain the measurements of the ground control points coordinates.

A good number of texture mapping techniques were perform for the creation of geometrically accurate model. The bundle software was used to provide all the appropriate tools needed for the registration and the modeling (A. Guarnieria, 2002). Further laser scanning was also used in Oriel Chambers, world's first metal framed glass curtain walled building built in 1864, located in Liverpool. Due to the fact that no drawings were available, Z+K were produced 3D point cloud data for the creation of a 2d plan and elevation drawings. Laser scanner was the most suitable method to perform the survey as 1.8 billion points were collected from 36 scans with an overall accuracy of registration at 3mm. By applying this method high accurate data measurements were collected quick and with low cost.

LFM Viewerâ„¢ was used for the scans registrations whereas orthophoto's were used to produce Plan and Elevation drawings. (Plan and elevation update using 3D scanning )

Moreover Slob, and Hack showed that surface reconstruction is necessary for the conversion of the scanned data to 3D surface data in order to provide analysis of the shape and the character of the scanned surfaces. Reconstructed surfaces can also provide elevation contours or 2D profiles for CAD or GIS softwares.

2.2.1 Applications used of Laser scanner

Surface reconstruction techniques

In order to provide an analysis of the shape and the character of the scanned data (surface), the data must be converted into 3D surface information.

Surface reconstruction algorithm can be divided into Polygonal and parametric. For example polygonal technique is a 3D Delaunay triangulation, which provides the creation of triangular and irregular patches on the basis of linear interpolation between the points. However parametric technique can be used in areas where data is missing such as NURBS (Non-Uniform Rational B-Splines) or Fast RBF (Radial Basis Functions).

Further surface reconstruction methods are also used in 3D geological modeling (Cowan et al., 2002) for the reconstruction of large (small-scale) shapes (volumes) or for the reconstruction small (large-scale) surfaces based on dense data.

Visualization and analysis of laser scanning data

The main objective of the reconstructed surface is to allow viewing interactively scenes or objects from different directions and angles.

It can be visualized using 3D visualization techniques. Additionally in allows the user to view objects from different angles whereas shapes and surfaces characteristics i.e. roughness may be highlighted by different lighting techniques.

The reconstructed 3D surfaces generate 2D profiles or elevation contour lines which can be used in GIS or CAD software for more advance analysis.

Detailed and large - scale topographic mapping

Laser scanning can also provide fast and precise large scale detail topographic mapping.

For example it is most used in areas where the surface of the site changes rabidly due to mass movements. Laser scanning can be used to provide detailed survey. In Netherlands after the dike collapse of August 2003 in Eilnis, a detail digital terrain model was produced to represent the area including 3D characters of the contours.

Rock face surveying

3D laser scanner can provide accurate rock face surveying. Parts of the rocks which are difficult to reach can be measured, and it can determine the location of potential loose blocks for the determination of optimal stability measures. Moreover another important application is the monitoring of the movement of unstable (rock) slopes. (From: Optech, 2003).

By using laser scan surveys of discontinuous rock outcrops rock mass parameters can be determined and they can be reconstructed in a vector data format (SLOB).

Laser scanning was also used for the monitoring of a mine worked on 18th and 19th century. Due to the rough mining of stones, the mines were overburden between 2 to 6 meters. The project was performed for both stabilization of the mining and data collection in order to be achieved in their records. The survey was carried on with Photon 120 laser scanner and a Leica Total station in combination with appropriate softwares such as Pointools, Polyworks, Faro Dcene and 3D Studio Max.

Laser scanning was the only solution to carry out this survey since all the mines should be recorded in precise detail. All the data was then process to provide video journey. The animation created by Pointools was then imported into 3D studio max to provide high resolution animations (Rogers, 2011).

Further Alnwich Castle is another case that laser scanning was the best solution to carry out the procedure. Alnwich castle is one of the major castles in United Kingdom which it has been inhabitant since the 14th century. Alnwich estates performed in 2010 metric surveys which were comprised by detailed stone elevations.

In this case Scan Station 2 and Sokkia total station (reflector less EDM) was used to perform the survey and co- ordinate the castle by using the targets along the archeological site. Data was registered in Leica Cyclone software and then it was imported into Pointools View Pro for the generation of the ortho-images of each elevation. The first idea was the production of 2D elevation drawing but during the data processing in Pointools, it was decided the creation of ortho-images as it offers more advanced level of detail and accuracy. However difficulties occurred when the images couldn't fit to the point cloud as the height of the castle was increasing the photos were becoming more distorted, so the accuracy was decreasing. That was overtaken by applying to the point cloud of Pointtools a single colour. The data was processed for the creation of ortho images which were then attached in AutoCAD files and archived in Estates Departtment files (Bennett, 2011).

Further laser scanning was again the most suitable method for surveying and recording the historical structures and topographical features at Fountains Abbey, Ripon. Greenhatch Group carried out the survey with a Leica TCRP1201 (REDM) total station and Leica HDS 6200 laser scanner. 10 scans were placed along to site with minimum 11 spacing at a range of 10m for the creation of elevations and sections by the point clouds. All the control points were co-ordinated by REDM form the total station. Moreover colorized point data and panoramic photos were taken by an EOS5D camera. The targets were observed at a 3-5 mm resolution by REDM.

LSS software was used for the registration, coordination of the total station data and to export it into AutoCAD. Then Leica Cloudworx AutoCAD plug-in was used to manage the 2D data and to create segments to the point clouds to give high resolution stone by stone drawings. For the survey Total Station incorporation with a Laser Scanner were necessary to be used, in order to be achieved the highest resolution needed for the 2D cartographic drawings in AutoCAD. Laser scanning and photogrammetry was performed for the creation of stone-by-stone drawings of the walls. The data was processed for the creation of 3D triangulated Digital terrain model surface which can supplement with more detail the 2D drawings. 2D topographic drawings were created, and stone by stone drawing in Auto Cad for the English Heritage.

In the case of Dounray castle (a unique archeological site in Scotlant is well known for its L- shaped footprint) laser scanner was the only way to survey and record the building safety as the building was in a bad condition and it was not allowed entrance within 10 m of the structure for health and safety reasons. A grid of 8-10 mm was set as it was collected a sufficient amount of data and information from the stones. 2D elevation drawings were produced (Macleod, 2010).

Shedding light on the history of glass hall

The Heidelberg Castle is one of the most beautiful and visited archeological sites in Germany. It is well known for its unique renaissance style and it dates from 13th century. On 18th century a good number of damages occurred. Therefore for the reconstruction of the monument it was decided to be created a detailed drawing of the castle which will included the static constructive loss.

However the scanned plan was digitized in Auto CAD software. Photo plans which were produced from the walls were designed as foundation for the building restoration analysis. The visualization was organized and processed with MonuMap in Auto CAD software figure3. MonuMap software was used to connect all the collected information into a single plan, and then multiple thematic maps were generated for more advanced process and analysis (Dr. Claudia Mohn).

Figure 3

C:\Users\Christodoulos Kaili\Desktop\CAD_heritage_documentation.jpg

2.3 Distance Measurements with Lasers scanning device

2.3.1 Time of flight Method

Time pulse it is most common method ,used for medium and long range scanning for large objects and outdoor applications. It provides a medim accuracy of 5 mm for a single point and medium spatial resolution to a mm level. This laser emits a laser beam onto the rotation mirror and then reflects it to the direction of the desired scanning area. The lasers 'hits' the object and on the way back it almost follow the same direction as it is includes some error in time and wavelenght. The measurements are saved on a CCD memory.

C=299792458 m.s (speed of light in a vacuum)

n=1 : correction factor

Ï„= time of flight

΄΄If the light waves travel in the air then a correction factor equal to the refrective index, which depends on the air temperature, pressure and humidity m must be applied to c, n=1.000285΄΄

Figure 3

C:\Users\Christodoulos Kaili\Desktop\laser.PNG

Figure: Measurement using a time of flight or a phase-comparison measurement system. (English Heritage)

2.3.2 Phase Based Method

Phase based technique is a high rate process of data capture which can capture up to 1 million points per second. By using a continous wave laser the range is measured as phase offset between outgoing and return signal. It is most suited for medium and large objects as it provides a medium accuracy of up to 5 mm for a single point, precision less than 2mm and a high spatial resolution of mm level. It is used for medium to long ranges of 2-3 m (English Heritage).

2.3.3 Triangulation Method

Moreover TLS triangulation or optical triangulation , offers a high accuracy less than 1 mm and is most comonly used in close range measuremnets of 2-3 m for small features and objects. In the triangulation method the laser beam is emitted by the system and is reflected by the rotating mirror to the objects surface. Then the laser 'hits'the object and on the way back to the instrument it passes through the lens and it is saved into CCD memory. (Shan, Toth, 2009).

Figure 4

C:\Users\Christodoulos Kaili\Desktop\Capture.PNG

Figure 4: A schematic of a mirror based triangulation measurement system. (English Heritage)

2.4Laser scanning types and comparison

For the wide range of applications a good number of laser scanning systems are operated in the industries which have individually chosen to achieve the best and most accurate data for specific applications.

Firstly Trimble manufacturing has a wide range of laser scanning systems such as the Trimble FX 3D Scanner, the Trimble CX, Trimble FX, and Trimble VX Spatial Station. The Trimble manufacturer provides instruments which can capture up to 216.000 points per second with a 360*270 field of view. However each instrument has designed for individual applications. For example the Trimble FX 3D Scanner with a range up to 80 m is most commonly used for industrial facilities for updating plant documents, civil engineering i.e. capture 3D data, for inspection and for surveying applications. It is connected via a Wi-Fi connection from a touch screen or laptop device in order to operate (Limited, 3D Laser Scanning , 2010).

However the Trimble TX5 is used in the application fields for surveying, BIM, Industrial facilities, Inspection/ Reverse Engineering, Tunneling and Crime Scene (Limited, 3D Laser Scanning , 2012).

It is consisted by a camera and a touch screen for monitoring of the data. It can provide measurement speed from 122000 up to 976000 points per second with a range from 0.6 m up to 120 m and with field of vies 300 *360 with a ranging error from +- 2mm at 10 m and 25m each at 90% (Systems, 2012).

Trimble Cx is a wave pulse laser scanner which combines time of flight and phase shift. It has the ability to capture of 50000 points per second with a FOV 360 *300. It is operated in a range of 80m to 90% and a reflective surface with a single point accuracy of 4.5 mm at 30m and 7.3mm at 50m respectively. It is most commonly operated for industrial facilities, oil storage tanks, surveying, inspection/reverse engineering, crime scene & Forensic and BIM (Limited, Trimble 3D Laser Scanning, 2011).

Leica Scan Station C10 is the first laser scanning system which can be used for all the applications in the industry. It is a pulsed laser scanning with a dual axis compensated. With a video camera and a Smart X Mirror, it can capture up to 50000 points per second within a range of 300 m and with full field of view 360 *270. Additionally it provides to the users the ability to traverse and use targets for the best and more efficient data collection for interior and exterior applications. Additionally it can allow georeference, register and check the collected data faster. A position accuracy of 6 mm and distance accuracy of 4mm is provided in applications used (Plant &Marine, Building / Heritage Civil, Forensics). Additionally it's compatible with Leica GPS smart antenna by providing accurate position data without the using GPS or total station by reducing the time in the field. (AG, Leica ScanStation C10).

Leica P20 Scan Station is the new version of Leica Scan Station C10 which provides more accurate and precise data collection. This instrument has the capability to 'Check and adjust 'in order to check and adjust itself for a maximum level of performance. It is consisted by a class 2 laser and it is operated in a temperature between -20°C to +50°C. It is compatible with a GNSS SMART ANTENNA. High speed pulsed laser scanner, auto adjusting, integrated high resolution digital camera and laser plummet, 3D position accuracy of 3mm at 50 m, and 6 mm at 100m. It can be operated between sunlight until complete darkness. With a Field of view 360 *270 and an integrated 5 mega pixel it can provide video capabilities (AG, Leica ScanStation P2).

Finally Topcon GLS-1500 Laser scanner is a pulse laser scanner which collects up to 30000 points per second with a 4mm precision up to 150m. It can provide precise measurement at a range of 500m. It is consisted by an integrated camera of 2.0 megapixels, class 1 eye safe laser, dual axis compensation and stand alone operation. However a pc is needed in order to check the data that has been collected during the survey. It is commonly used for monitoring antenna, building, and earth. It occupies a known coordinate and therefore it can traverse and locate other points by using its back sight capabilities

Manu-facturer

Feature

Range

techno-

logy

Wave-

length

{nm}

Min

/Max.

Range

Range

Accuracy

@50m {mm}

Field

of view

Scan

Speed

{Points/s}

Weight

{kg}

Software

Faro

FARO

FOCUS 3D

0.6/120

Up to 976000

5

Topocon

GLS-1500

Pulsed

500 m at 90%, 223 m at 18%

3"

360*70

30,000

17.6

Trimble

FX3D

Phase

685nm

2.4

360*270

216.000

11

TX5

905

2/25

4mm

300*360

976000

5

CX

TOF-Phase

660nm

80m at 90% 50 at 18%

7mm

360*300

54000

11.8

Leica

C10

Pulsed

532 nm

300 m @ 90%;

134 m @ 18%

4.5mm

360*270

50000

13

Cyclone

Table 2 : Overview of Terrestrial Laser Scanner Manufactures and features

(Phase = Phase based , TOF Time of Flight )

2.5 Atmospheric effects affecting the measurements and the results

The first thing that has to be taking into consideration before starting the process of analysis or modeling of the cloud points is the noise detection which is operated by the Leica Cyclone software.

Noises generally are points resulting due to the continuous passage of pedestrian, and vehicles. Additionally the laser scanning system as it ''captures everything that see'' has the ability to capture points that do not belong to the area of interesting and will cause errors during the modeling process by complicating the procedure (Ingensand, 2006).

Noise generally has to be deleted after the registration of the station as they affect the measurements and the visualization of the point clouds. Additionally Cyclone software provides a wide range of tools which simplify the management of the point cloud. The points are reflected in colour which provides to the user a friendly environment in identification of the objects. These options help to the user to see the objects from deferent angles and then by using the fence mode may remove those points ''Noise'' which are not part of the surface node.

2.6 Registration Methods

The registration procedure in TLS (Terrestrial Laser scanner) involves the function of the conversion to the entire point cloud and the evaluation of the registration parameters. The union of the point cloud is the procedure performed to integrate the original point cloud resulted from each scan station, into a single point cloud that includes full coverage of the scans including all the data collected in the field. For the union of the point cloud it is necessary to be selected the same points between each scans building on the overlapping area in order to improve the accuracy of the point cloud.

2.6.1 Target based registration

Target based registration is the case where a precise point correspondences among an existing coordinate system. This is achieved by placing targets in the area of interest within the laser scanners field of view. Then registration is achieved by oversampled the geometric primitive or planar targets. (Maas, Airborne and Terrestrial laser scanning , 2010).

2.6.2 Iterative closest point methods

Cloud to cloud registration uses cloud registration by using point cloud overlap. This overlap between the scans can also leads to a wider and more precise data resolution and accuracy (Maas, AIRBORNE AND TERRESTRIAL LASER SCANNING , 2010).

2.7 3D analysis of laser scanning data

The methodology in each operation varies according to the type of application that is investigating in each case, the object, the precision requirements that is aimed to be achieved, and the desired outputs. Therefore in order to plan a scan; a proper selection of the appropriate equipment should be taken into consideration and the technique that is going to be used, the analysis that is going to be provided and the positions and locations that are going to be placed for the scan.

Laser scanning systems provide a wide range of analysis such as alignments, georeferencing the clouds for the production of the final point cloud. Performance characteristics for the creation of 3D plans, maps, sections, facades and modeling for the production of Digital Terrain Model can also be provided. Various tools for examination and analysis such as measurements, calculations of area or volume, comparisons between them and then the final product to produce a comparative visualization and complex reports of the accuracies and precisions of the operation.

2.8 Modeling National Heritage Monuments

For the creation of a 3D modeling of a scene or an object and in order to examine the sort of analysis, a good number of softwares packages are available in the market. However in this project it was decided to be used Leica Cyclone, Kubit Point Cloud & Point Sense Heritage and AutoCAD. In Leica Cyclone software the 3D modeling of the national heritage is going to be produced based on the laser scanner data collected by the scanner. Leica Cyclone software is the main software for registration of the point cloud data and 3d modeling.

Kubit Point Cloud and Point Sense Heritage are two softwares which are processing laser scanning data within the AutoCAD software environment by providing its own tools for modeling and further data processing. (Soumagne)

Auto Cad software is the main software used almost from all the sectors of engineering in the industry as it supports 2D and 3D draftings. By providing the traditional method of data acquiring in 2D elevation drawings as it is most commonly used by architects or engineers and by generating 3D viewing of the model; allows the user to represent the model that it has been created.

Chapter 3 methodology

3.1 Techniques

In order to be operated a surveying project numerous techniques may be used for the best and more accurate results.

3.2. Reconnaissance

In the surveying industry and in the engineering sites an action plan is essential item to be generated, as it provides useful information about what it has to be carried out and how the procedure will be operated on time. Therefore during the first visit in the archeological site, it was decided to examine the area, create a 2D plan and carry out the required measurements of the distances with tape.

Further control stations were set up where the coordinates were collected by using a GNSS receiver and finally the Laser Scanner was set up for data collection.

Firstly before the operation of the project, an analysis of the area was provided by using Google earth maps. Then by taking into account the major factors for a surveying project such as the line of sight and the distances between each station, 4 stations were formed in the control network since the church was not big enough.

Data Processing

-Noise elimination and filtering

-Alignment of all acquired scans in a unique reference frame

-Global points cloud

SURVEY

-Choose of the surveying equipment

- Plan and design of the procedure

-Number and location

-setting up of targets

-Carrying out the survey

However a GNSS receiver was decided to be used in ordnance survey national grid for data collection of the two stations coordinates (station 1 and 4), as the ordnance survey reference point located in the area was in a long distance from the area of interest.

RESULTS

-Creation of sections, plans

-Analysis of the points cloud data

-3D modeling generation

3.3 Laser scanning observation

The Laser Scanning method was operated by using the Leica C10 Scan Station. Overall, 7,263,926 points were collected for the exterior of the church. A loop traverse procedure was followed by using the laser scanner.

However in order to be achieved it was necessary to take into consideration the two known coordinates which were collected by the GNSS receiver; station 1 (E: 239487.971, N: 378519.718, H: 223.208) and station 4 (E: 239464.821, N:378528.810, H: 223.131). Therefore the laser scanning system was first set up into station 1 where the two targets where placed to station 4 which was used as a reference point and at station 2 respectively. As Laser Scanning system is operated in the same way as a total station, the traditional surveying methods of Face left and Face right was decided to be carried. The unknown point (station 2) was re-coordinated by the laser scanning system by calculating the coordinates of the two known stations (1&4) respectively. Then the same method was used to carry on the whole traverse. Finally the loop traverse method was finished by setting up the laser scanner station at station 4 and observing to station 1 and station 3 respectively. During the above procedure the laser scanning system was taken multiple scans around the Field of View of each control station in the network in order create a cloud of points which can be used for further data analysis or for the creation of the 3D image of the area of interest (Field Techniques Manual: GIS, GPS and Remote Sensing ).

.C:\Users\Christodoulos Kaili\Desktop\target station.PNGTarget over a known point

Station set up at a known point

C:\Users\B0864938\Desktop\photo.bmp

3.4 Terrestrial Laser Scanning Data

As it was mentioned above terrestrial laser scanners may be consider as extremely automatic total station. In the case of total station, the operator choose directly the points be measured, whereas laser scanner acquire a set of points 'cloud' randomly around the Field of View of each control station in the network. The user has the user has the ability to select the area of the object that has been investigating and the density of points that is required. As these values are chosen the data acquisition is automated completed in a short period of time. Therefore a density set of points are result which generate a Dense Digital Surface Model (DDSM) (L.Bornac).

3.5 Data Processing

3.5.1. Data analysis

Moreover in order to be proceeded the Laser scanner; two main actions should be taken into consideration. The main action is the pre- treatment of the data and the solid modeling of the density point cloud.

Pre- treatment is the number of procedures carried out before the final procedure which is the modeling of the point cloud. It is consisted by the georeferencing operations, the noise reduction (data filtering) and the point cloud registration.

The second and final action of the laser scanner data is the creation of 3D modeling which can be created by the use of point cloud (L.Bornac).

3.5.2 Measurements

Cyclone like other available design softwares provides a wide range of available tools for data processing. Measurements between the objects surfaces might be easily calculating by selecting 2 point using the pick mode tool. All the measurements are saved, copied and viewed to the Windows clipboard.

3.5.3 Alignments

Survey with alignments is the method which may accelerate the procedure of processing the million of points which are represented in the cyclone software. Therefore alignments, cross sections may be created so they may be easily represented.

Alignments can be easily created by selecting two points into the surface of the object, one at the start and one at the end of near to the center. Moreover alignments may be represented by the combination of the curves and polylines.

3.5.4 Cross sections

Cross sections are usually created by using the alignments and the command tools ''Alignment section- Create section'' by entering the preferred spacing. However alignments and cross sections may also be generated by selecting with the pick mode two points one at the start and one at the end. Therefore the parameters may be selected by each station set which are based on the highest and lowest points.

3.5.5 Exclusion Volume

Exclusion volume can be created by selecting the group objects which are replaced by a rectangular object.

3.4 Ortho image

Point sense heritage software (Kubit software) was the best available software in the market that it could be used for the creation of ortho images in the AutoCAD environment. By using the appropriate available commands and tools, 4 ortho images were produced from the point cloud data (Figure 3). Basically ortho images are projections parallel into a plane. They are not ortho images as they do not use photos basis of the colour but they use only the colour represented by the point cloud data. Ortho image is also unique tool for point cloud data digitization as it can be displayed into a 2D AutoCAD software environment that does not carry point cloud data capabilities yet.

However an important factor that it has to be taken into consideration for the creation of an ortho image is the resolution, the point size, its position and the x-ray. In this case the resolution for units per pixel was set at 4 whereas x-ray percentage at 0%. As a result a true colour image was generated representing four images from each station of the network.

C:\Users\Christodoulos Kaili\Desktop\Stage 3\Dissertation\images from laser scanner\Autocad-kubit\Orthoimages\orthoimage3.bmp

Figure 3

3.5 Modeling

3D modeling was decided to be created as it is a realistic representation of the existing features surrounding the church, based on their coordinates.

3.5.1 3D Modeling in Cyclone Software

Leica cyclone is the most popular and advanced available software in the market in terms of data processing and 3D modeling generation of the point cloud data. 23,920,705 points were imported in Cyclone which was aimed to create a 3D model. Modeling might be generating by choosing the area of interesting and then by using the appropriate commands such as region grow- patch which creates patches. Generally these plane surfaces are created by the average calculation of points located in the chosen area and their size might be changed as the user preferred. Additionally Kubit ''Point Cloud Pro'' can be also used within AutoCAD tools.

3.6 2D Architectural Plans

As it is well known AutoCAD is the most common used software in the engineering industry. Ortho images were imported in AutoCAD in conjunction with the measurements taken by the Cyclone software, 2D plans were generated. 2D architectural plan are generally the major and most important documents for the direct rebuilding of the monument. Information such as floor plans, elevations, site and sections were generated with detailed measurements.

Chapter 4: Analysis- Results

4.1 Evaluation of Products

As it was mentioned above, four software packages were used for the point cloud data processing of the church. In the section below the techniques that were used will be represented and compared. Additionally the benefits and the drawbacks regarding to the final product will be reported.

4.2 Evaluation of the Techniques

Firstly Leica Cyclone software was used for point cloud data pre- processing and processing. The registration of the stations was achieved and then by applying its unique techniques such as noise reduction all the redundant data were removed for a better visualization of the monument. Additionally measurements of the walls and the existing features surrounding the monuments were taken. Moreover Cyclone was the dominant software for data processing as it was the only way to export the data into Ascii and Pcg formats in order to be imported into Kubit and AutoCAD softwares respectively.

Secondly the data was imported into the Point Sense Heritage software where Ortho Images were generated and then quite few measurements were achieved to be taken for a later discussion.

Finally 2D plans were generated in AutoCAD by processing the Ortho Images which were created by Point Sense software. Figure 4 shows the final product documentation as it is most commonly requested by the specialist in the construction industry. C:\Users\Christodoulos Kaili\Desktop\autocad drawing.PNG

Figure 4

4.2.1 Comparison of Software

Data processing was operated over a period of 5 months, including the modeling time, ortho images generation and 2d drawings. Additionally each from the above softwares has its own properties and tools that differ from other. For example cyclone is the only software which was used and could register the data and removed the errors. The tools and commands that are provided make the 3D modeling procedure easier and is more users friendly. However due to the fact 7,263,926 points were processed in the software, these caused the software to be overloaded. Therefore the overall procedure lasted more time than the approximate time as the points were overloaded every time that it was aimed to process the data.

Kubit software provided the approximate results ''ortho images '' that were aimed to be provided. As the number of points which were imported into Point Sense Heritage were decreased rapidly, the data was then processed faster than cyclone.

However the 3D building point cloud visualization was not represented very well, as a good number of points were rapidly decreased during their exportation from the Cyclone software. Therefore features as doors, windows or roof couldn't be recognized easily.

Further 2D drawings were produced in short period of time. Due to the fact that AutoCAD processed only ortho images, the operation was achieved easily with more accurate and specified measurements.

4.2.2 Comparison of Time

The two known stations were observed by a Leica GNSS receiver. As a Laser scanning data collection was operated within 6 hours from a network of 4 stations. Usually in Laser scanning operations the time required for each data collection depends on the instruments specifications and the appropriate data resolutions which are recommended from English Heritage. Regarding to that Leica Scan Station C10 was used to document a full scan operation 360*270 with the resolution to be set up to high definition. However the new scan station P20 introduced by Leica Geosystems has the ability to capture up to one million points per second in ultra high speed.

4.2.3 Comparison of Accuracy

As Phlipsen in 2006 mentioned the required accuracy of each survey depends in the basis of each surveying technique that is used. The accuracy is always affected from the beginning of the survey until the last processing part. In this case, the measurements were affected from the observation of the stations as some errors like multipath affected the measurements. Additionally accuracy is still affected in the processing part as the 4 scan words must be joined together for the creation and representation of the 3D point cloud. Each software offers its own abilities and potentials. Regarding to the table (figure 5) 2D measurements taken by the 2D plans are closer to the traditional method of surveying (tape measurements) as Auto Cad drawings are more accurate as they were created from the Ortho Images.

However comparing the measurements between the 2 softwares which were used for the point cloud data processing we can see the difference between the measurements. This is due to the fact that the measurements were taken by separated points in the point cloud. Generally the error in the measurements differs only some centimeters.

Measurements

Leica Cyclone

Kubit software

2D plans

Tape

Floor plan (door)

8.948

9.039

8.9630

Floor plan

9.118

8.886

9.0490

Front (plan)

5.344

5.5952

5.3440

Back (right)

0.704

0.7319

0.7705

0.75

Back (left)

0.748

0.7940

0.8090

0.80

Door

1.1290

window

0.286

0.2798

0.2798

Figure 5

4.2.4 Comparison of Effort and Costing

Laser scanning system as it is well known, records large amount of point cloud data precisely and accurately in a short period of time. For example after setting up the laser scanning system and the targets, the data collection was achieved in short period of time due to the high speed data collection provided by the instrument. Additionally labor costs are quite few as the procedure requires only one person for the collection of data.

However due to the large amount of recorded data, quite few days are required in the office for the data to be processed. The data processing requires special treatment to remove the unnecessary information whereas the data collected from the field can only be exported after the processing. The software package usages, requires experience for visualization and processing as it is not used by all the professionals in the industry.

Like each service everything has its own price. The Leica Scan Station C10 that was used for the operation of the survey including the tripods and the prism costs about to £100,000.

In the other hand another documentation and data recording can be achieved by the used of total station as well. Total station as it is well known collects single points with the use of a reflector prism where 2 people are required. For that reason in some cases such as 3D modeling without specific requirements, as precise and accurate representation of the surrounded features may be generating by processing the data collected by the Total Station. This 3D visualization of the building may be achieved easier as the data processing will be easier as the user observes only the points required. Therefore the overall processing will be achieved easier as fewer points will be processed faster. A Total station including the tripods and prisms costs about £10000.

Chapter 5: Discussion

In this chapter, the problems, difficulties and facts that would be avoided will be examined and further discussed.

5.1 Problems, Difficulties and Facts to be avoided

The field operation was achieved in a small period of time. However a good number of problems and difficulties were occurred during the data processing.

Due to the fact that the Leica cyclone software used for importing the data was upgraded, the registration process was achieved automatically. Therefore during the attempts, of the manual registration by using the Iterative closest point method the software noted 'Registration Failure' as the constraints were insufficient. After a time consuming process of selecting more constraints, the software processing was operated very slow due to the huge amount of the processed data by obtaining the results of RMS 0.016 cm, Average 0.009 and max 0.098 which were unacceptable.

Moreover a long time was spent in exploring the possible sort of analysis that can be provided by Leica Cyclone software. Results were not as expected as a good number of commands were unavailable with the point cloud data. Regarding to figure 6 surfaces calculation couldn't be achieved with the point cloud data. Additionally neither the volume calculation nor the angle measurement or exclusion volume couldn't be estimated. C:\Users\Christodoulos Kaili\Desktop\error in measurement of surface with point clouds.JPG

Figure 6

However as it is represented in Figure 6 all the commands became available only after modeling the building. Cross section couldn't be used as useful information for further data analysis as they were not created in straight sections as they were generated manually by selected points in the point cloud (Figure 7). Further due to the limit space of the storage the modeling procedure couldn't be finished neither the creation of the mesh modeling.

C:\Users\Christodoulos Kaili\Desktop\commands come available only with modeling.png

Figure 6

C:\Users\Christodoulos Kaili\Desktop\cyclone cross sections.JPG

Figure7

Kubit Point Sense Heritage and Point Cloud was investigated for a possible further analysis that can be provided. In this case the size of the points was changed for a better representation of the feature. Additionally Point clouds sections were created (Figure 8) in order to be loaded for a further interpolation. However during the exportation of the data from Cyclone a lot of points were eliminated.

Due to the elimination of the data, lack of data was occurred and a good number of features as doors, or friezes were not distinguished well (Figure 9). Therefore modeling couldn't be achieved. Moreover following the instructions of the manuals analysis for the surfaces of the walls or the rock formation surrounded the church couldn't be achieved as photogrammetric properties were appropriated.

C:\Users\Christodoulos Kaili\Desktop\Stage 3\Dissertation\images from laser scanner\Autocad-kubit\sections - multiple slices\define slice ( lower part ).PNG

Figure 8

C:\Users\Christodoulos Kaili\Desktop\lack of data.PNG

Figure 9

Chapter 6: Building Information Modeling

Laser scanning has introduced new unique surveying techniques in Building information modeling which offer real time -up to date building data conditions. It produces point clouds surveys which can be used to provide building analysis and details of existing building geometry. Then this data can be imported into Building Information modeling software which can process the data and then it can be used for a further renovation or it can be used to show up deviations from the building geometry. (Chuck Eastman, 2011)

Chapter 7: Conclusion- Recommendations

In Chapter 7 the completion of objectives and aims set in Chapter 1 are going to be discussed, with the skills that have been gained during the completion of the project.

In the first chapter the objectives and aims of the project have been discussed. Data was processed using both software packages, and the surveying techniques were compared concerning costing, accuracy and time effort and the software comparison. Knowledge and experience has been gained during the field operation and the data processing allowing the operator to be more familiar with the laser scanning technique the appropriate softwares. Further the relevance of the techniques that have been discussed and a good number of the objectives have been achieved.

Softwares analysis and 2D architectural elevation plans were generated as a final documentation for a future reconstruction of the monument. The overall procedure was achieved starting from the collection of data using the GNSS receiver, collecting of data using the laser scanner, software analysis and finally 2D architectural plans.

Regarding to the results and the knowledge gained during the process, the main purpose of the project was the examination of the laser scanning methods with suitable softwares available in the market.

Cyclone software is the main software for data processing collected from the laser scanner as it is used for the registration of the stations for the generation of the monument. However by examineding the tools available in the software it was demonstrated that tools were not available with the point cloud data, but only after the modeling process. Moreover due to the memory limitations meshes and the modeling couldn't be finished as the software became very slow and couldn't process the data.

Further during the second attempt for examination and analysis with the Kubit software, the data exported by cyclone for importing in Kubit software was altered. Therefore due to the point reduction the 3D modeling was incomplete and not realistic whereas the only sort of analysis which could be provided was the 3D modeling and the ortho images.

Ortho images which were produced were proved to be very useful information as they were imported in Auto Cad for the generation of the 2D architectural plans.

Concluding i would like to mention that from the overall analysis and examination of the terrestrial laser scanning techniques (hardwares and softwares) and taking into consideration the cost of the productions that in the case of the generation of simple 3D models or 2D drawings its most recommended the used of the Total Station. By using the total station the operator has the ability to collect only essential points instead of the thousands points collected by the laser scanner. Therefore the procedure will complete in shorter period of time.

In the other hand operator has always to take into considerations what has been requested by the client as the total station may offer faster and cheaper 3D modeling and Auto Cad drawings representation, whereas Terrestrial Laser Scanning provides the overall realistic and sufficient representation of the area investigated.

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