Terrestrial laser scanners (TLS) adalah penderia tanpa-sentuh, peralatan yang berasaskan optik yang mencerap data tiga dimensi (3D) bagi permukaan objek yang ditakrifkan secara automatik dan sistematik dengan kadar cerapan data yang tinggi. Kemampuan ini menyebabkan TLS digunakan secara meluas bagi pelbagai aplikasi 3D. dengan kemampuan untuk menyediakan data 3D yang padat, TLS telah menambah baik fasa pemprossesan untuk menghasilkan model penuh 3D, yang lebih mudah dan cepat. Pra- pemprosessan merupakan salah satu fasa yang terlibat, yang terdiri daripada prosedur pendaftaran dan georeferencing. Disebabkan oleh sumber selisih yang banyak didalam cerapan TLS, maka, pra- pemprosessan bole dianggap sebagai fasa yang sangat penting untuk mengenalpasti kehadiran selisih dan unsur luar. Kewujudan selisih di dalam fasa ini mampu mengurangkan kualiti produk akhir TLS. Dengan tujuan untuk membincangkan isu ini, kajian ini telah melaksanakan dua eksperimen, yang melibatkan cerapan data bagi pemantauan tanah runtuh dan topografi 3D. Dengan melaksanakan kedua-dua kaedah pra-pemprossesan secara langsung dan tidak langsung, hasil yang diperoleh menunjukkan bahawa TLS sesuai digunapakai untuk aplikasi yang memerlukan ketepatan pada tahap sentimeter.
Despite the breadth of topics involving TLS, there has been a large-scale absence of scientific inquiry into the specific ways police utilize TLS technology during crime scene investigations. This is surprising: after all, the above-mentioned experiments are undertaken in the name of forensic literature, which necessarily exists because of policing. If researchers are interested in applying TLS as police do (i.e., in forensic contexts), they should be cognizant of any standards or best practices. For example, TPS investigators typically place reference targets – normally in the form of white spheres or small, paper checker patterns – within the crime scene environment when using TLS. The purpose of this is to ensure accurate registration, the process wherein individual scans are stitched together into one cohesive body. Notwithstanding, some scanners, including the Focus 3D , can perform accurate, automatic registration without targets. This is made possible through computer software with the ability to automatically recognize geometric planes in the environment. Ultimately, as long as there is sufficient overlap within separate point clouds, whether targets or natural geometric features, the software can easily register disparate scans into one cohesive point cloud. The targets prove most useful when there are no easily recognized geometric planes, which may be the case in outdoor scenes. The use of targets should be considered a fail-safe and a police best practice, especially in environments lacking distinctive geometric features.
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Urban Environments are becoming increasingly more populated which is causing a change in society’s lifestyles, modes of transport and ways of living into more vertical forms. This is resulting in the transcending of the cadastre from traditional and historic 2D land parcels into 3D spaces to which are attached complex rights, restrictions and responsibilities. Often the visualisation of these 3D spaces is unclear using archaic two mediums such as survey plans. Given the capability of terrestrial laser scanners to deliver information rich point clouds and 3D datasets, the aim of this dissertation is to investigate the feasibility of using a terrestrial laser scanner to visualise a 3D cadastre.
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obtained results. Close proximity of water envi- ronment creates local micro-climatic conditions, which not always foster observations with the ex- pected accuracy. Surveying instruments that meet the high expectations (high density of the ob- served points, accuracy, speed, economics) can be found among terrestrial laser scanners. Terrestrial laser scanners allow for the registration of mil- lions of points representing the surveyed surface. XYZ coordinates and the laser beam’s inten- sity value in particular places are obtained as a result of a survey. Owing to the point clouds registered during a scan, quasi-linear point mod- els of a concrete dam can be created. Using those models as a base, it is possible to perform various geodetic analyses and acquire data for detailed analytical and computational considerations [Popielski et al., 2007].
Recently, emergence of new surveying equipment (such as terrestrial laser scanners (TLS)) stimulated development of new methods suitable for soil erosion assessment. New capabilities allow remote evaluation of arable land with highest accuracy (fraction of a mm) and, inaccessible to traditional techniques, density of data points (millions of measurement points). It is important to keep in mind that TLS techniques have a number of practical advantages: high data acquisition speed without precision loss; fully digitized model of an object; data acquisition independent of lighting conditions; access to remote and complex objects; full automation of the measurement process; measurements of geometric parameters using digital 3D-model; data storage in a digital form; multiple use of laser scanned results.
Garcia (2013) completed a geometric calibration of a TLS. LASEGIFLE software used for additional parameters (AP) modelling. The Methodology Garcia used was a reference network of point targets and spheres. Redundant measurements of these targets were collected with the TLS setup at different positions. This was a very good paper, with a good explanation of the calculation process. Hanke & Grussenmeyer & Grimm-Pitzinger & Weinold (2008) calibrated the Trimble GX which superseded the Mensi, using direct georefrencing. The GX had an active dual-axis compensator that corrects the horizontal and vertical angles during the scanning. Some of the findings were two scanners can have different additive constants. All the data measured by the scanner was not available , only distances. Abbas (2013) completed a self calibration on the Faro Photon 120 scanner. Abbas used seven scan stations, statistical analysis (t- test) showed all error models, the constant , collimation axis, the trunnion axis and the vertical circle index error in his findings.
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Abstract: This article presents a methodology to process information from a Terrestrial Laser Scanner (TLS) from three dimensions (3D) to two dimensions (2D), and to two dimensions with a color value (2.5D), as a tool to document and analyze heritage buildings. Principally focused on the loss of material in stone, this study aims at creating an evaluation method for loss control, taking into account the state of conservation of the building in terms of restoration, from studying the pathologies, to their identification and delimitation. A case study on the Cathedral of the Seu Vella de Lleida was completed, examining the details of the stone surfaces. This cathedral was affected by military use, periods of abandonment, and periodic restorations.
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Before commencing laser scanning, investigation of the subject area was conducted to determine number of scans needed to fulfil project objectives as well as position of individual scans. The scan positions needs to ensure that blind spots are minimized and to ensure that point coverage is at maximum. Another element that needs to be taken into the consideration when planning the positions of the scans is equipment limitation. Faro Focus 3D laser scanner will be used and spheres will be used as artificial targets. Limiting factor of the Faro Focus 3D is the range at what scanner can identify spheres and that range is around 15 metres. Consequence is that scan positions could only be 30 metres apart. Taking all this into account 15 scanning positions were roughly determined. Furthermore, artificial targets, spheres, must be carefully positioned with good geometry and with different elevations around scanner to ensure good usability later on in registration process. Figure 3.5 shows fifteen positions from which the scans will be conducted.
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Terrestrial laser scanners (TLS) are used nowadays as Geomatics instruments for various applications. One of these applications is 3D survey and management of oil and gas facilities and other engineering structures. This recent attention is due to the fact that laser scanner has the ability to generate massive amounts of high resolution 3D coordinated cloud points from the surface of the structure. A structure may be scanned from several locations and when these scans are registered together, they will provide complete surface coverage. This paper outlines the use of laser scanner as applied in the determination of the verticality of Reservoir Engineering Structure. The results reveal that the Reservoir did not exceed the allowable tolerance.
The HDS4500 measures distances up to 53m, while the HDS3000 and the ILRIS can measure up to 100m and 1500m, respectively. Due to the limited speed of 1500 or 4000 points per second and due to the limited field of view it quickly became clear that the ILRIS scanners and the HDS 3000 are not useful for the busy and narrow streets of the project area. These scanners are more suitable for the documentation of landmarks. Thus, all buildings were scanned with a scan resolution of ~15mm at the object using four HDS4500. For data processing of the scanned point clouds, which includes registration, geo-referencing and segmentation of the point clouds, five licenses of Cyclone 5.2 and four licenses of Polyworks 4.1 were used in the office.
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Since 2005, the Aknes rockslide has been investi- ˚ gated and monitored as part of the ˚ Aknes/Tafjord Project (www.aknes-tafjord.no). It is one of the biggest landslide monitoring projects in the world employing a multitude of geological, structural, geophysical and borehole investiga- tions (Blikra et al., 2006a; Blikra, 2008; Ganerød et al., 2008; Roth and Blikra, 2009). The monitoring focuses not only on the measurement of slope movements using a large variety of techniques (Kveldsvik et al., 2006), but also in- cludes measurements of meteorological, seismic and ground- water conditions (Blikra et al., 2006a; Blikra, 2008; Roth and Blikra, 2009). Some displacement monitoring techniques are point based (GPS, extensometers, total station, and laser dis- tance meters), while others are area based (photogrammetry, satellite-based and ground-based radar interferometry, aerial laser scanning (ALS), and TLS). Point based measurements
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The remote sensing tool employed in this study is a TLS. This instrument is also known as a Ground based LIDAR (Light Detection and Ranging system). We used an ILRIS-3- D model (Intelligent Laser Ranging and Imaging System), from the Optech™ 2004–2006 series. Although this is a well- known technique (see some examples of application in Abell´an et al., 2006; Oppikofer et al., 2008; Pesci et al., 2009, etc.), its basic principles are discussed as follows. The instrument mainly consists of a transmitter/receiver of infrared laser pulses and a scanning device (internal system of rotating mirrors). The laser beam is directly reflected by the land surface, obviating the need for intermediate prism reflectors. TLS shows a relatively very high data acquisition speed (up to 10 000 points s −1 ) compared with conventional surveying methods (e.g. total stations); more specifically, the ILRIS-3-D model is able to acquire up to 2500 points s −1 . Range measurement (ρ) can be undertaken using first or last pulse of the return signal; the last pulse is the optimal choice to obtain the return signal of the rock face (in place of vegetation). The distance to an object is calculated using the Time-Of-Flight (TOF) of the laser pulse (Eq. 1):
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To conclude, terrestrial laser scanning point cloud data was used to develop a 3D model of engineering structures, which are the outcome complete with the dimensional measurement and 3D point cloud data to support the construction industry. TLS enables more efficient 3D data acquisition in the field of civil infrastructure compared with conventional techniques (Son et al., 2015).
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Twelve checkerboard targets (Figure 1) were used as common points and placed throughout a mock scene. The total station occupied a location such that all of the checkerboard targets were in view and it did not interfere with the laser scanning process. Traversing is the act of occupying a new location to increase range or collect currently obstructed data. Traversing the total station tends to introduce small amounts of error and this was avoided by placing the targets in locations which were all visible to the total station within a single setup . A traverse was also avoided with the understanding that many crime or collision scenes can potentially be surveyed with one occupy location. A fixed back sight was established using a -30 mm offset prism on a prism pole and bipod. The backsight was placed in the scene among the checkerboard targets, just over 20 m to the east of the total station. This backsight was the first point collected and was collected again at the end of the survey to display any error in the total station and its operation.
The laser scanner used in this letter was a Riegl LMZ210i, which uses a two-axis beam-scanning mechanism and a pulsed time-of-flight laser range finder to measure the 3-D position of points within a range of about 350 m. Line scan measurements are produced through the rotation of a polygon mirror and frame scan measurements through the rotation of the optical head of the scanner. The angular step width in both line and frame scan directions may be set by the user to determine the angular separation between laser shots. The line and frame scan angle ranges may also be determined by the user within the limits of the instrument (Table I). Data may be recorded as either first return or last return, or a combination of both.
Currently, laser scanning has become a supplementary technique for geodetic applications. The use of laser scanners is constantly growing. There are different laser scanners available from different companies (Schulz et al. 2004) the arrival of a high accuracy terrestrial laser scanner means that the inspector/surveyor can be in a safer location, away from high speed traffic and obtain huge amounts of detailed data rapidly and cost efficiently (Garry, 2007).
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Data of object surface for reverse engineering can be captured either from contact or non- contact method. Laser scanning (non-contact method) usually gives high accuracy of captured data, however it also produces high point density. The difficulty of processing million of points captured by laser scanning device is the main problem to generate useful surface model. Data reduction process should be performed to reduce the number of points while maintaining the accuracy. This paper evaluated data reduction procedures on point cloud from laser scanner device. The procedures comprise of noise filtering, filter redundancy and point sampling method. Each procedure was tested using two types of sample models (freeform and primitive). The results show that the combination of filtering methods help to reduce the amount of original point cloud while maintaining the detail of surface.
Occlusion in TLS data is inherently incorporated into the gap probability approach. In geometrical modelling, occlusion generally needs to be overcome by merging scans recorded at multiple locations with a trade-off between sampling time and scan resolution/number. The efficiency and value of this ap- proach would be increased if occlusion could be overcome in a way that is more efficient both in the field and during data processing. Mobile scanners provide one prospect for such an efficient measurement. Mobile scanners generally incorporate one or multiple single-axis scanners that are mounted on a vehicle, and a review of such systems is provided by Petrie and Toth . While limited demon- stration has been reported , the accessibility difficulties in forests for scanners mounted on a stable vehicle plat- form have limited their widespread use. An alternative to mobile scanning are handheld systems like the Zebedee [80•], which uses automatic feature recognition to contin- ually track the origin of the scanner. Bosse et al. [80•] refer to this as simultaneous localisation and mapping (SLAM). The system has been tested in forest environ- ments with some preliminary assessment of the results relative to conventional TLS .
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Abstract During the last decades, documentation of buildings has proven to be a valuable tool for a variety of civil engineering issues, such as urban planning, preservation and restoration of cultural heritage buildings, as well as monitoring during the construction phase. Several techniques have been developed for this purpose including topographic, photogrammetric and ground-based remote sensing techniques or a combination of them. The increasing interest in the generation of 3D facade models for documentation of built environment has made laser scanning a valuable tool for 3D data collection. Regarding civil engineering, terrestrial laser scanning could be considered an efficient method for digitizing buildings facades, generating dense 3D point clouds available for further processing. This paper presents the study of a mansion house of cultural significance built in the middle of the 18th century, using terrestrial laser scanning techniques for facade documentation. Scanning process included multiple external scans of the main facade of the building which were registered using artificial targets and appropriate software to form a single colored 3D model. Further process resulted in a model that offers measurement possibilities valuable to future plans and designs for preservation and restoration. High resolution satellite data were also used to gain detailed information about the physiognomy of building’s surrounding area.
which affects the amount of dead wood (Yrttimaa et al. 2019). Natural phenomena, such as insect damage, the spread of pathogens, wind damage, and forest fires, shape forests at different spatial and temporal scales. Insect damage, that is often combined with the spread of pathogenic fungi, causes defoliation and changes in the bark whereas winds fell trees or tree parts (Saarinen et al. 2016) and fire burns low vegetation, needle mass and possibly also reshapes the structure of trees (Gupta et al. 2015, Carvajal-Ramírez et al. 2019). Wind damage is abrupt, forest fire may last for weeks, and insect damage is often spread widely in space and may last over several years (Vastaranta et al. 2012, Korovin 1996, Junttila et al. 2019). The temporal distribution of these damage events is usually unpredictable and the spatial scale varies from single trees to landscapes. There are also abiotic changes that affect the forest structure. These include land-use changes, silvicultural and harvesting operations. Considering the applicable area for close-range sensing, land-use changes are not included in this review. In managed forests, trees are often planted, seedlings are tended, and several thinning operations are carried out during the rotation period (Holopainen et al. 2014). Silvicultural practices vary a great deal, but in general, a proportion of trees is typically removed in silvicultural and harvesting operations (Liang et al. 2012). The spatial distribution of silvicultural events at the landscape-level can be characterized somewhat unpredictable as the temporal distribution is cyclic (White et al. 2018). At the level of a forest stand and a tree, changes caused by forest operations can be seen as abrupt changes that take place within a few days. Thus, spatiotemporal information is needed to improve the understanding of, or quantify, the consequences of these natural phenomena, processes, and human activities with varying temporal and spatial patterns and dimensions. Close-range sensing technologies, such as terrestrial laser scanning (TLS), mobile laser scanning (MLS) and the use of unmanned aerial vehicles (UAVs) are included in our review as they are mainly used for the collection of detailed information from single trees, forest patches or small forested landscapes.