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... generating a polygonal or polyhedral mesh in the form of a 3D grid that approximates a geometric domain. Various algorithms exist for this purpose such as the polygon mesh and Delaunay triangulation =-=[38]-=-. Depending on specific application needs two types of mesh models can be considered. Firstly, regular type mesh models which constitute a mathematical representation of the surface in question, and s...

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...trary, close range photogrammetry can provide image-based 3D models of a tunnel tube. Such models are produced using multiple images of an area suitably corrected for lens and perspective distortions =-=[10]-=-. For this purpose various processing techniques exist, ranging from stereoscopic vision of pair images to multi-convergent analysis supported by bundle adjustment. Nevertheless, although photogrammet...

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... in many cases, under rough field conditions. Their use in the underground space environment is suited to a wide spectrum of application areas, ranging from civil engineering [1,12], to cave modeling =-=[13]-=- and archaeological documentation [10]. Section 3 provides a summary of current use of TLS in tunneling applications. From this review it is evident that despite the rapid expansion of TLS in tunnelin...

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... Besides, geometry documentation is of particular importance both to the contractor and the design engineers, and thus, it has a great impact on the technical as well as economic aspects of a project =-=[1,2]-=-. Traditionally, the surveying tasks relating to tunnel excavation operations have primarily relied on conventional surveying methods and to a lesser extent on photogrammetric techniques [3–7]. In the...

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...es to the distance measurement technique that a TLS system employ. According to this sorting approach three principal methods exist, known as, triangulation, interferometry and time-of-flight methods =-=[19,20]-=-. The first technique operates on the basis of optical triangulation; that is, a light source (i.e., a single laser spot or a laser stripe) scans an object surface while its reflection is being record...

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...1253 pattern that, if analyzed appropriately, can lead to the measured distance. However, this approach is suited only for short, ultra-precise (sub-millimeter) distance and displacement measurements =-=[17]-=-. Most TLS systems used for engineering geodesy applications employ the time-of-flight method [14,17]. In this case, two operating principles for distance measurement are in use: the pulsed time-of-fl...

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...ttes and vertical reference points. Also, integrated systems employing motorized laser and gyro-theodolite technologies are used to establish and maintain directional alignment of the excavation axis =-=[4]-=-. Laser scanners are generally not suited for setting-out operations. However, just a few of the latest models render simple setting-out functions, e.g., the Leica Geosystems, ScanStation 2. A compreh...

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...es to the distance measurement technique that a TLS system employ. According to this sorting approach three principal methods exist, known as, triangulation, interferometry and time-of-flight methods =-=[19,20]-=-. The first technique operates on the basis of optical triangulation; that is, a light source (i.e., a single laser spot or a laser stripe) scans an object surface while its reflection is being record...

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...racy in a short time and, in many cases, under rough field conditions. Their use in the underground space environment is suited to a wide spectrum of application areas, ranging from civil engineering =-=[1,12]-=-, to cave modeling [13] and archaeological documentation [10]. Section 3 provides a summary of current use of TLS in tunneling applications. From this review it is evident that despite the rapid expan...

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...and positional information and can be used for detailed inspection of the tunnel body and for documentation of its equipment. Also, they provide base data suitable for planning refurbishment projects =-=[25]-=-. Usually, for this type of surveys kinematic laser scanners are used, whereas, scanning of the excavation face and profile control checks is undertaken using static laser scanning systems. The main a...

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...try documentation operations aiming at profile and volume computations. In the first case, a longitudinal spacing between instrument setups that equals the tunnel diameter would suffice most projects =-=[27]-=-. This spacing offset can be substantially increased if ordinary profile or volume computations are required. As a result, an increase in the spacing between instrument setups will lead in overly fast...

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... scans together, to form a continuous 3D scan image. For this purpose, a technique known as “fuzzy joint” is used to compute the optimal adjustment transformation parameters between neighboring scans =-=[36,37]-=-. The working principle of this technique resides on minimization of the root mean square (RMS) error of the residual distances involved for all points lying within the overlap zone. However, it shoul...

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...is usually the most appropriate option. Depending on the type of use, TLS can be operated either from a static position (mounted on a tripod) or from a dynamic platform (attached on a moving vehicle) =-=[14,15]-=-. In the first case, the TLS is used to produce a detailed map of the topographic features of the area around the static location that is occupied by the scanner, whereas in kinematic mode, it facilit...

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...is usually the most appropriate option. Depending on the type of use, TLS can be operated either from a static position (mounted on a tripod) or from a dynamic platform (attached on a moving vehicle) =-=[14,15]-=-. In the first case, the TLS is used to produce a detailed map of the topographic features of the area around the static location that is occupied by the scanner, whereas in kinematic mode, it facilit...

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... scans together, to form a continuous 3D scan image. For this purpose, a technique known as “fuzzy joint” is used to compute the optimal adjustment transformation parameters between neighboring scans =-=[36,37]-=-. The working principle of this technique resides on minimization of the root mean square (RMS) error of the residual distances involved for all points lying within the overlap zone. However, it shoul...

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... Besides, geometry documentation is of particular importance both to the contractor and the design engineers, and thus, it has a great impact on the technical as well as economic aspects of a project =-=[1,2]-=-. Traditionally, the surveying tasks relating to tunnel excavation operations have primarily relied on conventional surveying methods and to a lesser extent on photogrammetric techniques [3–7]. In the...

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...heless, although photogrammetric techniques offer a universal and relatively low-cost alternative, their use is less common in tunnel works due to the uneven wall surface and poor lighting conditions =-=[11]-=-. Also, despite the rapid advances on software tools that facilitate data collection and the processing cycle, stereoscopic plotting still requires expertise operators [10]. In recent years, the emerg...

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.... Horizontal geodetic control on ground surface is usually undertaken by means of satellite geodesy (GPS observations), while vertical control points are established using precise leveling techniques =-=[21]-=-. Subsequently, ground surface networks are densified and stretched out to provide geodetic control for tunnel excavation. For this purpose open (zig-zag) or loop (polygon) traverses are established t...

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...ological/ggeotechnical documenttation of thhe rock sur rface. Howwever, this topic is no ot elaborateed thhereinafter in study and the intterested reaader is refe erred to coonsult Deckker and Do ove =-=[26]-=- annd Fekete et al. [27]. Figure 7. Raw TLS intensitty data (a) and digital image; (b) obtained at tunnel Tem mpi T1 face immmediately after blastinng and excaavation mat terial removval; Laser innten...

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...ation at two stages following the beginning of the excavation cycle; firstly, immediately after blasting and removal of the excavation material, and secondly, after a shotcrete layer has been applied =-=[39]-=-. Figure 6 shows the observation setup of the scanner and the sphere targets used for data geo-referencing. To ensure safe operation conditions and the best possible observation geometry, the scanner ...

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...tively, tunnel surveying can rely on laser scanning technology. This section provides comparison results of all three techniques based on sample data obtained from Tempi T1 and N. Ikonio case studies =-=[40]-=-. For the case of the Tempi T1 tunnel the TCRM 1101 Plus spatial station was used to manually measure profiles at intervals 1.5 m over a tunnel portion 50 m long, collecting points every 1 m on each s...

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... routinely geometry checks relating to assembling and locating the form in space, it was deemed necessary to check the formwork for deviations in the nominal geometry of the precast metallic segments =-=[41]-=-.Sensors 2012, 12 11266 Figure 14. View of the formwork from the north portal abutment. The location of TLS stationing in the south abutment is denoted by a circle (a); The raw point cloud data recor...