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Statement of problem The anatomic complexity of the ear challenges conventional maxillofacial prosthetic rehabilitation. The introduction of specialized scanning hardware integrated into computer-aided design and computer-aided manufacturing (CAD-CAM) workflows has mitigated these challenges. Currently, the scanning hardware required for digital data acquisition is expensive and not readily available for prosthodontists in developing regions. Purpose The purpose of this virtual analysis study was to compare the accuracy and precision of 3-dimensional (3D) ear models generated by scanning gypsum casts with a smartphone camera and a desktop laser scanner. Material and methods Six ear casts were fabricated from green dental gypsum and scanned with a laser scanner. The resultant 3D models were exported as standard tessellation language (STL) files. A stereophotogrammetry system was fabricated by using a motorized turntable and an automated microcontroller photograph capturing interface. A total of 48 images were captured from 2 angles on the arc (20 degrees and 40 degrees from the base of the turntable) with an image overlap of 15 degrees, controlled by a stepper motor. Ear 1 was placed on the turntable and captured 5 times with smartphone 1 and tested for precision. Then, ears 1 to 6 were scanned once with a laser scanner and with smartphones 1 and 2. The images were converted into 3D casts and compared for accuracy against their laser scanned counterparts for surface area, volume, interpoint mismatches, and spatial overlap. Acceptability thresholds were set at 0.70 for spatial overlap. Results The test for smartphone precision in comparison with that of the laser scanner showed a difference in surface area of 774.22 ±295.27 mm2 (6.9% less area) and in volume of 4228.60 ±2276.89 mm3 (13.4% more volume). Both acceptability thresholds were also met. The test for accuracy among smartphones 1, 2, and the laser scanner showed no statistically significant differences (P>.05) in all 4 parameters among the groups while also meeting both acceptability thresholds. Conclusions Smartphone cameras used to capture 48 overlapping gypsum cast ear images in a controlled environment generated 3D models parametrically similar to those produced by standard laser scanners.

A 3D laser scanning strategy based on cascaded deep neural network is proposed for the scanning system converted from 2D Lidar with a pitching motion device. The strategy is aimed at moving target detection and monitoring. Combining the device characteristics, the strategy first proposes a cascaded deep neural network, which inputs 2D point cloud, color image and pitching angle. The outputs are target distance and speed classification. And the cross-entropy loss function of network is modified by using focal loss and uniform distribution to improve the recognition accuracy. Then a pitching range and speed model are proposed to determine pitching motion parameters. Finally, the adaptive scanning is realized by integral separate speed PID. The experimental results show that the accuracies of the improved network target detection box, distance and speed classification are 90.17%, 96.87% and 96.97%, respectively. The average speed error of the improved PID is 0.4239°/s, and the average strategy execution time is 0.1521 s. The range and speed model can effectively reduce the collection of useless information and the deformation of the target point cloud. Conclusively, the experimental of overall scanning strategy show that it can improve target point cloud integrity and density while ensuring the capture of target.

The high corrosion resistance, low density, and useful biological activity with heat resistance of titanium alloys have made them the most outstanding choice in various industrial applications. However, their poor tribological properties inhibit utilizing them in applications that need abrasive and adhesive wear resistance. Laser cladding is being applied to increase the capabilities of such alloys by allowing the deposition of different hard coating materials. This paper attempts to study the thermal, microstructure, and clad layer geometry evolution during coaxial laser cladding of Ti6Al4V titanium alloy with tungsten carbide + nickel-based alloy preblended powder. Owing to the difficulty in experimentally measuring the thermal and microstructure evolution due to lots of laser processing parameters, a new three-dimensional numerical model based on finite-difference analysis for studying the entire process has been proposed. The behavior of the different thermophysical properties of WC, NiCrBSiC, and Ti6Al4V materials, as well as the phase transition based on latent heat and fluid dynamics considering materials velocity, viscosity, and buoyancy force, during melting and resolidification processes, were considered to improve and ensure the accuracy of the numerical model. The proposed model could be applied to accurately estimate the temperature history and the deposited clad layer morphology and geometry. The cooling rate and thermal gradient were investigated to predict the solidification rate and microstructure by using different laser cladding parameters. It was confirmed that the laser power has a substantial impact on the peak temperature in the melt-pool, while the laser scanning speed has a significant effect on the heating and cooling rates. In conclusion, the process parameters have to be carefully chosen to certify a good quality clad layer with the preservation of the WC particles.

Fabrication of the surface micro-texture on the C-plane sapphire is undertaken by a 355 nm Ultraviolet (UV) pulsed laser. The surface micro textures of sapphire with different laser scanning line spacing ranging from 10 μm to 100 μm are obtained, where the selection range of scanning line spacing is controlled in the range of the groove width and plasma width to obtain a surface of high Peak-Valley (PV) value. A reasonable processing order is proposed to manufacture different types of surface micro-textures on sapphire by laser ablation trajectory regulation. In the multiple-passes laser ablation of sapphire by the UV nanosecond pulsed laser, the scanning lines in each direction is treated as once scanning. On this basis, the multiple processing can be carried out to avoid the influence of the subsequent scanning on the machined groove. In addition, the effect of different scanning line spacing on the PV value is quantified and different types of surface micro-textures on sapphire, including the squares, the rhombuses and the hexagons, are successfully fabricated, which can be applied in the friction reduction or anti-reflection field.

Ti6Al4V is one of the most widely used titanium alloys due to its excellent mechanical, physical, and chemical properties. Laser surface texturing is a promising method to endow new functions of material surfaces; however, direct generation of laser-induced periodic surface structure (LIPSS) on the Ti6Al4V surface by nanosecond laser is rarely reported. In this study, by nanosecond laser irradiation in nitrogen atmosphere, the ripples (a typical LIPSS) were directly fabricated on the Ti6Al4V surface. By single-line laser scanning, the effects of laser irradiation parameters including the laser power and repetition frequency on the formation and evolution of the ripples were systematically investigated, followed by optimizing the laser irradiation parameters to achieve the large-area regular and clear ripples with relatively good surface quality as well. Furthermore, by performing contrast experiments in argon atmosphere, the role of nitrogen atmosphere on the formation of ripples was confirmed. Accordingly, formation mechanism of the ripples was discussed. Finally, the effects of the formed ripples on the surface color and wettability were preliminarily characterized to demonstrate the potential applications of surface ripples. This paper provides a nitrogen assisted method to fabricate large-area ripples on the Ti6Al4V surface by nanosecond laser irradiation.

Fabrication of thin-wall components using the laser powder bed fusion (LPBF) additive manufacturing (AM) technology was investigated for two “hard-to-weld” high gamma prime Ni-based superalloys RENE 65 (R65) and RENE 108 (R108). Simple block parts with wall thicknesses of 0.25 mm, 1.00 mm, and 5.00 mm are printed using a bidirectional laser scanning strategy without layer-wise rotation. Parts with walls thinner than 5 mm fail before reaching the designated build height. Results indicate that reduction of limiting build height (LBH) corresponds to the reduction of part thickness and is unaffected by alloy composition. On the contrary, the number of internal micro-cracks along columnar grain boundaries in the build direction (BD) increases with part thickness and is significantly higher in R108 than R65. These findings suggest that reduced LBH in parts with thinner walls is not caused by internal micro-crack formation. Fractography and finite element analysis (FEA) of the in-process thermal stresses show that the LBH trend is not explained by the conventional cracking mechanism. Simulations suggest that part thickness affects stress distribution leading to more substantial distortion and consequent failure to add layers for continued fabrication of thinner parts.

Laser-induced controllable oxidation coupled with micro-milling (LOMM) provides a feasible way to machine difficult-to-machine materials such as TiB2–TiC ceramic composites. The oxidation mechanism of the material under laser irradiation represents the fundamental issue of LOMM. In this paper, laser-induced controllable oxidation of spark plasma sintered TiB2–TiC ceramic composites as the workpiece material was studied. A three-dimensional finite element model was established based on ABAQUS/CAE 6.14 software to simulate the effect of laser parameters on temperature field distribution and was verified by experiments. The influence of laser processing parameters and assisted gas atmospheres on the oxidation behavior of TiB2–TiC ceramic composites was investigated. Results revealed that the irradiated temperature which had a significant impact on oxidation behavior, increased with an increment of the laser fluence and decreased with an increment of scanning speed with other laser parameters fixed. In addition, based on experimental analysis, the thickness of the oxide-layer increased with an increase of laser fluence and reduced with increasing laser scanning speed. At a laser fluence of 10.78J/cm2 and scanning speed of 1 mm/s as well as in an oxygen-rich atmosphere, a loose and porous oxide-layer was produced on the irradiated surface. Cross-section thicknesses of the oxide-layer and sub-layer reached 63 μm and 22 μm, respectively. Moreover, the thickness of the oxide-layer was 22 μm in air surroundings and hardly be found in argon and nitrogen atmospheres under identical laser parameters, which indicated that oxygen content had a significant influence on the oxidation reaction of the material. The products of the oxide-layer were mainly composed of rutile- and anatase-TiO2. Furthermore, the hardness of the sub-layer was 9.6 ± 0.7 GPa at a laser fluence of 10.78J/cm2 and scanning speed of 1 mm/s, which was far lower than that of the substrate with a hardness of 20 ± 0.7 GPa. This study provides a theoretical basis for subsequent micro-milling.

There are many approaches to address geospatial monitoring of pipeline overpasses, among which the most widespread methods are terrestrial laser scanning and total station measurements. However, there is a problem in comparing the geospatial monitoring data collected by different methods in different epochs. The main task of this work is to find the correspondence between points in different epochs. The total station measurements are carried out in specific discrete points of the pipeline overpass. In contrast, terrestrial laser scanning allows the collection of the whole data set without fixing specific point coordinates. In order to compare different data in different epochs, it is necessary to select a relevant presentation of the monitoring results (reference model) and specify appropriate criteria for quality inspection. In general, a pipeline can be presented as a spatial curve. In this study, two types of reference models are considered: cubic splines and Bezier curves. These models are examined for the monitoring of two gas pipeline overpasses. The first measurement epoch is accomplished by the terrestrial laser scanning, and the second measurement epoch is completed by the total station. The reference models are simulated by Matlab coding. The preliminary accuracy of ground laser scanning and total station measurement is selected as the criterion of quality inspection. The simulation and comparison results provide the evidence that the correct selection of reference model is a crucial component of successful geospatial monitoring. The results show that the Hermite splines are effective in the comparison of different data sets. These splines present the interpolation accuracy compatible with measurement accuracy, i.e., 15–20 mm for spatial displacement determination.

To improve the quality of narrow overlap welds and reduce cost during the high-strength production, it is essential to detect weld defects promptly by identification of the type of defects to provide solution accordingly. This paper proposes an integrated weld defect identification approach combing eddy current detection with 3D laser scanning based on Convolutional Neural Networks (CNN). The detection principle and equipment of the two detection methods are introduced. To fit the training process of CNN, two set of detection signals are preprocessed: a two-dimensional time-frequency diagram for eddy current signals using continuous wavelet transform and for laser images, weld edges are extracted and divided by region using image convolution and combining with integral graph. CNN model VGG16 is trained afterwards with data collected from one local manufacturer in Shanghai. It is discovered that performance of eddy current and laser image identification on different types of weld defects is different, and the accuracy can be increased with the two methods combined. Last, to achieve real-time detection of narrow overlap welding, a two-stage defect recognition model is built which greatly improves the efficiency of weld defect identification without affecting the accuracy of weld defect identification.

Correct measurement and qualification of failure mode for steel members are important for the development of member design methods, and have the potential to effectively identify the failure mechanisms of structures after disaster. Modern laser based geometric measurement technique can easily obtain 3D point clouds of member. However, rare studies have been reported on the deformation measurement from the geometric model reconstructed from 3D point clouds of an extensively deformed member. This study focuses on the automatic 3D geometric model reconstruction of steel column in failure state using the laser scanning technique and the qualification of the deformation. First, tests were carried out on steel I-columns subjected to axial compression to obtain two typical failure modes which were then transferred to 3D point clouds using the laser scanning technique. Afterwards, a rectangular coordinate system was built, and 3D point clouds were sliced into several cross-sections based on the plane-section assumption. The flanges and web were filtered out by applying thresholds to cross-correlation coefficient between the points’ normal and the unit vectors along the axes. A curve segmentation method using the image-based cross-correlation matching was proposed to accurately detect the corner points and weld regions in cross-section. The 3D geometric model was then reconstructed by assembling the cross-sections along the longitudinal axis of column. Finally, a cross-sectional constrained finite strip method (cFSM) was proposed based on the cross-sectional pure buckling modes generated using the classical cFSM method, which is more efficiency and robust. Both the proposed method and the classical cFSM method were used to qualify the deformation obtained from reconstructed 3D geometric model. Comparison of the qualification results between these two methods verified the validity of the proposed method.

The determination of a fully populated variance-covariance matrix (VCM) of a point cloud acquired with a terrestrial laser scanner (TLS) is not straightforward as physical correlations between TLS observations are not sufficiently known. Ignoring correlations leads to biased estimates, wrong modeling of surfaces, or the misinterpretation of geometric changes. For this reason, this study aims at progressing the empirical determination of correlations in TLS range observations by investigating short-scale correlations (mm to cm) of TLS rangefinders. Therefore, two methods are proposed to determine spatial correlations between TLS range observations. Both methods are evaluated for simulated laser scans, and then applied to empirical data of four different terrestrial laser scanners. The results demonstrate that short-scale correlations exist, and it is possible to quantify the relevant parameters to fill the VCM. It also shows that the correlation differs between the scanners and with the distance. Furthermore, we analyze the change of the correlation length with changing scanning configurations such as distance, incidence angle, and reflectivity with the result that this must be considered while applying the aforementioned methods to point clouds of large objects. All in all, this study trustfully quantifies physical short-scale correlations yielding from the rangefinder and suggests a guideline to apply this to point clouds of large objects.

This paper proposes a scanner–stage synchronized approach emphasizing a novel control structure for the laser polishing of Inconel 718 components manufactured by selective laser melting in order to address increasing demands for high surface quality in metal additive manufacturing. The proposed synchronized control system is composed of a motion decomposition module and an error synthesis module. The experimental results show that stitching errors can be avoided thanks to continuous motion during laser processing. Moreover, in comparison with the existing step-scan method, the processing efficiency of the proposed method is improved by 38.22% and the surface quality of the laser-polished area is significantly enhanced due to a more homogeneous distribution of the laser energy during the material phase change. The proposed synchronized system paves the way for high-speed, high-precision, and large-area laser material processing without stitching errors.

The method presented herein performs the tasks of identification, modeling, and registration refinement of poles using Light Detection And Ranging (LiDAR) point clouds. This method starts with a preliminary segmentation followed by eliminating outliers by integrating Fourier series and robust estimators. Poles’ cross sectional shapes are then identified by a customized template matching. Afterwards, points belonging to poles are extracted and the as-built model and registration-refined version of poles are generated. The algorithm was tested on five datasets including point clouds of three industrial sites, an urban environment, and a pole-like monument with very different volumes, resolutions, and configurations. The developed method works robustly despite the challenges that are often present in LiDAR data comprising outliers, non-uniform point sampling, gaps, and registration error. The obtained results indicate that 116 out of 117 poles in all five datasets were identified with no false positives at the object level. At point level, it reached greater than 98% average precision and 98% average accuracy in all datasets. Poles were modeled with a sub-millimeter precision in all datasets except for the third dataset in which poles were modeled with millimeter precision.

The precision machining of hard and ultra-hard materials by the laser beam is a key subject in the field of the modern manufacturing process. To improve the surface quality, the ablation threshold of a single pulse and the influence of the laser parameters on the surface characteristics of cemented tungsten carbide (WC-8Co) are firstly quantified and explored, where the material melting, the evaporation and the phase explosion are involved. The results also show that the scanning speed and the scanning times play important roles on the material removal efficiency. In addition, the crack formation seems to be inevitable under various parameters, where surface cracking in a certain direction to the laser scanning direction caused by the temperature gradient is found. The oxidization behavior is investigated by the XPS, the EDS and the Raman spectrum, which indicates that the main oxidation products are identified to be WO3, CoWO4, Co3O4 and CoO.

In this work, effect of sample size on mechanical properties in the net-shaped 316 L alloys produced by laser powder bed fusion (LPBF) was studied. Tensile specimens with four different geometries, having the same total cross-sectional areas but with different tension beam widths of 0.75, 1.5, 3 and 6 mm, were produced by the LPBF and subjected to the tests. The experimental results indicated that there is a strong influence of the sample size of the mechanical properties in the as-built state. The yield strength increased and the ductility decreased pronouncedly with decreasing the sample size. Fine grain structures near the surface of the net-shaped samples due to the additional laser contour scanning is believed to be responsible to the strong sample size effect. The experiments also revealed that the sample size effect can be effectively reduced with the annealing heat treatments. The local strength of the fine-grained area near the surface was quantitatively characterized by an inverse finite element analysis. The local strength near the surface was found stronger in the direction parallel to the LPBF building direction than in the direction parallel to the LPBF transverse direction, leading to more significant size effect along this direction.

The goal of this study was to investigate a study for the efficient generation of pillar-like nanostructure (nanopillar) on a material surface over a large area. In this research, a vertical cross-scanning (VCS) strategy using two linearly-polarized lasers with different laser conditions was proposed for the generation of nanopillars on a mirror-polished surface on a large scale. It found that the laser fluence and scanning speed of the second laser scanning should be controlled within a specific range to generate the nanopillars. Additionally, the distance between scan lines, which is defined as hatch distance, h, of the second scan, is also a non-negligible factor to induce nanopillars to cover the entire surface. This work demonstrated that the VCS method is a feasible strategy for the fabrication of nanopillars on the entire mirror-polished surface of Ti6Al4V alloy by linearly-polarized picosecond laser conveniently and efficiently.

The effect of the process gas during laser powder bed fusion (L-PBF) was investigated using high-speed shadowgraphy while melting Ti-6Al-4V powder under high purity argon, helium, and a mixture of both, on a laboratory-scale machine. These recordings reveal that the generation of incandescent spatters can be reduced by at least 60% using pure helium and by ∼30% using addition of helium to argon in comparison to the use of traditional argon. The quantity of colder spatters appeared unaffected by the change of process gas. Different configurations of gas flow versus laser scanning direction were investigated and revealed that fumes and spatters are less accumulated at the laser spot with helium addition. Furthermore, the use of the argon–helium mixture proved to be as efficient as pure argon in the dragging and extraction of the fumes. Shadowgraphs revealed the more rapid expansion of fumes in helium-rich atmospheres, limiting the accumulation of scattering objects close to the laser spot and thus melt pool instability. These results were correlated to process snapshots on an industrial-scale system, confirming the reduction of hot spatter generation. Finally, the findings put in evidence the more rapid cooling of spatters with helium addition to the process gas – a promising aspect to limit powder bed degradation during L-PBF. In addition, the use of mixtures of helium and argon would be economically interesting compared to pure helium, typically more expensive than the traditionally used argon.

In this paper, a novel approach was proposed to achieve the joining of AlN and Cu by nanosecond laser pre-irradiation of AlN. The effects of the speed of laser scanning on the morphology, chemical compositions, and properties of the surface of AlN ceramic and the mechanism of laser-assisted joining of AlN and Cu were investigated. With the increase of the speed of laser scanning, the surface roughness of AlN decreased. After nanosecond laser irradiation, element Al was detected on the surface of AlN. When nanosecond laser irradiation was applied, the hydrophilicity and the surface energy of the ceramic surface were improved. The modified AlN was successfully joined to Cu at the temperature of 620 °C with a speed of laser scanning of 500 or 1000 mm/s. The results of TEM confirmed the presence of Al4Cu9, indicating the metallurgical combination of Cu and AlN. Also, the method presented in this paper was supposed to be of great reference significance for the joining of ceramics and metals.

The analysis of topographic time series is often based on bitemporal change detection and quantification. For 3D point clouds, acquired using laser scanning or photogrammetry, random and systematic noise has to be separated from the signal of surface change by determining the minimum detectable change. To analyse geomorphic change in point cloud data, the multiscale model-to-model cloud comparison (M3C2) approach is commonly applied, which provides a statistical significance test. This test assumes planar surfaces and a uniform registration error. For natural surfaces, the planarity assumption does not necessarily apply, in which cases the value of minimal detectable change (Level of Detection) is overestimated. To overcome these limitations, we quantify an uncertainty information for each 3D point by propagating the uncertainty of the measurements themselves and of the alignment uncertainty to the 3D points. This allows the calculation of 3D covariance information for the point cloud, which we use in an extended statistical test for equality of multivariate means. Our method, called M3C2-EP, gives a less biased estimate of the Level of Detection, allowing a more appropriate significance threshold in typical cases. We verify our method in two simulated scenarios, and apply it to a time series of terrestrial laser scans of a rock glacier at two different timespans of three weeks and one year. Over the three-week period, we detect significant change at 12.5% fewer 3D locations, while quantifying additional 25.2% of change volume, when compared to the reference method of M3C2. Compared with manual assessment, M3C2-EP achieves a specificity of 0.97, where M3C2 reaches 0.86 for the one-year timespan, while sensitivity drops from 0.72 for M3C2 to 0.60 for M3C2-EP. Lower Levels of Detection enable the analysis of high-frequency monitoring data, where usually less change has occurred between successive scans, and where change is small compared to local roughness. Our method further allows the combination of data from multiple scan positions or data sources with different levels of uncertainty. The combination using error propagation ensures that every dataset is used to its full potential.

A single-step reduction and patterning technique that involves high-pulse nanosecond fiber laser irradiation was used to reduce graphene oxide films (GOFs) for use in ceramic-based heaters. Laser reduction of GOFs was performed at a laser power, scan speed, pulse repetition frequency, and laser scan pitch of 2.2–4.1 W, 150–500 mm/s, 750 kHz, and 10 μm, respectively. The optimal intensity ratios of the D to G band (RD/G) and the 2D to G band (R2D/G) of reduced GOFs (RGOFs), obtained from Raman spectra, were 0.251 and 0.587, respectively. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that oxygen-containing functional groups in RGOFs coated onto ceramic substrates were removed by increasing the average laser power and decreasing the laser scanning speed. Moreover, the typical RGOFs exhibited a lowest sheet resistance of 22.75 ± 2.75 Ω/□, which was achieved with an average laser power and scan speed of 3.35 W and 300 mm/s, respectively. The highest temperature of the typical laser-patterned RGOFs was approximately 123.3 °C, which occurred when the RGOFs were produced using a laser power, scan speed, and applied direct current voltage of 3.27 W, 200 mm/s, and 10 V, respectively.

Surfaces processed by scanning with a pulsed laser have an inherent roughness due to the partial overlap of discreet pulses. Experimentally optimising the parameters to minimize roughness is challenging because of the time and effort required. A computational model based on the finite volume method for predicting surface roughness during laser surface processing is presented in this work. The data obtained from a single pulse model is used to predict the surface profile by overlapping the successive pulses based on scanning speed. The model captures numerous physical phenomena such as laser absorption, heating, melting, vaporisation, plasma effects, melt pool flow and solidification, as well as the effect of laser scanning. The surface roughness values (Ra and Rq) obtained using the model are reasonably within the limits of the experimental data. The results reveal that the effect of laser parameters on surface roughness is non-linear. While the ablation depth increases exponentially with a decrease in scan speed, the local maximum and minimum of surface roughness could be in the parameter range's intermediate values. The model developed in this work can be used to optimise the processing time and surface finish in different laser-based surface processing techniques.

Previous research work shows that metal nanocomposite thin films fabricated by laser sintering of mixtures of metal nanoparticles (NPs) and carbon nanotubes (CNTs) on a polymer substrate have a great potential to help enhance reliability and durability of metal components in flexible electronic devices. To gain a good relevant fundamental understanding, it is important to know the material thermal history during laser sintering. However, an in-situ temperature measurement has been rarely reported in a paper in the literature for laser sintering of metal NP-CNT mixture thin films on a polymer substrate. Such temperature measurements are reported in this paper, which are performed using a two-color pyrometry system set up by the authors to overcome related technical challenges such as high spatial and temporal resolution requirements. The measurement method is non-contact, and by measuring thermal radiation in two wavelength ranges it does not require the value of the target surface emissivity. The electrical resistivities of composite material sintered with different laser scanning speeds are also measured. Under the conditions studied, it has been found that as the laser scanning speed increases significantly, the average melted material temperature in the measurement spot only slightly decreases, but the melting duration drops significantly. The average electrical resistivity of sintered composite material first decreases and then increases with the laser scanning speed. The measured material surface temperatures for laser sintering of CNT and silver NP mixtures are similar to those for laser sintering of silver NPs with the same laser scanning speed.

Ag mesh transparent conductive films (TCFs) were prepared on the commercial FTO/Glass substrate by ultrafast laser direct writing, trying to improve its overall photoelectric performances. The effects of laser scanning speed, laser fluence and Ag mesh height on photoelectric properties of the Ag mesh/FTO TCFs were systematically studied. The results indicated that a small scanning speed or a high laser fluence would cause excessive ablation of the FTO film and result in an increased Ag mesh line width, which was detrimental to the photoelectric properties of the resulting TCF. It was found that the optimal parameters for fabricating Ag mesh/FTO TCFs were a laser scanning speed of 2200 mm/s, a laser fluence of 0.050 J/cm2 and an Ag mesh height of 2500 nm. The as-fabricated TCF possessed the highest figure of merit of 13.03 × 10−2 Ω−1, which was significantly superior to that of the commercial FTO film. Finally, transparent heaters (THs) were prepared respectively based on the optimal Ag mesh/FTO TCF and the FTO/Glass substrate. The Ag mesh/FTO TH exhibited a more excellent heating performance than the FTO TH, further confirming that the overall photoelectric performance of the FTO/Glass substrate had been greatly improved.

Laser-based surface modification methods are employed to augment the surface properties of engineering components. In the presented work, pulsed laser remelting of Ti6Al4V surfaces using a long pulsed laser was used to generate ripple-like micro-features with different feature sizes. The resultant surfaces exhibited improved corrosion and tribocorrosion resistance. Anisotropic wetting characteristics of the laser remelted surfaces led to elongation of water droplets on the surfaces. The osteogenic potential of the surfaces as well as the orientations of human mesenchymal stem cells on the surfaces were dependent on the surface features. On surfaces having 20 μm ripples, differentiation of stem cells towards osteoblastic lineage was higher than that on acid etched surfaces, and the cells were prominently oriented across the ripples, parallel to the laser scanning track. On the other hand, surfaces having 100 μm ripples suppressed the cellular activities on them. While the resistance to corrosion and tribocorrosion of laser remelted surfaces can be attributed to the evolved microstructure and the formation of stable oxide layers, the physical characteristics like topography and wettability dictated cellular behavior on the surfaces. Taken together, the work demonstrates the use of pulsed laser remelting as a simple yet potentially effective route towards manufacturing Ti6Al4V orthopedic implants with improved biofunctionalities.

This paper reports an experimental investigation on continuous CO2 laser cutting of polymethylmethacrylate (PMMA) sheet. The influence of four process factors (laser power, cutting speed, assisting gas pressure and sheet thickness) on five process responses (kerf deviation, top heat affected zone, bottom heat affected zone, maximum surface roughness and rough area) has been investigated. The experimental plan was established based on Taguchi L18 mixed design. The kerf geometry and heat affected zones have been measured using polarising light microscopy technique, while the surface roughness was evaluated using 3D laser scanning confocal microscope. Regression models have been derived to correlate different process responses with different process factors. The cut surface could be classified into three zones: rough zone, moderate zone and soft zone. The rough area is increased by increasing gas pressure and laser power and by decreasing the sheet thickness and cutting speed. Increased kerf deviation has been observed at high cutting speed, laser power and gas pressure. High laser power and low cutting speed produced worst surface roughness and wide heat affected zone. Therefore, it is recommended to use low laser power and high cutting speed to minimize the heat affected zone and the surface roughness. However, increasing the cutting speed may result in high kerf deviation.

The measurement of surface moisture on beaches is vital for studying aeolian sand transport mechanisms, but existing techniques are not adequate for monitoring the surface moisture dynamics over a substantial beach section. In this study, we investigated the suitability of a new remote sensing method to monitor the spatiotemporal variation in surface moisture on a sandy beach using a long-range static terrestrial laser scanner (TLS). The TLS was permanently deployed on top of a 42 m high building overlooking the study site at Ostend-Mariakerke, Belgium. Considering the effect of target surface roughness on the intensity and the laboratory’s length limitation, a new intensity correction method is proposed which only uses the field point cloud data measured on a homogenous beach surface (without time-consuming indoor experiments). Based on the corrected intensity data, the relation of the beach surface moisture to the corrected intensity was modeled by an exponential model with a correlation-coefficient squared of 0.92. A moisture estimation model was developed which can directly derive the beach surface moisture from the original intensity data of the TLS with a standard error of 2.27%. The hourly surface moisture dynamics across two tidal cycles on the beach were investigated as a case study, in which the point clouds derived from corresponding unmanned aerial vehicle (UAV) imagery are utilized to improve the calculation accuracy of the incidence angles of TLS point clouds at long distances. Results reveal that, after the intensity correction, the long-range static TLS is an extremely suitable technique to monitor the surface moisture dynamics (daytime and nighttime) over a substantial beach section (hundreds of meters) at a high scanning frequency (minutes to hours).

Alongside spatial information, an intensity scalar is also measured by LiDAR (Light Detection And Ranging) sensor systems. It corresponds to the amplitude of the backscattered laser beam after reflection on the scanned surface. This information isn’t directly usable due to dependencies of geometrical parameters occurring during the scanning process and additional processing modifications. The research community, in a growing trend, invests efforts to convert this signal into a value which could bring qualitative and quantitative new applications. We propose in this paper, a review of the theortical background of LiDAR radiometric calibration, from physical background to state-of-art methodology. A comparison of two approaches to eliminate geometrical (range and incidence angle) and instrumental dependencies of intensity measurement is presented. Their application on several homogeneous areas of a real-world case study shows a significant reduction of intensity variation between surfaces with identical material composition. Finally, a linearization process permits to obtain an equivalent Lambertian reflectance value which, by its disciminant potential, could be specifically suitable for some algorithms like segmentation or registration.

The laser ablation treatment has been validated to be an effective surface treatment method in improving adhesive bonding performance for metal or composite materials. This study was further conducted to investigate the effect of laser spot overlap ratio on surface characteristics and resultant adhesive bonding strength for AA6022-T4 Al alloy. The laser spot overlap ratio was changed by varying the laser processing speed and line spacing between laser scanning lines. Surface characteristics analyses show that the laser ablation treatment at higher overlap ratio produces rougher surface morphology and thicker aluminum oxide layer on substrate surface, which are considered to be more favorable for adhesive bonding strength. Lap-shear strength results show that the laser ablation treatment at overlap ratio of -49 % (corresponding with separated laser spots) improves the joint strength by 6.8 % and 17.1 % before and after water soak exposure compared to as-received condition. Meanwhile, the desired cohesive fracture mode is also achieved which indicates that the joint strength reaches to the saturated value depending on mechanical performance of adhesive. This explains that the continuous increase of laser spot overlap ratio from -49 % to 63 % exhibits negligible improvement on joint strength. Nevertheless, although inducing a higher degree of surface physicochemical modifications on Al substrates, the laser ablation treatment with an overlap ratio beyond 63 % decreases the joint strength. Detailed studies of SEM micrographs verified that the decreased joint strength is attributed to insufficient wetting of adhesive on the rough surfaces of laser-treated substrates resulting in entrapment of air between substrate and adhesive layer, which forms micropores defects in the adhesive layer and consequently weakens the adhesive-bonding joints. In addition, the improved corrosion resistance of adhesive-bonded Al joints by laser ablation treatment is attributed to the barrier effect of laser-produced rough surface morphology to water diffusion along bonding interface.

In order to achieve high-efficiency machining of Fresnel microstructure, an improved laser scanning contour ablation (LSCA) method with continuously variable feedrate was proposed based on the theoretical model of the material removal depth. The silicon carbide (SiC) Fresnel microstructure was machined by the improved LSCA method and characterized by multiple means. The experimental results showed that the crystallinity of SiC decreased and amorphous Si and SiO2 were generated on the SiC Fresnel microstructure. The form profile error PV was less than 5 μm, the average verticality error of the step sidewall was 34.6°, the surface roughness was Sa 0.237 μm–0.343 μm, the subsurface cracks depth was 1–1.5 μm. The material removal rate (MRR) of machining SiC Fresnel microstructure by using the improved LSCA method could achieve 0.2875 mm3/min, which was much higher than the MRR of mechanical machining and reflected the efficiency advantage of laser to process hard and brittle materials.

Microneedle arrays are minimally invasive devices which enable self-administration of drugs in a straightforward and efficient way. Recently, a low-cost mass production method to produce solid polymer microneedles using laser ablated moulds in an injection moulding process has been developed. In this context, it is key to understand how the geometry of the microneedle cavities can be changed and what parameters affect the replication fidelity during injection moulding. In this study, two laser scanning parameters, being the programmed base diameter and the number of layers were varied in four levels and their effects on the geometry of the microneedle cavities were evaluated in tool steel, copper alloy, and aluminium alloy inserts. Afterwards, the microneedle cavities were replicated in polypropylene and polycarbonate using injection moulding. The study showed how the depth and base diameter of the microneedle cavity can be changed by varying laser scanning parameters. Moreover, the moulds in the three materials exhibited different microneedle cavity shapes and dimensions, due to differences in material properties. As to the injection moulding process, strong linear relationships were found between the aspect ratio of the microneedle cavities and the replicated thermoplastic microneedles, where a higher aspect ratio resulted in a lower replication. The replication fidelity for the polypropylene microneedles was in all cases higher compared to the polycarbonate needles. Between the three mould materials, a comparable replication fidelity was found for tool steel and copper alloy and a lower replication for the aluminium alloy, due to differences in thermal and wetting properties.

The surface morphology of parts made by the laser powder bed fusion (L-PBF) process is governed by the flow of the melt pool. The nature of the molten metal flow depends on the material properties, process parameters, and powder-bed particles, etc., and may result in potentially significant variations along a laser scanning path. This study investigates the formation of transient and steady-state zones through a single-track l -PBF experiment using Inconel 625 powder. Single tracks with lengths of 1 mm and 2 mm were fabricated using 195 W laser power and scan speeds of 400 mm/s or 800 mm/s. The surface morphology of the track was analyzed using a white light interferometer (WLI), and an individual single track can be divided into three distinct zones based on the track width and height. The initial transient region has a wider and taller solidified track geometry, the region near the end of a scan has a tapered profile with a decreasing track width and height, while the steady-state region in the middle has a smaller variation in the width and height. A mesoscale numerical model was further developed using FLOW-3D to examine the formation of the transient and steady-state zones. At the start of a scan, strong flow occurs outward and backward, leading to the formation of a wider track with a bump. As the scan continues, the thermal gradient stabilizes, leading to a steady state, which resulted in a very small fluctuation in the width. Furthermore, the tapered end of the scan track is due to the half-lemniscate shape of the melt pool during laser scanning.

The paper describes the method of using laser scanning as a way to help identify problems and collisions that cannot be detected using 2D drawings. The study shows the advantages of creating an information model of a metro station using point clouds, compared to creating a model based only on ready-made drawings. The main goals of creating digital twins of underground complexes – metro stations-are listed in the paper and an algorithm for transferring a real object into a 3D model is considered. As an example for the study, an underground object was considered – a metro station that requires reconstruction and was built in the 1950s. As a result of processing the initial laser scanning data, a number of issues were found that need to be resolved: the object does not meet the standards for dimensions, it is not possible to place / bring equipment, and the station subsidence. It is concluded that the use of laser scanning to create a 3D model of underground complexes-metro stations helps to detect errors and potential problems at the design stage. Such problems cannot be identified using 2D drawings, so the availability of laser scanning results gives an advantage during construction and reconstruction.

In this work, two methods for predictive shimming based on laser scan technology and point cloud processing software have been presented. The first one is direct measurement method in PolyWorks, and the second one is feature-based modelling method in SolidWorks. Firstly, both component-level and assembly-level scans are collected by a laser scanner. Then, the point clouds are post-processed and registered in PolyWorks. Thirdly, gap information (shape and thickness) is obtained either in PolyWorks or in SolidWorks. Results show that the proposed methods can obtain gap information successfully based on current hardware and software.

Additive manufacturing in recent years has become a popular and well-known method. The method, which involves 3D printing, provides possibilities for the creation of innovative prototypes and technologies for manufacturing. Our paper describes an idea of combining 3D printing with nanoclay. The addition of nanoclay will enhance the share of renewable raw materials that contribute to sustainable products. The structure of the filaments varies, however, as nanoclay is applied. The key goal of the paper is to establish methodologies for improving the properties of 3D composite filaments nanoclay and polyethylene. A comprehensive literature research including the extrusion, 3D printing and modern testing methods, including the 3D scanning, was paired with a large experimental analysis to evaluate printed versions. 3D printing filaments were produced for different ratios of polypropylene and nanoclay in the extruder. Significant parameters were reported for the extrusion of related content. After the introduction of nanoclay, the dimensional flexibility of polypropylene was enhanced and the deformation of the 3D printed models decreased significantly. However, fragility in filaments and 3D models increased, with the increased nanoclay ratio.

Rapid heating, melting, solidification and cooling cycles generates high residual stress in additively manufactured parts, causes to part distortion. Finite Element Method (FEM) is one of the common and practical ways to predict residual stress and distortion taking place during additive manufacturing. Thus, it is possible to determine appropriate parameters to eliminate such problems. In this study, laser powder bed fusion (LPBF) additive manufacturing (AM) of Inconel 718 alloy is considered for simulation. Case studies on the residual stress and distortion of arch-shaped structure parts were presented through comparing the simulation results in present study and experimental data borrowed from the literature. The influence of laser scanning parameters such as laser power, scanning speed, layer thickness, scanning strategy on residual stress and distortion of the arch-shaped structure was investigated and compared with the borrowed experimental results. Besides, the influence of heat treatment on residual stress and distortion is also simulated and predicted results are presented. This study reveals that the presented FEM based simulation is capable of capturing experimental data reasonably well.

Laser cladding is a very popular technique for the process of providing protection to the surface of materials that are subjected to extreme working conditions. This article describes the process where Stellite 6 alloy is added on to the surface of EN8 steel in a controlled manner. EN8 steel is the material that is used as a base material as it the commonly used material in the manufacturing sector. Stellite 6 is a cobalt base super alloy which is characterized by extreme wear resistance and high hardness. The laser cladding process is done whilst considering parameters like laser scanning speed, laser focus height, laser power and powder feed. The laser cladded samples are corrosion tested in an acidic environment and the electron images of the samples are taken. From the electron microscopy images the corrosion is classified in order to be fed to a fuzzy logic model. This fuzzy logic model is used to deduce a corrosion index and this corrosion index is further optimized using Taguchi method and the results have been reported.

Turbine blade cores are made of porous alumina ceramic and determine the molding accuracy of the cavity of turbine blades, which strongly affect thermal diffusion performance and service life of turbine engines. To get a high quality ceramic core, accurate trimming for a preliminarily processed core is needed and therefore, micromachining porous alumina ceramic, which differs from general alumina substrates, is crucial. This paper dealt with a processing technology for the special material via double femtosecond laser scanning. The materials ablation threshold was firstly determined through parameter fitting and then this material was machined at a combination of different laser processing parameters. Considering the produced debris blocks the lasers further propagation into the material, double femtosecond laser scanning was newly proposed and experimentally verified with the comparison of gas jet assist and underwater laser processing ways. The removal profiles of the machined material were characterized in terms of cutting width, cutting depth, deviation of linearity and surface morphology, which exhibited high dependence on the femtosecond laser processing parameters. The optimal laser operating window was identified and high quality laser cutting of the porous alumina ceramic was demonstrated. The developed processing technology has potential application in trimming for ceramic casting cores. In addition, it might also give a novel view for high quality laser micromachining another materials.

Selective laser melting (SLM) is an additive manufacturing process, which allows for producing parts of very complex geometry. While SLM may produce the desired net-shape geometry, the surface conditions of as-built SLM parts are often insufficient. Also, the as-built state may yield undesired tensile stresses at the surface. Post processes such as magnetic field-assisted finishing (MAF) processes can yield the desired surface roughness and improve the residual stress state. However, in a part made by SLM, these processes will act on surfaces with various different orientations to the built direction, and, in particular, to the laser scanning direction. This paper analyzes the influence of laser scanning direction with respect to the surface to be finished by MAF using 316L steel disks produced with different orientations and scan strategies. The build plane of an as-printed disk has greater surface roughness and hardness but lower tensile residual stresses than the plane perpendicular to the build plane. These characteristics create difficulties in material removal and smoothing but do not impede MAF’s ability to increase hardness and impart compressive residual stresses to the surface scanned by the laser. The results indicate that material removal rate and hence optimal finishing time depend on the orientation of the surface with respect to the scanning direction, which should be accounted for in process planning.

Titanium carbide MXene (Ti3C2Tx, where Tx refers to -Cl, –F, –OH and ​= ​O) shows ultrahigh electronic conductivity but restricted rate performance for supercapacitors due to prolonged ion transport caused by the restacking of 2D materials. In this work, an ultrafast laser writing technique is used for alleviating the restacking issue by opening up the restacked layers and creating pores through instantaneous photothermal gasification of interlayer water and partial surface groups. The rate performance of Ti3C2Tx film is effectively improved after laser writing. By tuning the line density of laser scanning path, the electrochemical performance can be well controlled and an optimized high capacitance of 322 ​F ​g−1 at 10 ​mV ​s−1 is obtained at relative high rate performance, showing a high capacitance retention of 48% as the scan rate increased by 200-fold. As a result, the symmetric microsupercapacitor with laser written Ti3C2Tx electrodes exhibits a high areal capacitance of 15.03 ​mF ​cm−2 at 10 ​mV ​s−1 with ultrahigh capacitance retention of 33% at 2000 ​mV ​s−1. Moreover, the laser writing process takes only ~1 ​s for an 1 ​cm ​× ​1 ​cm square film, showing superior advantages over other methods and potentials in scale-up production.

We present an approach for automatically detecting the positions of tree trunks, for determining their corresponding diameter at breast height (DBH), and for assessing the shape of tree trunks from 3D point clouds derived from unmanned aerial vehicle borne laser scanning (ULS). The experiments are carried out with point clouds from both a RIEGL miniVUX-1DL and from a RIEGL VUX-1UAV. The results reveal that the autonomous stem detection recognizes 91.0% and 77.6% of the stems, respectively, and that the DBH can be modeled with biases of 2.86 cm and 0.95 cm for 80.6% and 61.2% of the trees, when compared to field measurements. We further demonstrate that, compared to terrestrial laser scanning (TLS) data, the stem diameters along the tree can be estimated with biases below 3.4 cm and 1.4 cm for the two systems, respectively, up to a tree height of 12 m for stems with a DBH above 20 cm. Our experiments further reveal the accuracy of diameter estimations to be mainly dominated by the tree’s diameter with better accuracies for larger stems, while the completeness, with which a stem is covered by points, has little influence, as long as half of the stem circumference is captured. The absolute point count on the stem does not impact the estimation accuracy of all stem parameters, but is critical to the completeness with which a scene can be reconstructed. Conversely, we demonstrate the precision of the laser scanner to be a key factor for the accuracy of the stem diameter estimations, as in our experiments, we found the accuracies of the estimations from the VUX-1UAV to be higher than the ones from the miniVUX-1DL. The findings of our study assist to evaluate the potential of ULS for forest monitoring and management and allow for conclusions regarding the required point cloud qualities and, thus, the mission planning of ULS acquisitions, in order to deliver data products, which fulfill the requirements for an operational application in forest inventories.

Laser scanning has played an important role in many fields of industrial production, such as product defect detection, reverse engineering and so on. Automatic laser scanning is the key technology to improve scanning efficiency and accuracy. This paper presents a method for planning laser scanning trajectory, especially for the objects with unknown model. This method is also suitable for painting and welding operations. Mask R-CNN is used to segment RGB images. Combined with the well-registered depth map, rough point cloud of processed objects can be extracted, which can be used as the basis of trajectory planning. In the part of trajectory planning, after extracting the outline of objects from rough point cloud information, the least square method is used to smooth the trajectory. In the actual scanning process, a method of real-time adjusting sensor position and posture by using PID controller is proposed to optimize the collected data. Finally, we construct an actual scanning system to verify the effectiveness of our method.

The material removal and the surface formation mechanism of C-plane sapphire in multipass ablation using a nanosecond laser were investigated. The surface morphology and the width and depth of the grooves under different laser-processing parameters were characterised and investigated based on an analysis of the laser energy fluence distribution in time and space, which determines the obtained depth and width of the groove. The results show that the material removal mechanism in the sapphire processed using a nanosecond UV laser was a mixture of thermal and photochemical effects. The laser thermal effect caused sublimation, vaporisation, melt, and sputtering by plasma and was characterised by the resolidified bulk area and the deposition of fine particles. Surface cracking in a certain direction to the laser scanning path was also observed because of the gradient-temperature-induced thermal stress. In addition, the photochemical effect was revealed by the obtained X-ray photon spectra, in which the appearance of a metal Al peak and a decreasing O1s peak after laser ablation indicated the photolysis of Al2O3.

Silicon carbide has a high hardness and corrosion resistance. Accordingly, high rate machining of this material is a big challenge to obtain good surface quality. In this work, plasma etching aided femtosecond laser micromachining was proposed to address this issue. A series of square and circular blind holes for forming SiC pressure sensor diaphragms were obtained by using a 50fs, 800 nm, 1000Hz Ti:Sapphire laser. Using the control variable method, the effects of laser machining power, scan line spacing and scanning rate on surface topography of the structure were investigated. As demonstrated by experimental results, surface roughness of the structure increases with the laser machining power within a certain range. While the scanning rate has negligible effects on surface quality of the structure. The maximum surface roughness after femtosecond laser micromachining is 2.867 μm measured by laser scanning confocal microscope, and this value is reduced to 2.143 μm after inductively coupled plasma etching. In addition, a Raman spectroscopy shows that this composite micromachining method can eliminate accumulation of amorphous carbon on SiC surface caused by the femtosecond laser processing. The reduction of surface roughness and removal of amorphous carbon can effectively decrease probability of crack failure of the sensor diaphragm and increase its deformation capability, thereby ensuring sensitivity of the sensor. The composite micromachining method fully combines the advantages of high efficiency of femtosecond laser machining and high surface quality of plasma etching, making it has high potential to be applied in precision machining of silicon carbide and fabrication of SiC sensors.

The laser scanning method is one of the key factors in the process of selective laser sintering. Laser sintering and invalidating composite (LSIC) scanning method, which is composed of high tensile strength sintering scanning with large-spot and high accuracy invalidating scanning with small-spot, is able to improve the tensile strength, accuracy and fabrication efficiency of SLS parts. In this paper, the principle and implementation of this method were presented, and in order to prove the effectiveness of the method, the conventional scanning method was used to carry out the sintering forming experiments of the coated ceramics, and the relationship between the energy density, the tensile strength and accuracy of the parts was explored. Then based on the conclusion of this experiment, the composite scanning method is used for comparative sintering experiments. The results show that when the sintering process is carried out using the process parameters corresponding to the high tensile strength, a substantial amount of secondary sintered bodies is generated on the surface of the part and the accuracy is destroyed. The conventional scanning method cannot achieve high accuracy forming under this process condition. However, the composite scanning method can effectively eliminate the adverse influence of secondary sintering on accuracy, and achieve high tensile strength and high accuracy parts. Moreover, the method can also improve the fabrication efficiency. Therefore, this method is of great significance to realize high quality sand mould additive manufacturing and enrich the scanning method of SLS.

Laser treatment of SiAlON surface is considered and characteristics of the resulting surfaces are studied incorporating the scanning electron and atomic force miscroscopes, X-ray diffraction and Fourier transform infrared spectroscopy. The wetting state of the laser treated surface is assessed using the droplet contact angle method while the friction coefficient of the treated surface is obtained by using the micro-tribometer. Microhardness and fracture toughness of the treated surface are also measured. Thermal and thermal stress analyses are carried out and temperature and von Mises stress fields are predicted in the laser treated region. It is found that in micro/nano size pillars are formed on the laser treated surfaces, which alters the wetting state from hydrophilic to hydrophobic with contact angle 120° and contact angle hysteresis in the order of 18.2°. In general, laser treated surface is free from large size cracks and voids; however, few locally scattered micro-cracks are observed on the surface. Microhardness increases slightly for the laser treated surface because of the dense layer formed on the surface under the high cooling rates. The fracture toughness of the surface reduces slightly and the friction coefficient of the surface improves after the laser treatment process. The laser scanning tracks, which are closely spaced, result in self-annealing effects in the laser treated region; in which case, von Mises attains low values particularly along the recently formed laser scanning tracks.

The use of three-dimensional (3D) optical instruments to measure soft tissue facial characteristics is increasing, but systematic assessments of their reliability, practical use in research and clinics, outcome measurements, and advantages and limitations are not fully established. Therefore, a review of the current literature was performed on the reliability of facial anthropometric measurements obtained by 3D optical facial reproductions as compared to conventional anthropometry or other optical devices. The systematic literature search was conducted in electronic databases following the PRISMA guidelines (PROSPERO registration: CRD42018085473). Overall, 815 studies were identified, with 27 final papers included. Two meta-analyses were conducted. Tested devices included conventional cameras, laser scanning, stereophotogrammetry, and structured light. Studies measured living people or inanimate objects. Overall, the optical devices were considered reliable for the measurement of linear distances. Some caution is needed for surface assessments. All instruments are suitable for the analysis of inanimate objects, but fast scan devices should be preferred for living subjects to avoid motion artefacts in the orbital and nasolabial areas. Prior facial landmarking is suggested to improve measurement accuracy. Practical needs and economic means should direct the choice of the most appropriate instrument. Considering the increasing interest in surface-to-surface measurements, fast scan devices should be preferred, and dedicated protocols devised.

By utilizing the airborne laser scanning (ALS) and terrestrial laser scanning (TLS), the land surface information from both top view and side view can be captured rapidly. However, due to the different perspective views, resolutions, and ranges, the automatic localization of multiple TLS scans to ALS is challenging. To address this issue, this paper proposes a novel skyline context-based method. First, the ground points in ALS are extracted and used as potential TLS locations, and the corresponding skyline contexts are generated. After that, a 3D skyline-based k-d tree is built for searching the corresponding coarse localizations of TLS scans. The final refinement is done by the trimmed iterative closest point algorithm (T-ICP). 5 datasets with different ALS sizes and over one hundred TLS scans are undertaken to evaluate the performance of the proposed method. For one ALS data with mean point distance of 0.1 m, the average localization accuracy reached about 0.13 m. The experimental results indicate that the proposed method performs well for automatic localization of TLS scans to ALS point clouds, with advantages in both precision and adaptability.

New technologies, such as unmanned aerial vehicles (UAVs) and terrestrial laser scanning systems, provide opportunities for the digital documentation of cultural heritage. Although ultra-light drones (ULDs) are usually used for recreational activities, in this study, we examined their ability for use in digital documentation. We investigated the efficiency of an ULD for documentation of a selected historical building. In this study, the structure from motion (SfM) method was used to create three-dimensional point cloud data of a historical building using ULD and a low-cost UAV. The resulting point clouds were compared with terrestrial laser scanner data. The maximum standard deviations were calculated as 0.62 cm and 1.87 cm for low-cost UAV and ULD, respectively. The results show that ULDs can be used under suitable circumstances as a low-cost alternative for cultural heritage documentation. (C) 2020 Elsevier Masson SAS. All rights reserved.

Segmenting accurately point clouds is of great relevance in several fields of engineering and construction. Users are interested in properly dividing an point cloud into their components and then recognizing them. Point clouds representing historical buildings present an additional challenge because image details could be related to a cultural or architectural aspect. Therefore, the way the results are evaluated is also important. In this paper, we present a novel point cloud approach for segmenting historical building of different architectural styles and periods. In our approach, that works for organized and unorganized point clouds, we combine Hierarchical Watershed Transform and curvature analysis from region growing methods in order to obtain more suitable seeds. Experiments were conducted involving historical building acquired using drones and terrestrial laser scanner. The data was combined into a single point cloud. Finally, we evaluated our results qualitatively and quantitatively, by comparing them to a dataset containing the ground truth. The quantitative metrics demonstrate the effectiveness of our method when compared with state-of-the-art methods.