TLS Measurements Research Articles

Management of complex pilon fractures: Is it necessary to fix all the columns in AO/OTA type 43-C fractures?

IntroductionSurgical treatment of AO/OTA 43-C pilon fractures has not yet taken a standard form. We aimed to evaluate whether patients that appeared to be labelled as unsupported columns according to the four-column theory would affect long-term clinical and radiological outcomes. Materials and MethodsPatients with AO/OTA 43-C type who were treated surgically between January 2010 and December 2019 were included in the study. 53 fractures in 52 patients who received osteosynthesis were categorized based on the fixed columns. These groups were formed as fully supported columns (FSC- Group A), partly supported columns (PSC-Group B), Ankle range of motions (ROM), Burwell Charnley's reduction evaluation criteria, Kellgren-Lawrence ankle osteoarthritis staging system, and American Orthopedic Foot and Ankle Society (AOFAS) Scoring System, Olerud-Molander Ankle Score, Visual Analog Scale were used for evaluating radiological and functional outcomes. ResultsThe mean follow-up period was 72.6 (12–131) months. Mean age was 42.6 (18–76). Two groups were homogenously distributed in terms of age (p = 0.785), sex (p = 0.376), laterality (p = 0.732), smoking status (p = 0.488) and reduction quality. There was no difference in AOFAS score (p = 0.452), Olerud-Molander score (p = 0.354) and VAS scores (p = 0.589). TAS, TLS and TT angle measurements suggested no difference between groups (p = 0.493, p = 0.834, p = 0.577). There was no difference between groups in terms of infection (p = 0.734), malunion (p = 0.688) and arthritis (p = 0.483) ConclusionWe presented findings that contradicted the hypothesis positing the existence of four distinct columns in pilon fractures, as well as the notion that each fractured column requires support from distinct implants. Level of EvidenceLevel III

Suitable LiDAR Platform for Measuring the 3D Structure of Mangrove Forests

Investigating the three-dimensional structure of mangrove forests is critical for their conservation and restoration. However, mangrove forests are difficult to survey in the field, and their 3D structure is poorly understood. Light detection and ranging (LiDAR) is considered an accurate and dependable method of measuring the 3D structure of mangrove forests. This study aimed to find a suitable LiDAR platform for obtaining attributes such as breast height diameter and canopy area, as well as for measuring a digital terrain model (DTM), the base data for hydrological analysis. A mangrove forest near the mouth of the Oura River in Aza-Oura, Nago City, Okinawa Prefecture, Japan, was studied. We used data from terrestrial LiDAR scanning “TLS” and unmanned aerial vehicle (UAV) LiDAR scanning “ULS” as well as data merged from TLS and ULS “Merge”. By interpolating point clouds of the ground surface, DTMs of 5 cm × 5 cm were created. DTMs obtained from ULS could not reproduce the heaps of Thalassina anomala or forest floor microtopography compared with those obtained from TLS. Considering that ULS had a few point clouds in the forest, automatic trunk identification could not be used to segment trees. TLS could segment trees by automatically identifying trunks, but the number of trees identified roughly doubled that of the visual identification results. The number of tree crowns identified using TLS and ULS was approximately one quarter of those identified visually, and many of them were larger in area than the visually traced crowns. The accuracy of tree segmentation using the canopy height model (CHM) was low. The number of canopy trees identified using Merge produced the best results, accounting for 61% of the visual identification results. Results of tree segmentation by CHM suggest that combining TLS and ULS measurements may improve tree canopy identification. Although ULS is a promising new technology, its applications are clearly limited, at least in mangrove forests such as the Oura River, where Bruguiera gymnorhiza is dominant. Depending on the application, using different LiDAR platforms, such as airborne LiDAR scanning, UAV LiDAR scanning, and TLS, is important. Merging 3D point clouds acquired by different platforms, as proposed in this study, is an important option in this case.

Significance of Geometrical Condition in Preserving the Quality of TLS Measurement

To acquire complete three-dimensional (3D) data that cover the whole surface of the scanned object, multiple scan stations are inevitable. Thus, the registration process is compulsory to oriented TLS multi local coordinate into one global coordinate system. Taking into account the fundamental principle of error propagation in network design, an open network solution for TLS measurement is impacted to yield uncertainties. To investigate this issue this study has been carried out to verify the effect of error propagation in the TLS pre-processing procedure. Two types of network configurations have been established: i. Closed; and ii. Open networks. To measure the accuracies of both configurations, 3D traversing has been performed in establishing six (6) reference points. With the aid of the reference points, the results demonstrated that by neglecting the geometrical condition the accuracy of TLS pre-processed data might be reduced up to 33 percent. To preserve the quality of the final real-world representation derived from TLS measurement, it is advisable to take into account this fundamental principal

Suitability of Aerial Photogrammetry for Dump Documentation and Volume Determination in Large Areas

The study presented in this paper analyses the results of measurements and data processing for documentation and quantification of material in heaps in large areas, where UAVs may no longer be effective due to a large range. Two test heaps were selected from a whole area, where the aim was to confirm the suitability of using the method of digital aerial photogrammetry by manned (crewed) aerial vehicle. For comparison, a commonly used GNSS RTK method was also used. Terrestrial laser scanning was chosen as the control reference method. TLS measurement is a trusted method with high accuracy. The methods were compared with each other through the quality of the mesh, analysis of the cross-sections, and comparison of the volumes of heaps. As a result, the determination of heap volumes and documentation using digital aerial photogrammetry can be confirmed as an appropriate, efficient, fast, and accurate method. The difference in the detected volume was less than 0.1%, the mean difference of the meshes was less than 0.01 m, and the standard deviation was less than 0.05 m.

MONITORING TERRAIN DEFORMATIONS CAUSED BY UNDERGROUND MINING USING UAV DATA

Abstract. Underground mining causes terrain surface deformations that lead to various threats to the environment and people, thus a systematic deformation monitoring needs to be performed. This monitoring mainly focuses only on the vertical part of the deformation and remote sensing techniques are currently very often used for this purpose. The development of Unmanned Aerial Systems (UASs) open new possibilities in this context. Most commonly, the mapping UASs are equipped with RGB cameras but also other lightweight sensors are utilized. In this work, the usefulness of UAS photogrammetry and LiDAR data is investigated in the context of detection and measurement of terrain deformations caused by underground mining. The accuracy of the methods was compared in reference to TLS data. The UAS and TLS measurements were performed in 2018 and 2019 but the subsidence was also evaluated in regards to ALS data acquired in 2011. The standard methodology based on Digital Terrain Models of Difference (DoDs) was applied to detect the subsidence. The DoD analysis was restricted to the hard surfaces. The profiles along the roads were also analysed to validate the accuracy of the data. The analysis showed that the UAS photogrammetry enables to obtain less noisy data and more accurate results of the terrain subsidence measurement than the UAS LiDAR sensors. The comparison of the DoDs showed about 33 cm subsidence between 2011 and 2018, which gives a subsidence rate of about 5 cm/year. The observed subsidence between years 2018 and 2019 was equal to about 5 to 15 cm depending on the measurement technique and investigated area.

Use of TLS (LiDAR) for Building Diagnostics with the Example of a Historic Building in Karlino

This article presents the use of TLS (LiDAR) measurement for the evaluation of the technical conditions of a historic building. A FARO M70 laser scanner was used in the study. The measurements was taken as an RCP point cloud. The measurement allowed to partially determine the cause of the building damage. The performed measurement allows to propose a precise solution that could be pre-fabricated. The study shows the usefulness of TLS in building diagnostics. Improper measurement could lead to a wrong solution and a certain degree of uncertainty.

АНАЛИЗ ДЕФОРМАЦИЙ ПРОЖЕКТОРНОЙ МАЧТЫ ПРИ ПОМОЩИ НАЗЕМНОГО ЛАЗЕРНОГО СКАНИРОВАНИЯ И МЕТОДА КОНЕЧНЫХ ЭЛЕМЕНТОВ

Актуальность темы обусловлена необходимостью усовершенствования подходов к оценке и прогнозу деформаций высокомачтовых опор. Решение этой задачи сопряжено с многими неопределенностями, такими как недостаточность лабораторных исследований свойств материалов и полевых статических и динамических испытаний подобного рода сооружений, малочисленность аналитических исследований и мониторинговых данных. Представлены первоначальные результаты полевых исследований деформаций прожекторной мачты и численного анализа ее напряженно-деформированного состояния. Целью исследования является оценка напряженно-деформированного состояния грунтового основания сооружения и сравнение результатов численного моделирования с данными по деформациям объекта, полученными в ходе лазерного сканирования. Объект – напряженно-деформированное состояние грунтового основания прожекторной мачты на Ванкорском нефтяном месторождении. Методика. Исходными данными для моделирования поведения сооружения послужили данные рекогносцировочного обследования участка. Для характеристики напряженно-деформированного состояния сооружения использовался программный комплекс на базе МКЭ. Для оценки деформаций и построения точной трехмерной модели объекта использовалась технология лазерного сканирования. Сканирование объекта проводилось лазерным 3D сканером Leica Scanstation C10, планово-высотное обоснование и привязка пунктов обоснования к местной системе координат с использованием электронного тахеометра LEICA TS15 и GNSS приемника LEICA GS10, обработка массива точек проводилась в программном комплексе Leica Cyclone 8.0, трехмерное моделирование объекта было осуществлено в программном комплексе SolidWorks. Результаты. Оценено напряженно-деформированное состояние грунтового основания. Создана цифровая расчетная модель. Выполнено сравнение результатов моделирования с пространственно-координатным положением конструкций, установленным при лазерном сканировании. Оценен вклад грунтовых условий в деформации сооружения.

Influence of the simplified stochastic model of TLS measurements on geometry-based deformation analysis

Abstract Terrestrial laser scanners (TLS) are powerful instruments that can be employed for deformation monitoring due to their high precision and spatial resolution in capturing 3D point clouds. Deformation detections from scatter point clouds can be based on different comparison methods, among which the geometry-based method is one of the most popular. Compared with approximating surfaces with predetermined geometric primitives, such as plane or sphere, the B-splines surface approximation offers a great flexibility and can be used to fit nearly every object scanned with TLS. However, a variance-covariance matrix (VCM) of the observations involved in approximating the scattered points to B-spline surfaces impact the results of a congruency test, which is the uniformly most powerful invariant (UMPI) test for discriminating between the null hypothesis of zero deformation and its alternative hypotheses. Consequently, simplified stochastic models may weaken the UMPI property. Based on Monte Carlo simulations, the impact of the heteroscedasticity and mathematical correlations often neglected in B-splines approximation are investigated. These correlations are specific in approximating TLS measurements when the raw measurements are transformed into Cartesian coordinates. The rates of rejecting the null hypothesis in a congruency test is employed to reflect the impact of unspecified VCMs on the power of the congruency test. The rejection rates are not sensitive to the simplification of the stochastic models, in the larger deformation area with higher point accuracy, while they are obviously influenced in the smaller deformation area with unfavourable geometries, i. e. larger uncertainties. A threshold ratio of estimated differences to the relative standard deviation highlights whereas the results of congruency test are reliable when using simplified VCMs. It is concluded that the simplification of the stochastic model has a significant impact on the power of the congruency test, especially in the smaller deformation area with larger uncertainties.

Utilizarea scanerului laser terestru în măsurătorile forestiere: cerințe metodologice și precauții necesare la aplicarea în practică

TLS is also known as ground-based LiDAR which provides the capacity to recreate the 3D vegetation structure with millimeter accuracy. The distance measurement of terrestrial laser scanner Z+F Imager 5010 is based on phase shift measurements which is more accurate than time of flight TLS. The time required for a single scan varies according to the resolution needed. In forestry, TLS is used for the detailed structured modelling of plots and individual trees. Terrestrial laser scanning of trees has been seen as the best alternative to indirect and direct (destructive) measurements of volume. TLS technique provides accurate estimates the location, DBH and tree height from point cloud and besides these measurements can be determined the volume on segments, commercial volume or crown volume. The quality of these metrics depends on the original scan data and their co-registration. We have done TLS measurements in six plots from FundivEurope research project with different slopes, tree density and species composition. The measurements allow us to identify which are advantages and disadvantages of using TLS in forest inventory, but in particular this study draws the attention to the precautions required for an accurate TLS use in biomass estimation.

Influence of scanning parameters on the estimation accuracy of control points of B-spline surfaces

Abstract This contribution deals with the influence of scanning parameters like scanning distance, incidence angle, surface quality and sampling width on the average estimated standard deviations of the position of control points from B-spline surfaces which are used to model surfaces from terrestrial laser scanning data. The influence of the scanning parameters is analyzed by the Monte Carlo based variance analysis. The samples were generated for non-correlated and correlated data, leading to the samples generated by Latin hypercube and replicated Latin hypercube sampling algorithms. Finally, the investigations show that the most influential scanning parameter is the distance from the laser scanner to the object. The angle of incidence shows a significant effect for distances of 50 m and longer, while the surface quality contributes only negligible effects. The sampling width has no influence. Optimal scanning parameters can be found in the smallest possible object distance at an angle of incidence close to 0° in the highest surface quality. The consideration of correlations improves the estimation accuracy and underlines the importance of complete stochastic models for TLS measurements.

ANALYSIS OF RIVER BANK EROSION BY COMBINED AIRBORNE AND LONG-RANGE TERRESTRIAL LASER SCANNING: PRELIMINARY RESULTS ON THE VISTULA RIVER

In our study, high-resolution digital elevation models (HRDEM) were generated by combining the data from airborne laser scanning (ALS, 2012) and long-range terrestrial laser scanning (TLS, 2015) and used for qualitative and quantitative analysis of recent morphodynamic processes in the Vistula river bed near Nieszawa, Central Poland. The study area was a river stretch nearly 1 km long, in its lowland part, with the 440 m wide channel and 3.5‑5.0 m high banks. It is located 27 km downstream from the reservoir in Wloclawek, so it is under the influence of the reservoir. The TLS measurements were performed from the opposite bank of the river, from a distance of up to 750 m. By combining the ALS and TLS data, we investigated and evaluated both the horizontal variations in the height of the river bank and changes in its profile, with a high resolution of about 900 points/m 2 . Our results show that in this river stretch, both the transverse profile of the river bank and the location of its upper edge have been changed during the three years between the ALS and TLS measurement sessions. The scale of this phenomenon varies from a complete lack of erosion to lowering of the upper edge of the cliff by about 1 m, in some points even up to 2 m. The applied methods allowed us to estimate the area of the observed transformations, in contrast to the conventional methods that enable only analyses in selected transverse sections.

Analysis of power lines span geometry based on TLS measurements

The inventory measurements of utility infrastructure are crucial issues in the field of engineering geodesy. Secure usage of power lines requires to monitor their geometry. According to classical approach to measurements of geometry of overhead power lines, it usually allows only to measure directly. Geodetic methods cannot be applied due to measuring limitations (lack of an appropriate area to conduct a measurement). Currently in engineering geodesy it is becoming more common to use methods of laser scanning as well as Unmanned Aerial Photogrammetric Survey. In the Paper, the procedure of determining of an overhead power line’s geometry is presented on the example of an one span measured with Terrestrial Laser Scanning methods. Field measurements were conducted by using laser scanner. Afterwards the point cloud was processed in order to receive the geometry of conductor. Finally, results were presented is tabular and graphic form.

Analysis of power lines span geometry based on TLS measurements

Analysis of power lines span geometry based on TLS measurements

Reactions to gap emergence: Norway spruce increases growth while European beech features horizontal space occupation – evidence by repeated 3D TLS measurements

Reactions to gap emergence: Norway spruce increases growth while European beech features horizontal space occupation – evidence by repeated 3D TLS measurements

COMPARISON OF TARGET- AND MUTUAL INFORMATON BASED CALIBRATION OF TERRESTRIAL LASER SCANNER AND DIGITAL CAMERA FOR DEFORMATION MONITORING

Abstract. In the current state-of-the-art, geodetic deformation analysis of natural and artificial objects (e.g. dams, bridges,...) is an ongoing research in both static and kinematic mode and has received considerable interest by researchers and geodetic engineers. In this work, due to increasing the accuracy of geodetic deformation analysis, a terrestrial laser scanner (TLS; here the Zoller+Fröhlich IMAGER 5006) and a high resolution digital camera (Nikon D750) are integrated to complementarily benefit from each other. In order to optimally combine the acquired data of the hybrid sensor system, a highly accurate estimation of the extrinsic calibration parameters between TLS and digital camera is a vital preliminary step. Thus, the calibration of the aforementioned hybrid sensor system can be separated into three single calibrations: calibration of the camera, calibration of the TLS and extrinsic calibration between TLS and digital camera. In this research, we focus on highly accurate estimating extrinsic parameters between fused sensors and target- and targetless (mutual information) based methods are applied. In target-based calibration, different types of observations (image coordinates, TLS measurements and laser tracker measurements for validation) are utilized and variance component estimation is applied to optimally assign adequate weights to the observations. Space resection bundle adjustment based on the collinearity equations is solved using Gauss-Markov and Gauss-Helmert model. Statistical tests are performed to discard outliers and large residuals in the adjustment procedure. At the end, the two aforementioned approaches are compared and advantages and disadvantages of them are investigated and numerical results are presented and discussed.

Tree stems from terrestrial laser scanner measurements

Abstract Terrestrial laser scanner (TLS) measurements were carried out in mature birch, pine, and spruce stands in Järvselja, Estonia. The structure of stands has been previously studied. A simple special clustering procedure is developed for automatic detection of stem positions and estimation of tree stem dimensions from the TLS point cloud. Tree stem diameter at breast height (DBH), vertical profile of stem and size distribution of DBH is estimated with high precision in the pine stand where the second growth tree layer is almost missing. The presence of second growth limits estimating stem dimensions accurately in the birch stand, and the procedure fails in the dense spruce stand of rich undergrowth and low dead branches. In such stands the TLS measurements should be done in dense grid with short-range sounding setup only. The developed procedure is undemanding for computers and can be applied on simple PC-s.

Spatial and temporal variations in rockfall determined from TLS measurements in a deglaciated valley, Switzerland

AbstractSteep U‐shaped valleys produced by glaciation are commonly eroded by rockfall. In this study we investigate modern and long‐term (power law predicted) rates of rock wall retreat in a deglaciated valley. Our emphasis is on the 5.2 km2 calcareous cliffs covering in the Lauterbrunnen Valley, Switzerland. Terrestrial laser scans were collected during nine field campaigns over 18 months to provide a continuous coverage of most of the valley walls. Results indicate a total of 122 rockfalls with volumes ranging between 0.06 ± 0.01 and 119.34 ± 1.07 m3. Different size groups of rockfall events were correlated with environmental factors (e.g., freeze‐thaw cycles/temperature, precipitation, and seismicity) using a linear regression with variable lag times of 0–6 months. The highest correlation factor (r = 0.6, P = 0.08, 90% significance level) is observed for freeze‐thaw cycles and rockfall events smaller than 1 m3 with a 2 month delay between temperature extremes and rockfall. Frequency‐magnitude relationships for rockfall events were calculated to predict less frequent larger rockfall events that did not occur during the observation period. A Monte Carlo analysis was applied to the frequency‐magnitude relationship to evaluate the sensitivity of results to their stochastic nature. An average power law exponent of 1.71 ± 0.09 was calculated using linear regression. The calculated exponents are similar to other studies in calcareous rock settings conducted over different observation durations. Finally, we determine an average total eroded volume of m3/yr and a corresponding long‐term (power law predicted) cliff retreat rate of .

LiDAR based biomass and crop nitrogen estimates for rapid, non-destructive assessment of wheat nitrogen status

Optical remote sensing of crop nitrogen (N) status is developing into a powerful diagnostic tool that can improve N management decisions. Crop N status is a function of dry mass per unit area (W in tha−1) and N concentration (%Na), which can be used to calculate N nutrition index (NNI), where NNI is %Na/%Nc (%Na is actual N concentration and %Nc is the minimum N concentration required for maximum growth). Using optical remote sensing to estimate crop N status is particularly important during the critical early crop developmental stages when reliable data could still guide effective in-season N fertilizer management decisions (e.g., by adding topdressed fertilizer). However, because the spectral signal measured by traditional optical remote sensing devices during early crop development is often dominated by soil spectral reflectance, early season estimates of W and %Na are prone to large errors. Terrestrial LiDAR (light detection and ranging) scanning (TLS) may alleviate errors as fine scale TLS point data can be used to directly quantify physical W proxies (e.g., crop height or volume) and derive %Na from green (532nm) TLS point return intensity. We evaluated the potential of TLS to assess W, %Na and NNI of winter wheat (Triticum aestivum L.). Green TLS measurements were obtained for two seasons during tillering and jointing. Strong (r2>=0.72, RMSE≤0.68tha−1) relationships occurred between observed W and TLS-derived vegetation volume across all growth stages and seasons. A wider range of relationships existed between %Na and green laser return intensity (r2=0.10–0.75, RMSE=0.31–0.63%). When fused to calculate a TLS based NNI, a moderately strong relationship occurred (r2=0.45–0.54, RMSE=0.11 NNI). Our results demonstrate that green TLS can provide useful information for improving N management during early season wheat growth.

Green-wavelength terrestrial laser scanning of mountain channel

Abstract. It is crucial to understand and predict how the water and sediment flow in mountain channels for better disaster risk management. Detailed and quantitative measurement of channel and stream-bed structure is in great demand. In this paper, the utility of greenwavelength TLS for measurement of submerged stream-bed is preliminary examined in a steep mountain channel. The ability of through water measurement is evaluated in terms of water depth and flow velocity. Automated extraction of submerged objects is also tested. The results of comparison of water depth derived by TLS and survey displayed significant correlation between them, presenting good performance of green-wavelength TLS for measurement of submerged stream-bed. The analysis using a Generalized Liner Model (GLM) indicated that each of water depth and flow velocity alone does not affect the accuracy of TLS measurement, however, the interaction between water depth and flow velocity may have an influence. The attempt to automatically extract the dimension of submerged objects was partially successful, achieving maximum error of +0.8 cm for two objects.

Comparison of Terrestrial and Airborne LiDAR in Describing Stand Structure of a Thinned Lodgepole Pine Forest

Airborne LiDAR (ALS) has been widely used for measuring canopy structure, but much of the woody components of the canopy are not directly visible with this system. Terrestrial LiDAR (TLS) data may help fill this gap by helping to understand the relationship between above- and below-canopy architecture. In this study, we report on the potential for combining TLS and ALS, thereby focusing on forest inventory and wood quality?related characteristics (such as number and dimension of branches). Our results show that both TLS and ALS were able to describe stand height using the top 10% of LiDAR returns at a high level of precision; however, TLS measurements were negatively biased by approximately 1 m (R 2 = 0.96 and 0.86 for ALS and TLS, respectively; P < 0.05). The distribution of foliage measured by ALS and TLS was strongly related to basal area (R 2 = 0.63 and 0.91 for ALS and TLS, respectively) and stand density (R 2 = 0.89 and 0.72 for ALS and TLS, respectively). Tree-level attributes were more accurately described by TLS (R 2 = 0.63) compared with ALS (R 2 = 0.37) for crown depth and a similar result applied to dbh with R 2 = 0.63 for TLS versus R 2 = 0.43 for ALS.