Terrestrial Laser Scanning Surveys Research Articles

Viewshed simulation and optimization for digital terrain modelling with terrestrial laser scanning

ABSTRACT The main objective of this study is the development of a simulation and optimization method for wide-area terrain mapping with terrestrial laser scanning (TLS). The problem can be stated as follows: given a prior digital surface model (DSM) of a region of interest (e.g. from airborne lidar or structure-from-motion photogrammetry), determine the minimum number of scan locations required to seamlessly scan the terrain in the region for a given scanner range and angular field-of-view (FOV). An optimization method for measurement setup is developed using multiple viewshed analysis and simulated annealing (SA) constrained by the system performance characteristics and survey specifications. The method is evaluated at a sediment and erosion control facility with hilly terrain by comparing random scan locations versus optimized three to six scan locations. Statistical results illustrate that average visibility for random sampling increases gradually with scan locations. However, random sampling clearly underperforms in terms of scan visibility relative to five or six optimized scan locations with an average visibility of 100%. Similar patterns in optimized scan locations demonstrate that certain terrain morphometry at the study site is an essential factor for TLS survey design. Finally, an optimized solution is compared to a brute-force manual solution for determining four scan locations for conducting surveys at the study site. Results show the effectiveness of the optimization method for selecting combinations of scan locations that enable more efficient TLS survey coverage over a wider terrain area compared to manual selection. Furthermore, results demonstrate the adaptability of the method to take into consideration different scan parameters and survey conditions, such as pre-determined scan locations that may be required (e.g. a survey control monument).

The First Video Witness of Coastal Boulder Displacements Recorded during the Impact of Medicane “Zorbas” on Southeastern Sicily

Over the last few years, several authors have presented contrasting models to describe the response of boulders to extreme waves, but the absence of direct observation of movements has hindered the evaluation of these models. The recent development of online video-sharing platforms in coastal settings has provided the opportunity to monitor the evolution of rocky coastlines during storm events. In September 2018, a surveillance camera of the Marine Protected Area of Plemmirio recorded the movement of several boulders along the coast of Maddalena Peninsula (Siracusa, Southeastern Sicily) during the landfall of the Mediterranean tropical-like cyclone (Medicane) Zorbas. Unmanned autonomous vehicle (UAV) photogrammetric and terrestrial laser scanner (TLS) surveys were performed to reconstruct immersive virtual scenarios to geometrically analyze the boulder displacements recorded in the video. Analyses highlighted that the displacements occurred when the boulders were submerged as a result of the impact of multiple small waves rather than due to a single large wave. Comparison between flow velocities obtained by videos and calculated through relationships showed a strong overestimation of the models, suggesting that values of flow density and lift coefficient used in literature are underestimated.

Mechanisms and frequency-size statistics of failures characterizing a coastal cliff partially protected from the wave erosive action

Landslides and surface erosion are major processes controlling the progressive recession of many rocky cliffs along the Italian coastline. Nevertheless, many coastal settlements were built along cliffed sectors prone to rapid collapses. This represents a serious risk for tourists and living people, as well as for buildings, roads and railway networks. The densely urbanized coastline of the Campi Flegrei active volcanic district is one of the rocky coastal areas of South Italy mostly exposed to the recession. Here, coastal cliffs are made by volcaniclastic deposits and include remnants of ancient volcanic edifices formed in the last 15 ka. Due to petrographic, geotechnical and geostructural properties of volcaniclastic deposits, these cliffs have been affected by rapid recession since their origin. This research focuses on a cliff of the Campi Flegrei coastaline (Torrefumo, Monte di Procida) which, although currently protected from the sea waves by a seawall, is still retreating. We assessed the ongoing recession using a change detection analysis, based on accurate topographic data acquired with two terrestrial laser scanning surveys executed in 2013 and 2016. The quantitative comparison of 3D point clouds datasets allowed detecting 191 cliff failures. We verified that the frequency-magnitude distribution of the detached blocks followed an inverse power law, and most of the involved volumes were between 0.01 and 1 m3. Retreat rates of different cliff sectors varied from 0.001 to 0.025 m/year. Our analysis also allowed us to recognize slope failure mechanisms and distinguish rock falls from grain-by-grain surficial erosion.

From TLS data to FE model: a workflow for studying the dynamic behavior of the Pulpit by Giovanni Pisano in Pistoia (Italy)

This paper discusses the first results of an ongoing two-year research activity aimed to identify the actual dynamic behavior of the Pulpit of Giovanni Pisano in Pistoia in order to design a long-term structural health monitoring system. First steps of the research have foreseen a Photogrammetric and Terrestrial Laser Scanner (TLS) survey of the structure in order to build a refined digital three-dimensional geometric model of the Pulpit to be employed for both documentation and structural assessment. The paper reports the main outcomes of the TLS survey together with the procedure employed to obtain a reliable finite element model of the Pulpit. An original workflow for direct transfer of high accuracy TLS-based three-dimensional model to a finite element model is proposed and discussed.

Remarks on the Proportions and Dimensions Used in the Design of the Medieval Church of Zsámbék

Since the 19th century, the church of Zsámbék was continuously a focus of scholars' interest. The present paper intends to research the church ruins with a new aspect. Using an accurate terrestrial laser scan survey, the geometry of the plan is analysed in order to find proportions among the dimensions. The main goal of the study is to gather information about the design logic of the first masters of the 13th-century Premonstratensian abbey. In addition, our goal was to detect contributions to the 13th-century construction history of the church, that cannot be found in archives of graphic sources. The latest archaeological excavation achieved excellent results concerning several crucial historical points; however, the periodization of the church is still not entirely clarified. From the 19th century, different scholars have proposed various hypotheses about this topic, without consensus.

Three‐dimensional reconstruction of fluvial surface sedimentology and topography using personal mobile laser scanning

AbstractHigh‐resolution quantification of fluvial topography has been enabled by a number of geomatics technologies. Hyperscale surveys with spatial extents of <1 km2 have been widely demonstrated by means of terrestrial laser scanning (TLS) and structure‐from‐motion (SfM) photogrammetry. Recent advances in the development and integration of global navigation satellite system (GNSS), inertial measurement unit (IMU) and lightweight laser scanning technologies are now resulting in the emergence of personal mobile laser scanners (MLS) that have the potential to increase data acquisition and processing rates by one to two orders of magnitude compared to TLS/SfM, and thus challenge the recent dominance of these technologies. This investigation compares a personal MLS survey using a Leica Pegasus Backpack that integrates Velodyne Puck VLP‐16 sensors, and a multi‐station static TLS survey using a Riegl VZ‐1000 scanner, to produce digital elevation models (DEMs) and surface sedimentology maps. The assessment is undertaken on a 500 m long reach of the braided River Feshie. Comparison to 107 independent real‐time kinematic (RTK)‐GNSS check points resulted in similar mean error (ME) and standard deviation error (SDE) for TLS (ME = −0.025 m; SDE = 0.038 m) and personal MLS (ME = −0.014 m; SDE = 0.019 m). Direct cloud‐to‐cloud (C2C) comparison between a sample of TLS and personal MLS observations (2.8 million points) revealed that C2C distances follow a sharply decreasing Burr distribution (a = 2.35, b = 3.19, rate parameter s = 9.53). Empirical relationships between sub‐metre topographic variability and median sediment grain size (10–100 mm) demonstrate that surface roughness from personal MLS can be used to map median grain size. Differences between TLS and personal MLS empirical relationships suggest such relationships are dependent on survey technique. Personal MLS offers distinct logistical advantages over SfM photogrammetry and TLS for particular survey situations and is likely to become a widely applied technique. © 2019 John Wiley & Sons, Ltd.

Discontinuity Mapping using Terrestrial Laser Scanner and Kinematic Method

This study presents the results of discontinuity mapping using terrestrial laser scanning (TLS) survey and the kinematic method. The results provide the current site and slope condition of comprehensive geological study using terrestrial laser scanning and discontinuity survey at Simpang Pulai, Perak. From the results obtained, it can be concluded that the major potential failures in this area are wedge and plane failures, but there are some area had the potential of toppling failure. This study, however, constitutes a preliminary design consideration and not intended for use in final design or construction. The final design shall be made by the engineer based on the further detail site investigation (S.I.) and other design factors to be used in the actual design of the project.

EXTRACTION OF MAIN LEVELS OF A BUILDING FROM A LARGE POINT CLOUD

Abstract. Horizontal levels are references entities, the base of man-made environments. Their creation is the first step for various applications including the BIM (Building Information Modelling). BIM is an emerging methodology, widely used for new constructions, and increasingly applied to existing buildings (scan-to-BIM). The as-built BIM process is still mainly manual or semi-automatic and therefore is highly time-consuming. The automation of the as-built BIM is a challenging topic among the research community. This study is part of an ongoing research into the scan-to-BIM process regarding the extraction of the principal structure of a building. More specifically, here we present a strategy to automatically detect the building levels from a large point cloud obtained with a terrestrial laser scanner survey. The identification of the horizontal planes is the first indispensable step to produce an as-built BIM model. Our algorithm, developed in C++, is based on plane extraction by means of the RANSAC algorithm followed by the minimization of the quadrate sum of points-plane distance. Moreover, this paper will take an in-depth look at the influence of data resolution in the accuracy of plane extraction and at the necessary accuracy for the construction of a BIM model. A laser scanner survey of a three floors building composed by 36 scan stations has produced a point cloud of about 550 million points. The estimated plane parameters at different data resolution are analysed in terms of distance from the full points cloud resolution.

Sensor-Based Optimization of Terrestrial Laser Scanning Measurement Setup on GPU

A novel formulation of the set cover problem is presented to find the optimal placement of the scan stations in a terrestrial laser scanning survey. The problem is formulated in 2-D by including sensor-based constraints such as coverage and overlap. The coverage constraint ensures a minimum density of horizontal scan lines on the ground. The overlap constraint enables automatic scan alignment and registration. The optimization problem takes into account both environment occlusions and a maximum allowed incidence angle of the laser beams. The adopted laser model includes fixed parameters such as laser height, angular resolution, field of view, and minimum and maximum sensor range. The sensor placement problem is solved using a numerical approach implemented on graphics processing unit (GPU). Thanks to the GPU acceleration, experiments have been performed in large-scale environments with internal structures.

GRAPHICAL DATA FLOW BASED IN TLS AND PHOTOGRAMMETRY FOR CONSOLIDATION STUDIES OF HISTORICAL SITES. THE CASE STUDY OF JUROMENHA FORTRESS IN PORTUGAL

Abstract. This paper discusses the graphical data flow, based on terrestrial laser scanning (TLS) and photogrammetry, for the conservation and rehabilitation project of the Fortress of Juromenha, located nearby the Portuguese-Spanish border in the Alentejo Province. First, we describe the strategy of data acquisition including GPS positioning, drone imagery, ground based imagery, and TLS survey. For the data input, this study considers two types of natures: quantitative and qualitative. Quantitative means anything that can be quantified such as a measurement, an orthoimage, a point cloud or a 3D model. Qualitative means more intangible information such as a perspective on the state of conservation of a surface, a texture, or an ambience. Second, we illustrate the processing step highlighting the challenges and defining the outcomes. Next, it is detailed what kind of data was extracted to prepare the basis for the documents to be used on the conservation project. This section is complemented with the analysis on how data was shared among the project team and how it was used. Finally, it is discussed how the nature of the data and information generated influenced the consolidation design.

3D RECONSTRUCTION OF THE ROMAN DOMUS IN THE ARCHAEOLOGICAL SITE OF LYLIBAEUM (MARSALA, ITALY)

Abstract. Generally, terrestrial laser scanning surveys involve a rather large number of scans to ensure a high percentage of overlap required for the scan registration phase (target-based or point-based registration, cloud-to-cloud registration). These approaches result in data redundancy that could slow down both the acquisition and post-processing phases. In recent years, the technological evolution in the field of laser scanners has been directed to the development of devices that are able to perform an onsite pre-registration, to optimize the survey procedures and the reliability of the registration of the scan. The paper presents the results achieved during a terrestrial laser scanning survey carried out for the documentation and 3D reconstruction of the large and complex archaeological remains of the so-called Roman Domus in the archaeological site of Lylibaeum (Marsala, Italy). The survey was also conducted using a terrestrial laser scanner capable of pre-registering scans using a topographic approach. The pre-registration procedure and the data acquisition strategy have allowed to optimize the workflow and to obtain a 3D model of the Roman Domus with a high level of detail and area coverage.

Comparing sUAS Photogrammetrically-Derived Point Clouds with GNSS Measurements and Terrestrial Laser Scanning for Topographic Mapping

Interest in small unmanned aircraft systems (sUAS) for topographic mapping has significantly grown in recent years, driven in part by technological advancements that have made it possible to survey small- to medium-sized areas quickly and at low cost using sUAS aerial photography and digital photogrammetry. Although this approach can produce dense point clouds of topographic measurements, they have not been tested extensively to provide insights on accuracy levels for topographic mapping. This case study examines the accuracy of a sUAS-derived point cloud of a parking lot located at the Citizens Bank Arena (CBA) in Ontario, California, by comparing it to ground control points (GCPs) measured using global navigation satellite system (GNSS) data corrected with real-time kinematic (RTK) and to data from a terrestrial laser scanning (TLS) survey. We intentionally chose a flat surface due to the prevalence of flat scenes in sUAS mapping and the challenges they pose for accurately deriving vertical measurements. When the GNSS-RTK survey was compared to the sUAS point cloud, the residuals were found to be on average 18 mm and −20 mm for the horizontal and vertical components. Furthermore, when the sUAS point cloud was compared to the TLS point cloud, the average difference observed in the vertical component was 2 mm with a standard deviation of 31 mm. These results indicate that sUAS imagery can produce point clouds comparable to traditional topographic mapping methods and support other studies showing that sUAS photogrammetry provides a cost-effective, safe, efficient, and accurate solution for topographic mapping.

A Rapid Terrestrial Laser Scanning Method for Coastal Erosion Studies: A Case Study at Freeport, Texas, USA.

Terrestrial laser scanning (TLS) has become a powerful data acquisition technique for high-resolution high-accuracy topographic and morphological studies. Conventional static TLS surveys require setting up numerous reflectors (tie points) in the field for point clouds registration and georeferencing. To reduce surveying time and simplify field operational tasks, we have developed a rapid TLS surveying method that requires only one reflector in the field. The method allows direct georeferencing of point clouds from individual scans to an East–North–Height (ENH) coordinate system tied to a stable geodetic reference frame. TLS datasets collected at a segment of the beach–dune–wetland area in Freeport, Texas, USA are used to evaluate the performance of the rapid surveying method by comparing with kinematic GPS measurements. The rapid surveying method uses two GPS units mounted on the scanner and a reflector for calculating the northing angle of the scanner’s own coordinate system (SOCS). The Online Positioning User Service (OPUS) is recommended for GPS data processing. According to this study, OPUS Rapid-Static (OPUS-RS) solutions retain 1–2 cm root mean square (RMS) accuracy in the horizontal directions and 2–3 cm accuracy in the vertical direction for static observational sessions of approximately 30 min in the coastal region of Texas, USA. The rapid TLS surveys can achieve an elevation accuracy (RMS) of approximately 3–5 cm for georeferenced points and 2–3 cm for digital elevation models (DEMs). The elevation errors superimposed into the TLS surveying points roughly fit a normal distribution. The proposed TLS surveying method is particularly useful for morphological mapping over time in coastal regions, where strong wind and soft sand prohibit reflectors from remaining strictly stable for a long period. The theories and results presented in this paper are beneficial to researchers who frequently utilize TLS datasets in their research, but do not have opportunities to be involved in field data acquisition.

Evolution of Debris‐Flow Initiation Mechanisms and Sediment Sources During a Sequence of Postwildfire Rainstorms

Wildfire alters vegetation cover and soil hydrologic properties, substantially increasing the likelihood of debris flows in steep watersheds. Our understanding of initiation mechanisms of postwildfire debris flows is limited, in part, by a lack of direct observations and measurements. In particular, there is a need to understand temporal variations in debris‐flow likelihood following wildfire and how those variations relate to wildfire‐induced hydrologic and geomorphic changes. In this study, we use a combination of in situ measurements, hydrologic monitoring equipment, and numerical modeling to assess the impact of wildfire‐induced hydrologic and geomorphic changes on debris‐flow initiation during seven postwildfire rainstorms. We predict the impact of hillslope erosion on debris‐flow initiation by combining terrestrial laser scanning surveys of a hillslope burned during the 2016 Fish Fire with numerical modeling of sediment transport throughout a 0.12‐km2 basin in southern California. We use measurements of sediment thickness within the channel to constrain numerical experiments and to assess the role of channel sediment supply on debris‐flow initiation. Results demonstrate that debris flows initiated during rainstorms where hillslopes contributed minimally to the event sediment yield and suggest that large inputs of sediment from rill and gully networks are not essential for runoff‐generated debris flows. Simulations suggest that both the gradual entrainment of sediment and the mass failure of channel bed sediment can increase sediment concentration to levels associated with debris flows. Finally, postwildfire debris‐flow initiation appears closely linked to the same rainfall intensity‐duration threshold despite temporal changes in the sediment source, initiation processes, and hydraulic roughness.

GEOMATICS IN BRIDGE STRUCTURAL HEALTH MONITORING, INTEGRATING TERRESTRIAL LASER SCANNING TECHNIQUES AND GEOTECHNICAL INSPECTIONS ON A HIGH VALUE CULTURAL HERITAGE

Abstract. The paper presents preliminary findings from a research study designed to assess the health status of a medieval bridge built on 1500 under the Medici dynasty over the river Sieve, close to Florence. The structure, a two span stone bridge with a main central pillar, experienced some restructuring interventions from 1555 to the present. The left span has been closed for some decades, and for many years the water has been allowed to float under it in case of severe flood only. At the beginning of year 2000 the left span has been opened to the regular flux of water. After opening, a maelstrom has been noticed as permanently present at the main pier’s basis highlighting the presence of a fracture in the concrete base around the central pile of the bridge. In order to investigate structural health and to assess bridge’s stability structural inspections and hydraulic surveys have been carried out. This manuscript reports Terrestrial Laser Scanning (TLS) survey results. Surface comparisons to identify anomalies and defromations have been carried out by exploiting Two TLS campaigns that were performed within a 6 years time span.

An Accurate TLS and UAV Image Point Clouds Registration Method for Deformation Detection of Chaotic Hillside Areas

Deformation detection determines the quantified change of a scene’s geometric state, which is of great importance for the mitigation of hazards and property loss from earth observation. Terrestrial laser scanning (TLS) provides an efficient and flexible solution to rapidly capture high precision three-dimensional (3D) point clouds of hillside areas. Most existing methods apply multi-temporal TLS surveys to detect deformations depending on a variety of ground control points (GCPs). However, on the one hand, the deployment of various GCPs is time-consuming and labor-intensive, particularly for difficult terrain areas. On the other hand, in most cases, TLS stations do not form a closed loop, such that cumulative errors cannot be corrected effectively by the existing methods. To overcome these drawbacks, this paper proposes a deformation detection method with limited GCPs based on a novel registration algorithm that accurately registers TLS stations to the UAV (Unmanned Aerial Vehicle) dense image points. First, the proposed method extracts patch primitives from smoothed hillside points, and adjacent TLS scans are pairwise registered by comparing the geometric and topological information of or between patches. Second, a new multi-station adjustment algorithm is proposed, which makes full use of locally closed loops to reach the global optimal registration. Finally, digital elevation models (DEMs, a DEM is a numerical representation of the terrain surface, formed by height points to represent the topography), slope and aspect maps, and vertical sections are generated from multi-temporal TLS surveys to detect and analyze the deformations. Comprehensive experiments demonstrate that the proposed deformation detection method obtains good performance for the hillside areas with limited (few) GCPs.

Registration of Terrestrial Laser Scanning Surveys Using Terrain-Invariant Regions for Measuring Exploitative Volumes over Open-Pit Mines

Terrestrial laser scanning (TLS) techniques have been widely used in open-pit mine applications. It is a crucial task to measure the exploitative volume of open-pit mines, within a specific time interval. One major challenge is posed, however, when conducting accurate registrations for temporal TLS surveys in continuously changing areas, created by excavation activities. In this paper, we propose a coarse-to-fine registration method, based on terrain-invariant regions (TIR), for temporal TLS surveys. More specifically, an approximate four-point congruent set (4PCS) of temporal TLS surveys is first identified, based on affine invariant rules. Second, a set of correspondences among temporal TLS surveys were collected by matching multi-scale sparse features of the 3D neighbors, centered at the approximate 4PCS. Third, the correspondences were used to estimate a rigid motion between the overlapping TLS surveys for the coarse registration, according to which the initial TIR from temporal TLS surveys were identified. Finally, the rigid motion between temporal TLS was iteratively optimized, based on the point clouds, only from the TIR. Based on the fine-level registered TLS surveys, Digital Elevation Models (DEMs) can be generated to calculate the exploitative volume, through a DEM differential. We applied the proposed method to two open-pit mines in China, and also compared our method with five state-of-the-art methods for registering temporal TLS surveys. Experimental results indicated that the proposed method achieved a higher registration accuracy than the state-of-the-art methods. Based on the registered result, our method achieved a 98.03% overall accuracy for measuring the exploitative volume, compared to in-situ measurement.

Detection and geometric characterization of rock mass discontinuities using a 3D high-resolution digital outcrop model generated from RPAS imagery – Ormea rock slope, Italy

The use of a remotely piloted aircraft system (RPAS) and digital photogrammetry is valuable for the detection of discontinuities in areas where field mapping and terrestrial photogrammetry or laser scanner surveys cannot be employed because the slope is unsafe, inaccessible, or characterized by a complex geometry with areas not visible from the ground. Using the Structure-from-Motion method, the acquired images can be used to create a 3D texturized digital outcrop model (TDOM) and a detailed point cloud representing the rock outcrop. Discontinuity orientations in a complex rock outcrop in Italy were mapped in the field using a geological compass and by manual and automated techniques using a TDOM and point cloud generated from RPAS imagery. There was a good agreement between the field measurements and manual mapping in the TDOM. Semi-automated discontinuity mapping using the point cloud was performed using the DSE, qFacet FM, and qFacet KD-tree methods applied to the same 3D model. Significant discrepancies were found between the semi-automatic and manual methods. In particular, the automatic methods did not adequately detect discontinuities that are perpendicular to the slope face (bedding planes in the case study). These differences in detection of discontinuities can adversely influence the kinematic analysis of potential rock slope failure mechanisms. We use the case study to demonstrate a workflow that can accurately map discontinuities with results comparable to field measurements. The combined use of TDOM and RPAS dramatically increases the discontinuity data because RPAS can supply a good coverage of inaccessible or hidden portions of the slope and TDOM is a powerful representation of the reality that can be used to map discontinuity orientations including those that are oriented perpendicular to the slope.

Integrated methods for documentation and analysis of archaeological heritage: the residential building along the western side of the Canopus at Hadrian’s Villa. Initial results and research perspectives

The paper presents the initial observations on a lesser-known but extremely interesting monument at Hadrian’s Villa, the so-called Tabernae , partly restored and used at present as Antiquarium of refined marble statuary, and partly closed to the public and still under excavation. The building consists of two adjoining structures on high substructures resting on two different levels of the tuff layer. In recent years, on the occasion of some works for the museum, an excavation has brought to light some remains; from then onwards the team has taken an interest in the building built on the upper terraces, proving its rectangular plan with a central courtyard thanks to additional archaeological excavations. Research activities are still ongoing; however, a complete terrestrial laser scanner survey of the whole building has already been started, considering both levels, in order to analyse in depth the remains and the architectural structure of the complex.

3D IMAGE BASED GEOMETRIC DOCUMENTATION OF A MEDIEVAL FORTRESS

Abstract. The detailed and thorough documentation of monuments is a rather complex process that requires the application of the best available state of the art techniques in order to preserve, restore, promote and make cultural heritage accessible to the public. This paper presents the 3D Geometric Documentation of a part of the medieval fortress of Chios, focussing in particular on the practical challenges which the object presented. The case study is a part of the fortified construction, consisting of a bastion, a watch tower on top of this bastion and a significant part of its walls with a surface of about 1053 m2 in total. The goal of the survey was to produce an accurate 3D detailed textured model and a series of coloured orthophotos and 2D vector drawings. The documentation methods employed included close-range automated photogrammetry and image-based modelling, terrestrial laser scanning and topographic surveys, an ideal combination of methods.