Laser Scanning Survey Research Articles

Test of Global Positioning System–Inertial Measurement Unit Performance for Surveying Road Alignment

In an effort to shift road alignment surveying from manual to automatic methods, moving objects—such as a vehicle on which a Global Positioning System–inertial measurement unit (GPS-IMU) is mounted—are being used to perform surveys and obtain more accurate results. Two road alignment survey methods are compared: an affordably priced microelectromechanical system (MEMS) GPS-IMU and a high-priced fiber-optic–type GPS-IMU. Cross-section angle values from a stationary laser scanner survey and a GPS-IMU survey are compared to determine whether the roll attitude value of GPS-IMU can be used to ensure a more accurate comparison of the cross-section angle. In addition, GPS-IMU performance is compared under various test conditions to survey road alignment, and results indicate that the fiber-optic GPS-IMU is needed to ensure accuracy within the 10% margin of error required for road alignment. In a test conducted to verify whether the roll value of a vehicle can be used as is to survey the cross-section angle of a road, the values from GPS-IMU, drawing, and laser were within a 1% margin of error. Thus, it would be possible to use the roll value obtained from a vehicle as is to survey the road cross-section angle accurately.

Multiple Visualization Web Approach for Cultural Heritage Objects

Usually the diffusion and sharing of cultural heritage documented 3D models on the web are not first of concern for scholars due to the fear of losing the intellectual property related to them. Sometimes the interaction and navigation of virtual objects via the World Wide Web is also problematic due to their dimension (number of triangles), when high-definition has to be preserved. In this paper we propose a mash up methodology, for a multiple approach to visualize 3D models over the internet. After the digitization of a marble statue placed in the Medieval Museum of the city of Bologna, according to the well known 3D pipeline (from the laser scan survey to the texturing process), we assembled together different solutions for sharing the model on the web.

Prediction of plot-level forest variables using TerraSAR-X stereo SAR data

Promising results have been obtained in recent years in the use of high-resolution X-band stereo SAR satellite images (with the spatial resolution being in order of meters) in the extraction of elevation data. In the case of forested areas, the extracted elevation values appear to be somewhere between the ground surface and the top of the canopy, depending on the forest characteristics. If the ground surface elevations are known by using a Digital Terrain Model derived from Airborne Laser Scanning surveys, it is possible to obtain information related to forest resources. To the best of our knowledge, this paper, presents the first attempt to obtain forest variables at plot level based on TerraSAR-X stereo SAR images (non-interferometric data). The study set consisted of 109 circular test plots for which forest variables were observed by performing tree-specific measurements. The statistical features were calculated for each test plot from the elevation values extracted from stereo SAR data. This was followed by predicting field-observed plot-level forest variables from the features derived from stereo SAR data using the Nearest Neighbors approach which employs the Random Forest technique in selection of the nearest neighbors. The relative errors (RMSE%) for predicting the stem volume, basal area, mean forest canopy height, and mean diameter values were 34.0%, 29.0%, 14.0%, and 19.7%, respectively. The results indicate that there was no clear saturation level in stem volume estimation. In this case study, stem volumes were predicted up to about 400 m 3/ha. In the light of these results, stereo SAR data appears to be an interesting remote-sensing technique for future forest inventories. For example, stereo SAR data could have high potential in forest inventories as the SAR-based features can be adapted to the methods currently used in inventories.

Laser scanning technology for the hypogean survey: the case of Santa Barbara karst system (Sardinia, Italy)

The morphological knowledge of the territory, bothin its surface and subterranean aspects, is the main premise to all decision-making procedures as well as all planning and management activities. Knowledge takes shape into reliable precise and complete thematic cartography and databases, whichare necessary for anybody dealing withunderground contexts: speleologists, scientists, public administrations, managing authorities etc. Surveys in caves are normally carried out withtraditional techniques and instruments, whichare essential for a first representation but not enoughfor a pragmatic effective topographic approach. Laser scanning technique can be an alternative to the traditional systems. Laser scanning quickly acquires the shape of cavities as “point clouds” (x, y, z coordinates and colour values) and produces a highprecision database of the surveyed object. Laser scanning technology is therefore a feasible way to document caves in a precise exhaustive way, limiting risks relating to lack and/or inadequacy of data. The present paper explains the laser scanning survey carried out in San Giovanni mine near Iglesias (Sardinia, Italy), particularly in Santa Barbara and Santa Barbara 2 caves, the data post-processing and three-dimensional modelling of “point clouds” (operations performed witha dedicated software), and the use of the obtained digital model. Moreover, the paper describes the advantages of laser scanning for the hypogean survey in comparison to traditional methods and the future potentialities of a broad application of laser scanning instruments in caves.

Terrestrial Laser Scanner Resolution: Numerical Simulations and Experiments on Spatial Sampling Optimization

An empirical approach is proposed in order to evaluate the largest spot spacing allowing the appropriate resolution to recognize the required surface details in a terrestrial laser scanner (TLS) survey. The suitable combination of laser beam divergence and spot spacing for the effective scanning angular resolution has been studied by numerical simulation experiments with an artificial target taken from distances between 25 m and 100 m, and observations of real surfaces. The tests have been performed by using the Optech ILRIS-3D instrument. Results show that the discrimination of elements smaller than a third of the beam divergence (D) is not possible and that the ratio between the used spot-spacing (ss) and the element size (TS) is linearly related to the acquisition range. The zero and first order parameters of this linear trend are computed and used to solve for the maximum efficient ss at defined ranges for a defined TS. Despite the fact that the parameters are obtained for the Optech ILRIS-3D scanner case, and depend on its specific technical data and performances, the proposed method has general validity and it can be used to estimate the corresponding parameters for other instruments. The obtained results allow the optimization of a TLS survey in terms of acquisition time and surface details recognition.

Effects of surface irregularities on intensity data from laser scanning: an experimental approach.

The results of an experiment carried out with the aim to investigate the role of surface irregularities on the intensity data provided by a terrestrial laser scanner (TLS) survey are reported here. Depending on surface roughness, the interaction between an electromagnetic wave and microscopic irregularities leads to a Lambertian-like diffusive light reflection, allowing the TLS to receive the backscattered component of the signal. The described experiment consists in a series of TLS-based acquisitions of a rotating artificial target specifically conceived in order to highlight the effects on the intensity data due to surface irregularity. This target is articulated in a flat plate and in an irregular surface, whose macro-roughness has a characteristic length with the same order of the spot size. Results point out the different behavior of the plates. The intensity of the signal backscattered by the planar element decreases if the incidence angle increases, whereas the intensity of the signal backscattered by the irregular surface is almost constant if the incidence angle varies. Since the typical surfaces acquired in a geological/geophysical survey are generally irregular, these results imply that the intensity data can be easily used in order to evaluate the reflectance of the material at the considered wavelength, e.g. for pattern recognition purposes.

Water level and volume estimations of the Albano and Nemi lakes (central Italy)

In April 2006 an airborne laser scanning (LIDAR) survey of the Albano and Nemi craters was carried out to obtain a high resolution digital terrain model (DTM) of the area. We have integrated the LIDAR survey of the craters and the recent bathymetry of the Albano lake to achieve a complete DTM, useful for morphological studies. In addition, with a GPS RTK survey (July 2007) we estimated the Albano and Nemi mean lake levels respectively at 288.16 m and 319.02 m (asl). Based on the integrated DTM and the newly estimated water level values, we evaluated about 21.7·106 m3 the water volume loss of the Albano lake from 1993 to 2007, with an average rate of about 1.6·106 m3/yr.

On the retreat of forested, cohesive riverbanks

Data from the Brandywine Creek in Pennsylvania and the South River in Virginia document spatial and temporal patterns describing the retreat of gently curving bends with forested riparian zones containing a mix of very large and smaller trees, cohesive banks, and slow rates of migration (∼ 0.1 m/yr). Field data include 2.5 years of bank profile surveys, measurements of tree morphology, and ground-based laser scanner (LiDAR) surveys repeated biannually. These banks retreat through a cycle of erosion on decadal timescales. Initially, small volumes (mean = 0.173 m 3 per bank erosion event) of soil are removed between large trees growing on the bank. Near trees, the rate of bank retreat is initially negligible, creating a scalloped bank morphology buttressed by large trees. As the trees are increasingly exposed to the flow, they become slowly undercut, gradually leaning into the channel and sliding down to the toe of the bank, eventually toppling into the river after a few years, which restarts the cycle. A magnitude–frequency analysis of monitoring data from the Brandywine Creek indicates that the effective bank erosion event only 0.11 m 3; thus, forested bank retreat is dominated by small soil failures. Large erosion events, many associated with trees toppling into the river, greatly increase the variance of time-averaged rates of bank erosion, such that almost 4 years of monitoring are needed to measure time-averaged rates of erosion to within an accuracy of 10%. Because of the limited spatial extent of our survey data and the absence of large discharges, these results are provisional. Improved process-based models to predict the retreat of forested riverbanks should account for the spatial structure of riparian forests and the interactions between the flow, the gradual removal of bank soils, and the ongoing efforts of the trees to remain attached to the bank.

Modelling masonry arches shape using terrestrial laser scanning data and nonparametric methods

Since masonry arch is one of the most common structural forms in both historic bridges and in architecture across the world such as domes and vaults, its dimensional and structural analysis is still the subject of numerous investigations. Controlling the deformation in historic arch bridges involves a number of difficulties arising from the measurement technique and the analysis methodology. Important advances have been made on terrestrial laser scanning technology to allow measuring the 3D geometry of objects without making direct contact with them with very high rates of data acquisition, high accuracy and long range. However, the development of computer algorithms to automate the analysis of the clouds of points would be useful to take advantage of the potential of this technique in the field of dimensional and structural analysis of historic bridges. This article presents a methodology to estimate the deformation of arches or vaults based on the symmetry of sections obtained along the vault guideline. The accurate geometry of the arches is obtained by means of a 3D laser scanner survey, and the point cloud is processed by statistical nonparametric methods based on local bivariate kernel smoothers, allowing estimation of arch cross-sections without establishing any parametric shape a priori.

3D laser scanning and the conservation of earthen architecture: a case study at the UNESCO World Heritage Site Merv, Turkmenistan

In the autumn of 2007, a new phase of conservation effort and research was implemented by University College London's Ancient Merv Project (AMP) at the Silk Road cities of Merv, Turkmenistan. The 1200ha archaeological park consists of multiple cities built of earthen architecture and fired brick, of which much of the archaeology is buried, including extensive stretches of defensive circuits of some of the cities. Many of the exposed structures are suffering extensive erosion. The new phase of the AMP's research brought some of the latest digital technologies, including 3D laser scanning, digital photography and GPS survey equipment, to the desert cities of Merv to conduct a high definition documentation (HDD) and digital preservation project. The project served to create a point-in-time record for some of the most at-risk structures, to create a foundation data set for future erosion monitoring within the site and to research the benefits of using HDD technologies at earthen sites around the world to change the way site managers and conservers make decisions.

Historic building information modelling (HBIM)

PurposeThe purpose of this research is to outline in detail the procedure of remote data capture using laser scanning and the subsequent processing required in order to identify a new methodology for creating full engineering drawings (orthographic and 3D models) from laser scan and image survey data for historic structures.Design/methodology/approachHistoric building information modelling (HBIM) is proposed as a new system of modelling historic structures; the HBIM process begins with remote collection of survey data using a terrestrial laser scanner combined with digital cameras. A range of software programs is then used to combine the image and scan data.FindingsMeshing of the point cloud followed by texturing from the image data creates a framework for the creation of a 3D model. Mapping of BIM objects onto the 3D surface model is the final stage in the reverse engineering process, creating full 2D and 3D models including detail behind the object's surface concerning its methods of construction and material makeup, this new process is described as HBIM.Originality/valueThe future research within this area will concentrate on three main stands. The initial strand is to attempt improve the application of geometric descriptive language to build complex parametric objects. The second stand is the development of a library of parametric based on historic data (from Vitruvius to 18th century architectural pattern books). Finally, while it is possible to plot parametric objects onto the laser scan data, there is need to identify intermediate software platforms to accelerate this stage within the HBIM framework.

Laser Scanner and Terrestrial Surveying Applied to Gravitational Deformation Monitoring of Large VLBI Telescopes’ Primary Reflector

Laser scanning surveys were performed on the primary mirror of the very long baseline interferometry (VLBI) telescopes situated at Medicina and Noto observatories, with the specific purpose of investigating (1) gravity deformation patterns of the radio telescopes’ primary reflector and (2) the magnitude and relative variations of focal length as the antennas are steered in elevation. Both instruments have Azimuth-Elevation mounts and have 32 m parabolic mirrors which were surveyed in steps of 15° spanning the 90–15° elevation range. The scanning sessions were performed from two standpoints using a GS200 Trimble-Mensi; the sampling interval was set to 2 cm at a distance of 15 m. The complete surface of the main reflector at every elevation position was obtained by merging the two separate point clouds acquired from the two standpoints; each elevation is represented by at least 1.3 millions points. The merged clouds were compared for determining relative deformation patterns and magnitude. As the elevation decreases from 90−15°, the edges of the primary mirror of both telescopes fold in by a couple of cm. A least-squares adjustment was applied to point clouds corresponding to different elevations aimed at estimating the parameters of the rotational paraboloids that better fit the experimental data. This led to estimate the focal length variations induced by the structure deformative behavior. The focal lengths of the best-fit surfaces were compared. Their largest variation is found to be 2.5 cm at Medicina, between the 90° and the 15° positions. The clouds were also used to attempt a direct computation of the incoming radio signal’s path length variation due to primary reflectors’ deformations. Finally, two Leica total stations, a TDA5005 and a TC2003, were used to perform a survey of the local ground control network and of some selected targets placed on the edge of the dish. The comparison of the distances determined with the two terrestrial surveying methods (laser scanner versus triangulation and trilateration) highlights a statistically significant scale factor of about 1.0005±0.0002, being the laser estimates smaller than those obtained with total stations. This study proves that laser scanners can be efficiently used to determine gravitational influences on large VLBI telescopes’ primary reflectors: deformation patterns are clearly and reliably depicted, focal length and incoming radio signal path variations are precisely quantified.

Multimethodological approach to investigate chamber tombs in the Sabine Necropolis at Colle del Forno (CNR, Rome, Italy)

AbstractNon‐destructive geophysical prospecting methods are increasingly used for the investigation of archaeological sites, especially where a detailed physical and geometrical reconstruction of structures is required prior to any excavation work. Often, due to the limited size and depth of an archaeological structure, it may be rather difficult to single out its position and extent because of the generally low signal‐to noise (S/N) ratio. This can be overcome by improving data acquisition and processing techniques and integrating different geophysical methods. In this work the results of a multimethodological surveys, used with the aim of detecting sharp discontinuities (boundary of cavities and fractures in the host medium) at the Archaeological Test Site of Sabine Necropolis at Research Area of National Research Council of Rome (Montelibretti, Italy) are shown. For the survey a combination of passive and active methods (magnetic, ground‐penetrating radar (GPR), and dipole–dipole geoelectric (DDG)), topographical and three‐dimensional laser scanner surveys and archaeological excavations were used to study the state of conservation of underground tombs. With all geophysical methods a high‐resolution data acquisition was adopted with the aim of reconstructing a global vision of the study area. Signal processing and amplitude time‐slice representation techniques were used for the analysis of GPR data. The bi‐dimensional cross‐correlation technique was applied to enhance the S/N ratio of the magnetic data. An example of the integration (both qualitative and quantitative) of these results is presented for a portion of the investigated area in the Sabine Necropolis at Colle del Forno (Rome, Italy). Archaeological excavations were then conducted systematically after completing the geophysical surveys and interpretations (from 2000 to 2006), which confirmed the location and shape of the individual chamber tombs with associated corridors. Copyright © 2009 John Wiley & Sons, Ltd.

Underground Structure of Mud Volcanoes in Tokamachi City, Niigata Prefecture Determined by Electromagnetic Exploration, and Geographical and Geological Surveys

In Tokamachi City, Niigata Prefecture, where Tertiary sedimentary rocks are distributed, excavation of the Mt. Nabetachiyama tunnel took a long time to complete due to the presence of a swelling mudstone zone. This swelling zone is distributed at a depth of 180m under the mud volcanoes. Geological and geographical surveys as well as electromagnetic surveys applying the Controlled Source Audio-frequency Magneto-Telluric Method (CSAMT), were carried out to clarify the geological structure under the mud volcanoes and the relationship between geographical features and the swelling zone. The laser scanner survey revealed that the geological structure around the topographic depression is intensely disturbed and the geological survey showed that the mud volcanoes and eruption points of groundwater and natural gas are located mainly along the outside edge of the geologically disturbed zone. This suggests that the area was active in the past due to the uplift and eruption of groundwater. The extremely low resistivity zone (ELR) at a depth of 400m with a diameter of 500m was detected below the geologically disturbed zone by the CSAMT survey. The ELR is estimated to correspond to a mud chamber filled with saline groundwater and mud, based on laboratory tests measuring the electrical properties of several rock samples obtained from the survey area. The low resistivity zone (LR) was also detected; it continues from the ELR to the mud volcano at the ground surface, indicating that saline groundwater, mud, and natural gas may be ascending via a concentric path to the mud volcanoes. On the basis of all the results obtained, it is interpreted that the swelling zone in the tunnel corresponds to the path of mobilized mud and saline groundwater in the fractured mudstone with abnormal pore water pressure.

Terrestrial laser scan survey and 3D TIN model construction of urban buildings in a geospatial database

A new method applying close range laser scan (Lidar) survey in capturing 3D objects was presented in this study. One linear laser source Lidar was used for the survey of the objects. This approach is particularly essential for 3D modelling of urban buildings in a geospatial database. Data calibration and merging were conducted for combing point cluster datasets surveyed from different locations and angles of one object in order to generate a 3D data model for the entire object. The point cluster data were transformed and converted into a triangulated irregular network (TIN) mesh model in a 3D geospatial database. The TIN mesh model was compressed and simplified by applying a computing script of surface variability priority parameters. The digital surface images and textures of the building object were draped onto the 3D TIN model according to their coordinate locations. This research provides a direct and fast means of capturing 3D objects on the Earth's surface in a geospatial database.

Yielding mechanism of shallow mass movements in completely decomposed Norwood Tuff: the Zigzag Sign landslide, Utah

Over the past decade, land development activities on hillsides in northern Utah have resulted in a significant increase in landslide activity throughout the region. The majority of recent landslides are shallow and they occurred on cut gentle slopes especially during spring and early summer due to snowmelt induced elevated groundwater tables. The geologic material documented at numerous landslide sites is a soft gray-green completely decomposed Norwood Tuff. The present study addresses the mechanism of a shallow landslide in completely decomposed Norwood Tuff based on field, laboratory and numerical investigations. Detailed slope surface geometry obtained from laser-scan surveys together with strength and stress–strain parameters derived from laboratory triaxial tests on undisturbed samples of completely decomposed Norwood Tuff collected from the landslide site are employed with finite-element modeling to examine the effects of ground surface deformation patterns on the yielding behavior of the slide mass. The numerical results indicate a gradual retreat of the yield zone with progressive landslide deformation, which eventually becomes concentrated within the accumulation zone of the landslide, compared to a well-developed yield zone within the entire slide mass at the onset of landslide movement. Limit equilibrium stability analyses along potential sliding surfaces of extent limited within the yield zone of the displaced slide mass produce lower safety factors than an analysis based on the original sliding surface comprising the entire slide mass.

Advanced Geostructural Survey Methods Applied to Rock Mass Characterization

The location and orientation of rock discontinuities, which are traditionally obtained from geological surveys with obvious drawbacks (safety, rock face accessibility, etc.), may also be derived from a detailed and accurate photogrammetric or laser scanning survey. Selecting from the point cloud determined on the rock face a set of points distributed on a particular discontinuity, location, dip, and dip direction can be computed from the least-squares estimate of the plane interpolating the set of points. Likewise, the normal vector to the surface may be computed from an interpolation or approximation of the surface by appropriate functions. To become a real alternative (both in terms of productivity as well as accuracy) to a traditional survey, interactive or automated software tools are necessary, to allow the efficient selection of the point sets on the discontinuities or the interpretation of the normal vector pattern. After introducing the two best technologies available today for data acquisition and their performance, the paper presents an approach, based on the random sample consensus (RANSAC) procedure, to the segmentation of the point cloud into subsets, each made of points measured on a discontinuity plane of the rock face. For each subset, the plane’s equations coefficients are first determined by robust estimation and then refined by least-squares estimation after outlier removal. The segmentation algorithm has been implemented in RockScan, a software tool developed to facilitate the interaction with the point cloud in the identification of the discontinuities; rather than using the three-dimensional (3D) data, selection of regions of interest is performed on oriented images of the rock face. Finally, application of RockScan to four different test sites is discussed and results presented. The sites differ in size (from tens to hundreds of meters), rock surface characteristics, and the technology used to produce the point cloud (in three cases photogrammetry, in the fourth laser scanning), giving the opportunity to test the methodology in different contexts. In the first and in the fourth site an extensive traditional survey has been performed, providing reference data to validate the RockScan results.

Geomorphological map of the 1944 Vesuvius lava flow (Italy)

Please click here to download the map associated with this article. The map of the 1944 lava flow shows the geomorphological characteristics of a sector of the Vesuvius volcano (Italy) covered by the products emitted during the last effusive phase. The map has been produced based on the analysis and interpretation of (a) thematic maps (slope, aspect, relative relief) derived from a high resolution (0.33 m pixel) Digital Terrain Model obtained by an Airborne Laser Scanning survey, and (b) a 1 m pixel digital colour orthophoto. Different ow structures and morphologies have been interpreted. The analytical approach proposed here can be used to characterize the smaller scale topographic/geomorphological features of volcanoes and gives constraints on the mechanism of emplacement and modelling strategies of lava flows.

Emergency response and permanent measures for large landslide dams triggered by the 2004 Mid-Niigata Prefecture Earthquake in Japan

We describe various management operations undertaken by the Japanese central government in response to sediment-related disasters caused by the Mid-Niigata Prefecture Earthquake of October 23, 2004. The operations included the implementation of emergency and permanent measures for stabilizing the landslide dam in Higashi-Takezawa district as well as policy development of a sabo (erosion and sediment control) master plan for the Imogawa River basin. The earthquake caused many landslides in the Imogawa River basin. The landslide that occurred in Higashi-Takezawa district formed a large dam that reached a height of 30 m, which imposed a risk of the water level rising high enough to overflow and cause the blockage to collapse. Therefore, sabo works were undertaken by the central government to plan and implement emergency countermeasures. The Yuzawa Sabo Office of the Ministry of Land, Infrastructure, and Transport was directly responsible for these emergency measures, which included pumping out water from the reservoir to reduce the water level and prevent the landslide dam collapsing, and constructing a temporary drainage channel in preparation for the coming snowmelt and rainy season. These emergency measures ensured the safety of the downstream area. The local headquarters established in the Yuzawa Sabo Office monitored the changing conditions in the area, and planned and implemented further preventive and recovery measures while consulting with experts. In addition, an advisory committee on the landslide dams in the Imogawa River basin was established, and ad hoc meetings were held to discuss emergency and permanent measures for stabilizing the dams and developing a sabo master plan for the Imogawa River basin. Helicopter and terrestrial monitoring took place during the snowmelt and rainy season after the earthquake. In addition, aerial photo surveys and aerial laser scanning surveys were conducted to follow up with the sediment yield and runoff processes. This monitoring contributes to the security of residents and construction workers, and to the revision of the sabo master plan.

Geometric validation of a ground-based mobile laser scanning system

This paper outlines a study, carried out on behalf of a national mapping agency, to validate laser scanned point cloud data collected by a ground-based mobile mapping system. As the need for detailed three-dimensional data about our environment continues to grow, ground-based mobile systems are likely to find an increasingly important niche in national mapping agency applications. For example, such systems potentially provide the most efficient data capture for numerical modelling and/or visualisation in support of decision making, filling a void between static terrestrial and mobile airborne laser scanning. This study sought to assess the precision and accuracy of data collected using the StreetMapper system across two test sites: a peri-urban residential housing estate with low density housing and wide streets, and a former industrial area consisting of narrow streets and tall warehouses. An estimate of system precision in both test sites was made using repeated data collection passes, indicating a measurement precision (95%) of between 0.029 m and 0.031 m had been achieved in elevation. Elevation measurement accuracy was assessed against check points collected using conventional surveying techniques at the same time as the laser scanning survey, finding RMS errors in elevation in the order of 0.03 m. Planimetric accuracy was also assessed, with results indicating an accuracy of approximately 0.10 m, although difficulties in reliably assessing planimetric accuracy were encountered. The results of this validation were compared against a theoretical error pre-analysis which was also used to show the relative components of error within the system. Finally, recommendations for future validation methodologies are outlined and possible applications of the system are briefly discussed.