A. Wulf

In this paper, the accuracy of 3D models of both laser scanning and photogrammetry is discussed for terrestrial applications. The models constructed by photogrammetry are based on digital stereoscopic restitution and structure from motion. These models, and the models generated by processing laser scanning data, are statistically compared with topographic measurements by a total station. The textquoteleft Sint-Baafstextquoteright Abbey (Ghent, Belgium) is used as a test case in this paper. This historic site contains a series of buildings and ruins, and from these objects, a number of exterior walls are selected for virtual 3D reconstruction. Firstly, the outlines and characteristic points of these walls are measured by a total station. Secondly, a series of extra targets are measured with total station as well, in order to correctly orientate and register multiple point sets from the terrestrial laser scanner. Based on previous research in comparable projects, the angular resolutio...

ABSTRACT In this paper, a short discussion is presented on some important considerations of spatial data fusion. The discussion is motivated by the frequent lack of prescient project preparation and the possible additional costs and delays that are caused by this absence. Especially when multi-source modelling is involved in a spatial context, the definition of the user requirements, the modelling purpose and the possible data specifications are indispensable. These definitions have to be clarified even before the data acquisition takes place and they determine the development of the processing workflow. After the data acquisition, two other important phases in the modelling process are the evaluation of the conformity of the data model and the data validation. These phases are obviously linked with the predefined requirements. The importance of these phases are emphasized and motivated in this paper.

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Precise positioning with satellite based navigation systems necessitates the use of differential techniques. For differential positioning over very large areas, data on each of the individual error components (eg orbital errors, satellite clock errors) is required. Wide-area augmentation ...

For a correct georeferenced orthophoto, there is a need for a correct positioning of a certain amount of ground control points (GCP's). During the fieldwork in Altai, we tested several GPS devices. It appears that C&C C-Nav, a dual frequency, geodetic grade, GPS receiver, is a ...

ABSTRACT Breakwaters are constructed to protect seaport facilities against the destructive power of waves. A specific methodology, combining topographic and close range photogrammetric techniques, has been developed by Ghent University to perform the monitoring of the moulded concrete blocks of the breakwaters at the harbour of Zeebrugge. The focus of the developed methodology is the optimisation of the geometric accuracy of the different steps within the semi-automated process. To check the accuracy of the process, new digital terrain models of several portions of the breakwater were computed based on independent photogrammetric strips. The differences between the models can also be used to determine tolerances in position for blocks categorized as non-displaced.

The last four decades, worldwide, the landscape rapidly evolved in both a physical and anthropogenic sense. Here, the Nile valley is used as a prime example of how human impact has influenced the physical environment of large river systems. Due to its rich heritage, the cultural and environmental history of the Nile valley has already tremendously been studied. Studies focusing on the cultural history of the Nile valley are mostly field based and pinpointed towards specific target sites. These sites however were implanted in the regional landscape, and as such, information on these sites and their regional landscape are of equal importance. Digital surface models (DSMs), extracted from very high resolution stereoscopic satellite images, are a perfect tool to gain knowledge on this regional landscape aspect. Because of their stereo capability and high spatial resolution of 1.8 m, Corona Stereo couples and thus the derived DSMs are a major source for landscape analysis. In this paper several DSMs created from different Corona stereo couples dating to the early seventies are presented and discussed. The main focus is on the location of the palaeo Nile channels and it’s relation to the surrounding alluvial landscape in the area of Dayr al-Barsha, Middle Egypt. A DSM created from 2009 Worldview-1 stereo images is used as a reference and indicates the current state of the landscape. The combination of the enhanced digital terrain extraction (eATE) module of Erdas Imagine® with ground control points collected in the field and calculated from the 2009 DSM provides accurate DSMs, By comparing the Corona DSMs with the Worldview DSM, it was possible to make a risk assessment of the natural environment and urban development for cultural preservation. This comparison provides information on the complementarities and additive value of different data for archaeological investigation. As a consequence of different missions during the ’70s and frequent coverage of the area of Dayr al-Barsha, different stereo couples were processed. By combining and comparing the generated surface models the representation of the landscape is more accurate as well as the location of the palaeo river beds.

High-resolution Digital Elevation Models (DEMs) have proven to be very useful when analyzing geomorphological processes and their relationship with environmental controls. However, multi-temporal DEMs, which are required when volumetric changes need to be quantified, are often not available or expensive to produce. Recently, imagebased 3D modelling has been introduced as a methodology to produce high-resolution DEMs of both small and large landforms of any kind. As it is a rather cheap, flexible and rapid method, it is gaining importance in various geomorphological research areas, such as the study of natural hazards. Input data for the creation of DEMs are multiple overlapping photographs, taken with a normal camera. These can be photographs taken from a ground perspective, or taken from cameras mounted on Unmanned Aerial Vehicles (UAVs). In this study, we present two examples from gully erosion studies: (i) quantification of bank gully erosion from terrestrial photography (Bertem, Central Belgium; Frankl et al., 2014), and (ii) quantification of ephemeral gully erosion from low-altitude aerial photography (Hallines, Northern France). Processing the photographs was done from Structure from Motion – Multi-View Stereo workflows, integrated in various software such as PhotoScan used here. The accuracy of the obtained DEMs is at mm to cm-level. With the erosion features represented in 3D, erosion processes such as undercutting or soil piping can be studied. The feasibility of UAV photographic surveys in geomorphological studies is also discussed.

Not only for pure topographical but also for archaeological purposes, GPS is a suitable surveying technique that permits to measure detail points with a high accuracy comparable to that obtained with a totalstation, but with a higher efficiency as there is no ...

ABSTRACT In 1990 a 4-year curriculum degree of "Licence in Geography option Land Surveying" was introduced at two Belgian academic universities: both at the "Université De Liège" and at the "Universiteit Gent" ("Ghent University"). Due to the BAMA revolution (2005), these degrees have been converted in Belgium into a 5-year curriculum finalised into an academic "Master in Geomatics and Surveying" (Universiteit Gent) or a "Master in Geography, option Geomatics and Geometrology" (Université de Liège). The academic bachelor degrees that give direct access to the Master curriculum, so without additional compulsory courses, are the "Bachelor in Geography" (Université de Liège) and the "Bachelor in Geography and Geomatics, Main subject: Surveying" (Universiteit Gent). At academic universities in Belgium, the geomatics/surveying is related to geographical sciences and affiliated to the Faculties of Sciences. On the contrary, University Colleges (also called Technical Universities) offer mostly professional Bachelor degrees and some academic Bachelor and Master degrees, while Universities only offer academic degrees. Typically at University Colleges, the studies in Surveying don't exist as an independent type of education. They are seen as a continuation of the academic Bachelor in Applied Engineering sciences in Construction option Surveying (Master in Applied Engineering Sciences in Land Surveying - the degree offered at University Colleges). After 5 years, it has been decided (November 2010) to reformthe programs, based on the experience with the former ones. This article will give - and comment on – the experiences with the old program and the changes made in November 2010 to form a new and better “Master in Geomatics and Surveying” program. Also the different trajectories a student can follow to obtain this type of master degree will be explained.

Abstract Mountain permafrost modelling in remote, continental mountain ranges (eg Russian Altai Mountains) holds several difficulties due to the limitations these environments pose. The lack of meteorological input data and impossibilities for BTS-validations (Bottom ...

... Record Details. Record ID, 163392. Record Type, journalArticle. Author, Alain De Wulf [801000618736] - Ghent University Alain.DeWulf@UGent.be; Tom Willems [801001400901] - Ghent University; A MULS; Marijke Brondeel [801000962579] - Ghent University. ...

Terrestrial high resolution laser scanning is increasingly being used for geodetic deformation measurements of civil technical constructions, ie newly built tunnels. This paper deals with the error values during processing of a measured tunnel section and the final determination of the deformations of this tunnel section based on 3D laser scan point clouds.

ABSTRACT: This article will discuss a technique to convert raw or filtered laserscan-data to rasterized terrain or elevation models, by using ESRI's ArcGIS and Python. This programming language is supported since ArcGIS 9 and makes it possible to use the ArcGIS 'geo-processor' ( ...

ABSTRACT The department of Geography of Ghent University (Faculty of Sciences) acts as an important partner in a great number of archaeological projects. Each research group of the department is active in its own field of investigation and they work separately or together in many archaeological projects around the world. These research groups contribute to the measurement and recording of the sites, the understanding of geographical processes linked to these sites and their 2D, 3D or 4D visualizations. The Landscape Research and Physical Geography research groups contribute to the geomorphological and landscape analysis of archaeological sites. For landscape research, technologies such as remote sensing, GIS and landscape mapping are being used to make inventories, to study cultural values and landscape heritage, and to perform a historic landscape characterization, following a holistic approach. The Physical Geography research group focuses on the regional geomorphology, not only in Belgium but also in other parts of the world; the study of environmental changes and their impacts on geomorphological processes and the application of physical geography methodologies on archaeological sites. Together, both research groups contribute to the interpretation and environmental reconstruction of archaeological contexts, by performing field work and GI analyses. The archaeological related research activities of the 3D Data Acquisition group focus on spatial and terrestrial 3D data acquisition. The wide range of acquisition sensors, the study of their possible applications, the processing of the different types of 3D data and a thorough accuracy analysis are the main research activities. The remote sensing and photogrammetry research topics focus on different applications with satellite and aerial images obtained from different types of moving platforms (drones, helicopters, airplanes, satellites, etc.). A lot of these applications and projects are related to archaeology and the mapping of archaeological sites and their surroundings. For the acquisition of terrestrial data, the research group is working with various topographical and photogrammetric instruments: leveling instruments, (robotic) total stations, digital cameras for photogrammetric restitution and photo modelling, laser scanners, mobile mapping, GNSS receivers, etc. All these techniques are used for archaeological projects to provide accurate and detailed topographical maps of the area, digital terrain models, 3D models of archaeological objects or remains, orthophotos, 3D and 4D visualizations, etc. In the Cartography & GIS (CartoGIS) research group of the department, both fundamental and applied research on various aspects of cartography and geographical information science is conducted. With regard to archaeological projects, the research group is specialized in geographical information production, data infrastructure and the management of the geographical data. Moreover, the CartoGIS research group provides necessary 3D and 4D visualization tools for the geographical information and performs 3D/4D GIS modelling analyses and spatial temporal analyses for different archaeological projects. The different research groups in the Department of Geography (UGent) integrate different geomatics techniques for various archaeological sites and projects (Belgium; Calakmú l, Mexico; Urumqi, China; Titani, Greece; Eastern Islands; Egypt; Altaï Mountains; Malta among others). Besides the geomatics part, these integrated research activities also include geoarchaeological and geomorphological studies, GIS-based analyses and visualization tools.

ABSTRACT The destructive nature of archaeological excavations and the spatial character of archaeological finds make 3D models valuable contributions to the documentation of archaeological information. Laser scanning allows highly accurate 3D reconstructions, but involves considerable costs and expert knowledge. Therefore, photo modelling could be considered as a useful alternative. In this paper, we will demonstrate on the one hand the cost-efficiency and the consequent time-efficiency of the technique and on the other hand its (sub-decimeter) accuracy. Furthermore, the possibilities and advantages of motorized unmanned aerial vehicles (UAV) and helium balloons as airborne platform for image acquisition are shown. For this purpose, a case study is performed at the Mayan archaeological site of Edzna (Mexico). Using the Structure from Motion (SfM) and Multi-View Stereo (MVS) algorithm, terrestrial and aerial photographic recordings are processed into the final 3D models. For the quality assessment the photographic recordings are supplemented with topographic measurements.

The last four decades, worldwide, the landscape rapidly evolved in both a physical and anthropogenic sense. Here, the Nile valley is used as a prime example of how human impact may influence the physical environment. Due to its rich heritage, the cultural and environmental history of the Nile valley has already tremendously been studied. Studies focusing on the cultural history of the Nile valley are mostly field based and pinpointed towards specific target sites. These sites however were implanted in the regional landscape, and as such, information on these sites and their regional landscape are of equal importance. Digital surface models (DSMs), extracted from very high resolution stereoscopic satellite images, are a perfect tool to gain knowledge on this regional landscape aspect. In this study Corona images from 1970 and a Worldview-1 images (WV-1) from 2009 have been used in order to reveal not only environmental changes over the last four decades. In addition it also gets information on the natural landscape before the construction of the Aswan Dam, which was finished in 1970 blocking the famous natural Nile floods and major human impact could began. In this paper the challenges of DSM extraction from Corona and WV-1 images is discussed together with the detection of palaeo river channels and the evolution of anthropogenic features like villages all in the surroundings of Dayr-al Barsha (Middle-Egypt). The combination of the enhanced digital terrain extraction (eATE) module of Erdas Imagine and ground control points collected in the field provides accurate and high resolution DSMs. These surface models revealed potential palaeo river channels, and their presence has been confirmed by targeted geomorphological fieldwork in the region. Comparison between the Corona and the WV-1 DSM revealed that human impact on the landscape has been significant over the last four decades. All villages are grown in size and height. Even a number of new villages have been constructed over the last forty years. In the near future these models will be integrated with geomorphological an archaeological data in order to better understand the environmental as well as cultural evolution of the landscape in the region under study.

Perhaps the most classic way to represent 3D-objects, like the DTM from a hydrographical survey, on a 2D medium is by generating contour lines. The sight of an unsmoothed contour map can be too rough and is often rejected by the map users, especially when a shelving surface is being represented. However, many users object to smoothing on grounds that smoothed contours do not honour the linear character of the source data. Therefore, the application of smoothing procedures for aesthetic purposes should be in respect with the geometrical properties of the source data. A popular method to smooth contour lines consists in smoothing each contour independently of the rest. A second approach engages the distillation of contour lines from smooth surface patches. An eclectic procedure has been worked by A. Christensen out to combine the advantages and minimize the drawbacks of both approaches. Furthermore we have refined the eclectic method by inserting optimisation algorithms into the proce...

abstract This paper discusses the practical implementation of terrestrial laser scanning for ovalisation measurements of newly built concrete railway tunnels. Also an accuracy assessment is performed and then an overview of the measured deviations is given. This research is based on the ovalisation monitoring of concrete railway tunnels for the first projects of this kind in Belgium. These tunnels are measured with laser scanning during the first three months after construction. For all measurements, the concrete surface of the ...

ABSTRACT In the last few years, several tunnelling projects have been launched in order to extend the Belgian railway network. Among them is a new freight connection between the left and right bank of the River Scheldt in the Port of Antwerp, called the Liefkenshoek Rail Link. Since very few measurement results of actual tunnel lining behaviour are available, the start of the recent tunnel works has been an excellent opportunity to accompany the boring process with an experimental monitoring program. The measurement data obtained will be of importance for the validation of the theoretical models and the improvement of experience with shield tunnelling in soft soil.

Abstract The frozen tombs of the Scythian civilization, preserved for over 2000 years in the permafrost of the Russian, Mongolian, Chinese and Kazakh Altai Mountains, are a major archaeological find dating back to the 1920s. Inside the tombs lie bodies which have often ...

ABSTRACT The aim of the current study is to examine the role played by Thorikos within the Laurion silver mining area from the perspective of metallurgical activities during the Classical and Early Hellenistic periods. Because water availability directly determines the production output of metallurgical workshops, a hydrological analysis of the area is an ideal tool to enhance our understanding of this issue. On a large scale, hydrological modelling is accomplished through the analysis of runoff water accumulation; on a small scale, a water balance model is used to simulate the operated water supply system for industrial purposes, more specifically the purifying of silver ores in washeries. Also, the impact of cistern location on its effectiveness and usability for silver processing is explored. The two focus areas are the Velatouri Hill, where the site of Thorikos is located, and the Soureza Valley, which is situated in the centre of the Laurion. In each area a number of ore washing workshops were chosen to study in more detail. Through the region-wide hydrological and archaeological analysis, it could be shown that the Thorikos workshops contrast sharply with the Soureza ones. The latter relied on ephemeral streams which were consolidated and tapped by large cisterns, thus creating a water stock that was more than sufficient to bridge the dry periods of the year. The former relied on the harvesting of limited runoff during heavy rain events, which in many cases did not provide a sufficient water stock. Furthermore, water supply strategies in Thorikos were not as well-considered in comparison to Soureza. This leads to the conclusion that Thorikos could have never been the large scale processing site Soureza was and, when combined with the small-scale analysis, the site must have had a distinctively more ad hoc character.

The knowledge o f the underwater cultural heritage in the Belgian North Sea is rather lim ited. Yet th is submerged heritage form s an im portant aspect o f our cultural heritage and offers huge possibilities fo r scientific and (inter-)cultural purposes. However th is unique underwater archive is in danger due to increasing economic activities at sea, such as aggregate extraction, wind farms, dredging, fish ing, etc. This is not the only threat. Due to the com plexity o f the state structure in Belgium, a solid regulation regarding underwater cultural heritage is still lacking, notw ithstanding the awareness o f the need to take responsibility fo r th is heritage in danger at the political and adm inistrative level. The project SeArch offers solutions to these challenges via the development o f an effic ient assessment methodology and an approach towards a sustainable management policy and legal framework. This project involves a close collaboration between the fo llow ing partners...

The North Sea is a shallow sea that forms a complex physical system. The nonlinear interaction of the astronomical tides, varying wind fields and varying pressure systems requires appropriate approaches to be described accurately. An application based on the advanced numerical model Regional Ocean Modeling System (ROMS) was newly developed by the authors, tailored to simulate these hydrodynamic processes in the North Sea and the Belgian Continental Shelf, which is the area of particular interest in the present study. The purpose of this work is to develop and validate a state-of-the-art three-dimensional numerical model to form the basis of a compound operational and forecasting tool for the Belgian coastal zone. The model was validated with respect to water levels and temperature. Validation for astronomical tides was accomplished through the comparison of the principal constituents between the model results and observations at a number of tidal gauges in Belgium and other countrie...

Sediment transport is a key element in intertidal beach morphodynamics, but measurements of sediment transport are often unreliable. The aim of this study is to quantify and investigate cross-shore sediment transport and the resulting topographic changes for a tide-dominated, sandy beach. Two fortnight-long field experiments were carried out during which hydrodynamics and sediment dynamics were measured with optical and acoustic sensors, while the beach topography was surveyed with a permanent terrestrial laser scanner. Suspended sediment was generally well-mixed and currents were largest at approximately 1.5 m above the bed, which resulted in a peak in sediment transport at 1/3 of the high tide level. The mean transport direction was onshore during calm conditions (wave height <0.6 m) thanks to tidal currents and offshore during energetic conditions due to undertow. Oscillatory transport was always onshore because of wave asymmetry but it was subordinate to mean transport. The i...

Floods can cause damage to transportation and energy infrastructure, disrupt the delivery of services, and take a toll on public health, sometimes even causing significant loss of life. Although scientists widely stress the compelling need for resilience against extreme events under a changing climate, tools for dealing with expected hazards lag behind. Not only does the socio-economic, ecologic and cultural impact of floods need to be considered, but the potential disruption of a society with regard to priority adaptation guidelines, measures, and policy recommendations need to be considered as well. The main downfall of current impact assessment tools is the raster approach that cannot effectively handle multiple metadata of vital infrastructures, crucial buildings, and vulnerable land use (among other challenges). We have developed a powerful cross-platform flood impact assessment tool (FLIAT) that uses a vector approach linked to a relational database using open source program l...