In this paper, the accuracy of 3D models of both laser scanning and photogrammetry is discussed f... more 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 spati... more 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.
Disruption of library services 07/11-30/11 All library services will move to a new datacenter dur... more Disruption of library services 07/11-30/11 All library services will move to a new datacenter during the month of November. During this move many library services will be disturbed. Read more information on our library homepage. Sorry for any inconveniences.
Precise positioning with satellite based navigation systems necessitates the use of differential ... more 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 am... more 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 ... more 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 anthropoge... more 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 geom... more 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... more 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 Surveyi... more 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 M... more 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 ...
In this paper, the accuracy of 3D models of both laser scanning and photogrammetry is discussed f... more 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 spati... more 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.
Disruption of library services 07/11-30/11 All library services will move to a new datacenter dur... more Disruption of library services 07/11-30/11 All library services will move to a new datacenter during the month of November. During this move many library services will be disturbed. Read more information on our library homepage. Sorry for any inconveniences.
Precise positioning with satellite based navigation systems necessitates the use of differential ... more 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 am... more 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 ... more 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 anthropoge... more 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 geom... more 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... more 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 Surveyi... more 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 M... more 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 ...
Mapping and monitoring coastal areas is an important aspect of the documentation of marine dynami... more Mapping and monitoring coastal areas is an important aspect of the documentation of marine dynamics and the assessment of flooding risks. Airborne laser scanning is frequently used for this purpose, but next to this classic mapping technique, Kite Aerial Photogrammetry (KAP) is a promising alternative. In this research contribution, it is demonstrated that KAP can be used to create digital surface models in a fast and accurate manner to map and monitor sand dunes and particular areas of interest situated directly along the coastline. A case study was performed at the beach of Raversijde in Ostend, Belgium. The resulting models can be used after a storm surge, to assess the need of beach nourishment, to evaluate coastal erosion or when new constructions need to be placed along the coastline. The principle of KAP is similar to that of conventional airborne campaigns. An important factor are the weather conditions. The kite system can be used in conditions from 2 (light breeze) to 5 (fresh breeze) on the Beaufort scale. This in contrast to the use of UAVs, which need to be operated in windless conditions. The procedure involves the kite operator walking around on the beach, on which ground control points (GCPs) have been placed as black-and-white targets. To achieve the best positional accuracy, GCPs are surveyed with a total station. The kite has a working altitude of 10 to 20 meters above ground level. The kite carries a shock- and waterproof, non-metric camera of 12.1 megapixel. This camera makes it possible to acquire images with a ground resolution of less than 5 cm. Agisoft Photoscan is used to combine the photographs into a mosaic. The aerial triangulation with camera calibration and subsequent model generation is mostly an automated process. The photomosaic is georeferenced and orthorectified using the GCPs. In one day, an area of up to 10 ha can be surveyed and processed to produce digital height maps and orthorectified images. Kite systems can be used as an addition to classic topographic surveys and aircraft-based surveys, with considerable gains in the cost of the data acquisition.
ABSTRACT The aim of the current study is to examine the role played by Thorikos within the Laurio... more 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.
Satellite photographs, such as the CORONA series, are proving valuable instruments of archaeologi... more Satellite photographs, such as the CORONA series, are proving valuable instruments of archaeological reconnaissance, especially for landscapes that are relatively unknown or unprotected. Moreover, satellite imagery can be used for detailed mapping of remote areas, so that a topographic map or Digital Elevation Model can form the background for the archaeological information. However, images seen on the photographs may not be immediately recognisable as sites, and sites on the ground may escape detection from a satellite. In a current project in south Siberia the authors test the visibility of the one against the other.
Satellite imagery, and specifically CORONA, is now of common use in archaeology. CORONA, as it pr... more Satellite imagery, and specifically CORONA, is now of common use in archaeology. CORONA, as it produces two images of the same spot (afterward and forward), allows for stereoscopic view and is a perfect tool for the production of maps, especially in remote areas, where maps are not reliable of even absent. However, in all cases until now, often, it appears that only one of both images is used and that one considers this view as a geographical correct image. This is not correct. Using the test case of fieldwork and research in the Altai Mountains, we suggest that one should use both images of the same spot. Firstly, the two images give different information (shadow, lighting, different angles). Secondly, the use of both images, after georeferencing, makes it possible to produce orthophoto's and DSM's. 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 highly optimised equipment for the production of GCP's, and can be used for all types of satellite images. Common hand-held Garmin 12XL and Motorola Oncore VP hand-held GPS receivers are suitable for the localisation of archaeological sites and objects, on the condition of extensive post-processing using network solutions. These devices can also be used for CORONA as well as for other satellite images, with a resolution up to 2-4 m.
To analyse, interpret and manage our cultural heritage it is important to have an accurate and re... more To analyse, interpret and manage our cultural heritage it is important to have an accurate and realistic representation of it. Documenting this heritage involves geographic techniques such as photogrammetry, for which a lot of rather expensive and extensive platforms are already in use. However, a microdrone, a recently developed unmanned aerial vehicle platform is a cheaper and easy to handle tool. To test the very limits of the microdrone and its accompanying data-acquisition and data-processing software, we collected data from a remote area in Tuekta, in the Russian Altay Mountains. This paper presents the challenges faced during the whole photogrammetric procedure from planning the flights to producing the final deliverables. Microdrones are subject to weather conditions and site location which affect both the quality of photos and therefore the whole processing procedure. Therefore, once the conditions/restrictions had been identified and taken into account, it was possible to develop good photos. Such photos made it possible to produce accurate final products, like digital elevation models and orthophotos. These accurate deliverables prove the usefulness of such microdrones for documenting heritage at a desolate and difficult site as well as their usability for documenting the majority of our cultural and archaeological heritage. In future, it would be interesting to test a new, bigger and more stable microdrone. Together with software improvements, the whole photogrammetric process should become faster and easier.
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Papers by A. Wulf