Applied surveying education : documenting cultural heritage in 3D in the city of Ghent (Belgium) using laser scanning and photo modelling

For several years the city of Ghent (Belgium) and the Ghent University, Department of Geography have been working together to document and measure important cultural heritage sites in 3D. The partnership enables master students in Geomatics and Surveying at the Ghent University to take part in a project driven measuring campaign. During the project, students use and compare several 3D data acquisition methods. This allows the students to implement their theoretical knowledge in the field. The used methods are analysed and critically compared by the students. Through this hands-on-training, students are encouraged to think “outside the box”. When problems occur, they are stimulated to think how these problems could have happened and most importantly how they can solve them. The documentation of these historic monuments in Ghent will be used during future renovation works and archaeological research. This paper will discuss the measurements in the Ghent City Museum (Stadsmuseum or STAM). The following methods are applied during the extensive field work: engineering surveying using total station and GNSS, photo modelling and laser scanning. The deliverables are created in a CAD or GIS environment. After successful completion of the course, students have gained a significant expertise concerning the processing of topographic data, 3D point clouds and imagery in an integrated way. This knowledge can be used after their studies to assess which equipment is most suitable for any given survey project. The final products of the photo modelling and the laser scanning process is a 3D model. Furthermore, digital elevation models and orthorectified images of the historic monument can be created. The orthorectified images are visualised and processed into high resolution orthophoto plans, in a CAD or GIS environment

Analytical Comparison of Optical Methods to Evaluate the Potential of the Photo Modelling Technique for Cultural Heritage

A comparison of commercial 3D photo modelling software applications is presented. Starting from the simple acquisition of digital images, and based on the principles of photogrammetry, photo modelling represents a user-friendly and economical way to digitally preserve and three-dimensionally reproduce cultural heritage objects. The aim of this research is to evaluate the potential offered by the technique by reviewing a range of commercial and opensource software applications and making a comparison with reference data points obtained from a structured light 3D scanner. A marble artefact was selected from the collection of the Galleria Nazionale dell’Umbria di Perugia (Italy) as a test case for the analytical comparison of these two optical techniques

Determining geometric primitives for a 3D GIS : easy as 1D, 2D, 3D?

Acquisition techniques such as photo modelling, using SfM-MVS algorithms, are being applied increasingly in several fields of research and render highly realistic and accurate 3D models. Nowadays, these 3D models are mainly deployed for documentation purposes. As these data generally encompass spatial data, the development of a 3D GIS would allow researchers to use these 3D models to their full extent. Such a GIS would allow a more elaborate analysis of these 3D models and thus support the comprehension of the objects that the features in the model represent. One of the first issues that has to be tackled in order to make the resulting 3D models compatible for implementation in a 3D GIS is the choice of a certain geometric primitive to spatially represent the input data. The chosen geometric primitive will not only influence the visualisation of the data, but also the way in which the data can be stored, exchanged, manipulated, queried and understood. Geometric primitives can be one-, two- and three-dimensional. By adding an extra dimension, the complexity of the data increases, but the user is allowed to understand the original situation more intuitively. This research paper tries to give an initial analysis of 1D, 2D and 3D primitives in the framework of the integration of SfM-MVS based 3D models in a 3D GIS

Fotomodellazione e stereofotogrammetria per la creazione di modelli stratigrafici in archeologia dell’architettura

Architectural structures are 3D volumes and their features, which are recognized in the field through archaeological investigation (stratigraphic, metric and formal data), are distributed within the three-dimensions. Stratigraphic wall analysis normally needs front elevations or photo-mosaic images to draw the boundaries between each Stratigraphic Unit (SU). The Stratigraphic 3D component is not recorded because it is not taken into account by these supporting documents. With the support of photo-modelling and stereophotogrammetry, instead, it is possible to record the perimeter and volume of each SU in 3D space and also obtain isomorphic reproductions of the detected object. These copies are high quality photo-textured models that provide a complete overview of architectural volumes and the close dimensional framework (length, depth and width) of mouldings and decorative architectural elements. Moreover, the coordinates of any point can be extracted from these models in order to obtain traditional charts (maps, sections, elevations and axonometric views, useful to understand the process of installation of building elements). The purpose of this paper is to describe different techniques capable of acquiring 3D data of wall stratigraphy in order to define new methods of documentation based on the use of photo-modelling and stereophotogrammetry. The data used for this research refer to excavated sites or high-preserved fabrics of different ages and functions such as the late medieval bell-tower of the basilica of San Severo (Classe, Ravenna), the modern tower of Monte Erno (FC) and the church of San Bartolomeo in Tipano (FC). Starting with these cases, in this article we explore some of the technical aspects of data processing like speed, measurement accuracy, information content and equipment cost

Online measurement of optical fibre geometry during manufacturing

Online measurement of diameters and concentricities of optical fibre layers, and the coating layer in particular, is one of the challenges in fibre manufacturing. Currently available instruments can measure concentricity and diameter of layers offline, and are not suitable for precise monitoring or control of the manufacturing process in real time. In this work, we use two laser beams, positioned orthogonally to illuminate the fibre from two sides, and calculate deviations from the expected geometry by analysing the scattering pattern. To measure the diffraction pattern we use two 8K linear array detectors, with the scattered light incident directly on the sensors. Each detector is capturing approximately 90 degree angular range directly behind the fibre. The two measurement channels are positioned at different heights. The scattered pattern is modelled mathematically with finite-element and Fourier-modal methods, with various diameter and concentricity deviations. The sensitivities of the changes in the scattering pattern are identified in respect to these deviations. Since calculations are computationally intensive, the sensitivities are pre-calculated in advance, and the real-time measurement is based on pattern recognition. The symmetry of the pattern is used to differentiate between diameter and concentricity variations. We performed online measurements with the prototype instrument in production conditions, and show that this method is sensitive enough to measure deviations of under 1 {\mu}m in diameter and concentricity of the coating layer.Comment: Proceedings article, SPIE conference "Fiber Lasers and Glass Photonics: Materials through Applications

Towards cost-efficient prospection and 3D visualization of underwater structures using compact ROVs

The deployment of Remotely Operated Vehicles (ROV) for underwater prospection and 3D visualization has grown significantly in civil applications for a few decades. The demand for a wide range of optical and physical parameters of underwater environments is explained by an increasing complexity of the monitoring requirements of these environments. The prospection of engineering constructions (e.g. quay walls or enclosure doors) and underwater heritage (e.g. wrecks or sunken structures) heavily relies on ROV systems. Furthermore, ROVs offer a very flexible platform to measure the chemical content of the water. The biggest bottleneck of currently available ROVs is the cost of the systems. This constrains the availability of ROVs to a limited number of companies and institutes. Fortunately, as with the recent introduction of cost-efficient Unmanned Aerial Vehicles on the consumer market, a parallel development is expected for ROVs. The ability to participate in this new field of expertise by building Do It Yourself (DIY) kits and by adapting and adding on-demand features to the platform will increase the range of this new technology. In this paper, the construction of a DIY OpenROV kit and its implementation in bathymetric research projects are elaborated. The original platform contains a modified webcam for visual underwater prospection and a Micro ElectroMechanical System (MEMS) based depth sensor, allowing relative positioning. However, the performance of the standard camera is limited and an absolute positioning system is absent. It is expected that 3D visualizations with conventional photogrammetric qualities are limited with the current system. Therefore, modifications to improve the standard platform are foreseen, allowing the development of a cost-efficient underwater platform. Preliminary results and expectations on these challenges are reported in this paper

Using 3D modelling in the Valley or Turu Alty (Siberia, Russia) for research and conservational purposes

[EN] Since 1999 the Department of Archeology and the Department of Geography of Ghent University undertake field surveys to the Altai Region in Siberia, Russia. This region is a very important archaeological heritage area in the world. Scattered throughout the region are hundreds of frozen tombs, ritual monuments and petroglyphs. Research of these relics helps to understand the life of Eurasian nomads in the 4th century BC. Even more important, due to upcoming touristic activities and climate change, the documentation of the frozen tombs is imperative. A traditional archaeological survey consists out of a basic description, a drawing, one or two pictures and the GNSS location of each monument. With support of the department of Geography several topographical maps are created based on satellite images (IKONOS, Pleiades) and measurement of Ground Control Points (GCP) on site. Furthermore, since 2012 the use of 3D realistic photo modelling is being applied to survey the monuments in higher detail. The method of photo modelling proves to be successful and cost-effective. Besides their high detail, the almost real-life virtual representation of the monuments makes these techniques less abstract than a traditional archaeological survey. During the field campaigns in the summer of 2014 and 2015 this method was implied to record hundreds of monuments in the valley of Turu Alty (Siberia, Russia). Using 3D modelling software the models are created to document the monuments and petroglyphs of the study area for research and conservational purposes.Vandenbulcke, A.; Stal, C.; Lonneville, B.; Bourgeois, J.; De Wulf, A. (2016). Using 3D modelling in the Valley or Turu Alty (Siberia, Russia) for research and conservational purposes. En 8th International congress on archaeology, computer graphics, cultural heritage and innovation. Editorial Universitat Politècnica de València. 408-411. https://doi.org/10.4995/arqueologica8.2015.3787OCS40841

The role, opportunities and challenges of 3D and geo-ICT in archaeology

Archaeology joins in the trend of three-dimensional (3D) data and geospatial information technology (geo-ICT). Currently, the spatial archaeological data acquired is 3D and mostly used to create realistic visualizations. Geographical information systems (GIS) are used for decades in archaeology. However, the integration of geo-ICT with 3D data still poses some problems. Therefore, this paper clarifies the current role of 3D, and the opportunities and challenges for 3D and geo-ICT in the domain of archaeology. The paper is concluded with a proposal to integrate both trends and tackle the outlined challenges. To provide a clear illustration of the current practices and the advantages and difficulties of 3D and geo-ICT in the specific case of archaeology, a limited case study is presented of two structures in the Altay Mountains

Helium balloons for 3D modelling : off to a flying start?

Currently, the use of unmanned aerial vehicles (UAV) as a platform for aerial photography is becoming more and more common practice for 3D photo modelling applications. However, the use of these platforms has several drawbacks. Firstly, to recharge the UAV’s batteries a nearby electricity source is needed. This might cause problems when performing research in remote areas. Secondly, a skilled operator is required to control the UAV. Thirdly, there might be legal restrictions to the use of such an aerial platform in several countries. Finally, purchasing a UAV can form a big cost when performing a small project. To address these issues, the use of helium balloons as an alternative and low cost platform for aerial photography is proposed. To assess its efficiency, effectiveness and accuracy, several case studies are elaborated. In the first case study the accuracy of a 3D model created by laser scanning is compared with a 3D model created by helium balloon imagery (Ghent, Belgium). The second case study comprises a test of the performance of the system used at the lake of Vassivière (France). Finally, the helium balloons are deployed on the archaeological site of Edzna (Mexico). Here, a comparison is made between the accuracy of 3D models generated by UAV and helium balloon imagery. In conclusion, the advantages and drawbacks of the use of helium balloons as platform for aerial photography are listed. This allows potential users to make an informed choice between this and other platforms

UAV surveying for a complete mapping and documentation of archaeological findings. The early Neolithic site of Portonovo

The huge potential of 3D digital acquisition techniques for the documentation of archaeological sites, as well as the related findings, is almost well established. In spite of the variety of available techniques, a sole documentation pipeline cannot be defined a priori because of the diversity of archaeological settings. Stratigraphic archaeological excavations, for example, require a systematic, quick and low cost 3D single-surface documentation because the nature of stratigraphic archaeology compels providing documentary evidence of any excavation phase. Only within a destructive process each single excavation cannot be identified, documented and interpreted and this implies the necessity of a re- examination of the work on field. In this context, this paper describes the methodology, carried out during the last years, to 3D document the Early Neolithic site of Portonovo (Ancona, Italy) and, in particular, its latest step consisting in a photogrammetric aerial survey by means of UAV platform. It completes the previous research delivered in the same site by means of terrestrial laser scanning and close range techniques and sets out different options for further reflection in terms of site coverage, resolution and campaign cost. With the support of a topographic network and a unique reference system, the full documentation of the site is managed in order to detail each excavation phase; besides, the final output proves how the 3D digital methodology can be completely integrated with reasonable costs during the excavation and used to interpret the archaeological context. Further contribution of this work is the comparison between several acquisition techniques (i.e. terrestrial and aerial), which could be useful as decision support system for different archaeological scenarios. The main objectives of the comparison are: i) the evaluation of 3D mapping accuracy from different data sources, ii) the definition of a standard pipeline for different archaeological needs and iii) the provision of different level of detail according to the user need