ABSTRACT:Different approaches and tools are required in Cultural Heritage Documentation to deal with the complexity of monuments and sites. The documentation process has strongly changed in the last few years, always driven by technology. Accurate documentation is closely relied to advances of technology (imaging sensors, high speed scanning, automation in recording and processing data) for the purposes of conservation works, management, appraisal, assessment of the structural condition, archiving, publication and research (Patias et al., 2008). We want to focus in this paper on the recording aspects of cultural heritage documentation, especially the generation of geometric and photorealistic 3D models for accurate reconstruction and visualization purposes. The selected approaches are based on the combination of photogrammetric dense matching and Terrestrial Laser Scanning (TLS) techniques. Both techniques have pros and cons and recent advances have changed the way of the recording approach. The choice of the best workflow relies on the site configuration, the performances of the sensors, and criteria as geometry, accuracy, resolution, georeferencing, texture, and of course processing time. TLS techniques (time of flight or phase shift systems) are widely used for recording large and complex objects and sites. Point cloud generation from images by dense stereo or multi-view matching can be used as an alternative or as a complementary method to TLS. Compared to TLS, the photogrammetric solution is a low cost one, as the acquisition system is limited to a high-performance digital camera and a few accessories only. Indeed, the stereo or multi-view matching process offers a cheap, flexible and accurate solution to get 3D point clouds. Moreover, the captured images might also be used for models texturing. Several software packages are available, whether web-based, open source or commercial. The main advantage of this photogrammetric or computer vision based technology is to get at the same time a point cloud (the resolution depends on the size of the pixel on the object), and therefore an accurate meshed object with its texture. After matching and processing steps, we can use the resulting data in much the same way as a TLS point cloud, but in addition with radiometric information for textures.

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The work described in this paper deals with denoising of fine detail in terrestrial laser scanner (TLS) data for close‐range applications. In contrast to other denoising methods described in the literature, the method described here puts the problem back into two dimensions. In the proposed method, data from each instrument station is processed by denoising the range image as a 2D function. Then, after denoising, the registration process is applied to obtain the final 3D point cloud. Two image denoising methods are tested. Wavelet analysis and a “non‐local means” (NL‐means) algorithm are applied to archaeological objects of sizes described as medium (around one cubic metre) and small (around one cubic decimetre). The rich relief of these objects proves the efficiency of the method on all kinds of surface shape. The experience shows that the NL‐means method achieves good results: the standard deviation of 2 mm in the raw data is decreased to 1 mm. Besides, NL‐means denoising requires very few parameters to be set (generally two) whilst wavelet denoising requires many. Hence, the extreme simplicity of the NL‐means method makes it much more efficient and suitable for use by non‐specialists. The method, which slightly modifies the standard production process and inherits the algorithmic complexity of the classical 2D image processing schemes, allows the range of applications of TLS to be extended to small and finely detailed objects.

Abstract. The task of semantic segmentation is an important one in the context of 3D building modelling. Indeed, developments in 3D generation techniques have rendered the point cloud ubiquitous. However pure data acquisition only captures geometric information and semantic classification remains to be performed, often manually, in order to give a tangible sense to the 3D data. Recently progress in computing power also opened the way for massive application of deep learning methods, including for semantic segmentation purposes. Although well established in the processing of 2D images, deep learning solutions remain an open question for 3D data. In this study, we aim to benefit from the vastly more developed 2D semantic segmentation by performing transfer learning on a photogrammetric orthoimage. The neural network was trained using labelled and rectified images of building façades. Another programme was then written to permit the passage between 2D orthoimage and 3D point cloud. Results show that the approach worked well and presents an alternative to help the automation process for point cloud semantic segmentation, at least in the case of photogrammetric data.

ABSTRACT:3D survey techniques applied to buildings such as photogrammetry and laser scanning produces a volume of data very important. Upon acquisition, the issue of data management greatly influences the acquisition parameters and production data. Contemporary tools usually allow acquiring data sets denser than necessary without taking a very long acquisition times. We are interested in modeling from 3D data. There is no question here of mesh from the point cloud, but to model space according to their constituent elements. Data having a high density provide a rich description of the object. The issue of simplification raises the problem of loss of means of describing the object of interest. The final model, to keep the quality of description of point clouds, must remain very close to the initial data. This constraint derives the inverse problem. It is to be faithful to the data without performing mesh. The purpose of the study must remain the goal of modeling. Assumptions used to derive simple geometric primitives, which are assembled together the simplified model. The resulting model consists of surface distance for 92% of them within 5 cm of the point cloud. The model thus created is faithful to the cloud but also the rules of construction of the building which he prefigures representation.

ABSTRACT:Archaeology is a discipline closely related to the representation of objects that are at the center of its concerns. At different times of the archaeological method, representation approach takes different forms. It takes place on the archaeological excavation, during the exploration, or in a second time in the warehouse, object after object. It occurs also in different drawing scales. The use of topographical positioning techniques has found its place for decades in the stratigraphic process. Plans and sections are thus readjusted to each other, on the excavation site. These techniques are available to the archaeologist since a long time. The most of the time, a qualified member of the team performs himself these simple topographical operations. The two issues raised in this article are: three-dimensional acquisition techniques can they, first find their place in the same way on the excavation site, and is it conceivable that it could serve to support the representation? The drawing during the excavations is a very time-consuming phase; has it still its place on site? Currently, the drawing is part of the archaeological stratigraphy method. It helps documenting the different layers, which are gradually destroyed during the exploration. Without systematic documentation, any scientific reasoning cannot be done retrospectively and the conclusions would not be any evidence. Is it possible to imagine another way to document these phases without loss compared to the drawing? Laser scanning and photogrammetry are approved as acquisition techniques. What can they bring more to what is already done for archaeologists? Archaeological practice can be seen as divided into two parts: preventive archeology and classical archeology. The first has largely adopted the techniques that provide point clouds to save valuable time on site. Everything that is not destroyed by the archaeological approach will be destroyed by the building construction that triggered the excavations. The practice of classical archeology by academics is less governed by the on-site timesaving. The excavation is also the place of the transmission of knowledge and the time spent is beneficial to students. But experimenting with the production of point clouds by archaeologists of emergency can influence the practices of archeology as a whole. An experiment is ongoing on the Saint-Hilarion Monastery site in the Gaza Strip. Each layer of a stratigraphic excavation area was documented by photogrammetry. This project was the means to transfer knowledge related to photogrammetry to allow the archaeologist to document the stratigraphic layers one after the other. Indeed it is essential that this documentation is systematic and not dependent on the availability of specialist in photogrammetry. The risks related to possible wrong practices of photogrammetry by archaeologist are identified, and solutions are proposed. Monitoring means of photogrammetric missions must be established to allow complete and usable documentation. The methods implemented are alre...

<p><strong>Abstract.</strong> In this paper will be presented the use of photogrammetry integrated to the process of representation of an archaeological site. The Khirbat al-Dūsaq site, Jordan, is an architectural complex composed by three remaining buildings with different shapes and functions. The first one is a reception building name īwān. The second one is vaulted and its function has not been determined yet. The third is a bath with all the complexity that are required for such a function (multiple rooms and sequence of spaces). The site is being excavated and there remains unknown information archaeologists want to discover and represent. This project takes places after several years of collaboration on different other archaeological sites. During these different projects, methods of acquisition, processes and drawings at different places and stages have been developed and work methods that includes the use of photogrammetry are now integrated to the archaeological practices. There is now a need by archaeologists for ortho-photos to draw precise plans. The integration of photogrammetry into the practice of archaeology on site helps also to reduce the time consumption to survey and to represent excavation activity. The data sets obtained year after year can also be used as a support for 3D reconstruction. The 3D modelling stage begins by integrating the context represented here by 3D textured mesh produced during the process of ortho-photos. The integration of photogrammetry started in 2015 by acquiring pictures from bath building. This work had to be extended to the entire complex so that it has been decided to manage it, in a proper way. In 2016, a survey network has been implemented, and complete photogrammetric data set have been produced. At this time there was a photogrammetric survey reference for all the data sets of the site. Several years of survey means that the project has to adapt to its specific context. The site life during 11 months without archaeological preoccupations signifies that it is evolving, so that in 2017, ground points had disappeared. The possibility to geo-reference future data sets imposes to integrate targets on pictures from 2016 data set. The remaining building walls on site keep their shape enough to be integrated as constant structures over the years. At first it has been decided to integrate photogrammetry technic to the representation process of the Khirbat al-Dūsaq site. It has proved, by the precision and flexibility of processes that good quality representations could be produced and the 3D documentation could be used as a support of 3D reconstruction stage also. Photogrammetric documentation, as soon as it is properly managed over the years can thus be integrated in archaeologic practices and can help to reduce time consuming stages and propose other activity support as 3D reconstruction.</p>

ABSTRACT:This paper is dedicated to the digitization of blocks and virtual anastylosis of an antique façade in Pont-Sainte-Maxence (France). In 2014 during the construction of a shopping center, the National Institute for Preventive Archaeological Research (INRAP) discovered a Gallo-Roman site from the 2 nd century AD. The most interesting part of the site for the study is a façade of 70 meters long by nearly 10 meters high. The state of the conservation of the blocks of the façade makes them exceptional due to the question raised by the collapse. Representative and symbolic blocks of this building have been selected for a virtual anastylosis study. The blocks discovered belong to different types: decorated architectural blocks, monumental statuary elements and details of very fine decorations. The digital reproduction of the façade will facilitate the formulation of hypothesis for the collapse of the structure. The Photogrammetry and Geomatics Group from INSA Strasbourg is in charge of the digitization, the anastylosis and the development of exploratory methods for understanding the ruin of the façade. To develop the three-dimensional model of the facade, approximately 70 blocks of various dimensions were chosen by the archaeologists. The choice of the digitization technique is made according to the following pragmatic criterion: the movable objects are acquired with a scan-arm or a hand-held scanner in the laboratory and the largest blocks are recorded by photogrammetry at the repository near Paris. The expected types of deliverables are multiple: very accurate 3D models with the most faithful representation to document the objects in the best way and with optimized size model allowing easy handling during anastylosis tests. The visual aspect of the models is also a very important issue. Indeed, textures from photos are an excellent way to bring about the realism of the virtual model, but fine details of the object are sometimes blurred by the uniformity of the color of the original material. Acquisition by hand-held scanner does not provide the textures (they must be acquired according to a complementary process). The data types are therefore different depending on the acquisition. The type of rendering of the models depends therefore on precise choices to be defined optimally. After the acquisition, hypothesis for the construction of the façade must be validated and / or adapted by the anastylosis of the digitized blocks. Different cases must be taken into account. First, the reconstruction of broken blocks is done by adjusting the recovered fragments. If all the fragments discovered are close to the initial shape of the block, the process is assimilated to a puzzle of complex surfaces. If the fragments have no contact but are an integral part of the block, the proportion of hypotheses in relation to the contact pieces is changed. And finally, if the blocks are to be assembled together by superposition and thanks to a common plan, as assumed during the construction, the restitution could be based on the posi...