Abstract
This chapter analyzes the methodological approach to the study of archaeological heritage in its architectonic consistency. More specifically, two case studies are here presented to mark how their peculiarities lead the scholar to follow different processes in order to achieve a high level of awareness. More than this, the chapter tries to comprehend to what extent common tools and strategies can be applied to dissimilar case studies in archaeological field. Recent technologies in this field have given to scholars and cultural heritage experts a new tool to preserve what still exists and to virtually reconstruct what has been destroyed.
TopIntroduction
The study of archaeological structures is, of course, heterogeneous. It is related to various factors such as the site chronology, its location and consistency. Analysis and interpretation of archaeological heritage is a painstaking activity that includes a wide range of interdisciplinary subjects and competences. This work is conducted by various types of professionals: architects, archaeologists, art historians, computer scientists, etc. precisely when a strong need is felt for sharing extensive knowledge still growing with the continuous progress and the potentialities inherent in digital systems. Nowadays, this close collaboration make possible the understanding of the key elements of archaeological heritage based on considerations extracted by taking advantages of the potentialities of technologically advanced tools. What has recently been taking shape is the all-comprehensive approach which can be adapted to comprehend archaeological artifacts on a large, medium and small scale and at the same time take into consideration all the different competences involved and optimize the results obtained through concerted efforts. Within this framework studying, analyzing and contextualizing an element or an archaeological site becomes the basis for any research. Despite of the differences related to a specific context, the methodology that leads each phase of the investigation is substantially unique. During the entire process of knowledge, architectural survey1 plays a critical role as the basis for any construction of 3D model. The significance of constructing digital models in the domain of archaeology is a well-established idea and only reinforces the theoretical bases of survey and representation, conceived as structured systems for organizing and communicating information, and as the databases for critical analysis.
Architectural survey has many purposes: to validate information coming from other sources, to furnish proof of the current status and to support the following steps of the process.
In the first case, the starting point is the documentation of the past: archival and bibliographic sources, excavation notebooks, archaeologists' notes. The only documentation of the present is therefore partially useful for the knowledge of complex realities. But not only: there are some cases in which we approach the study of realities no longer existing – because they have been destroyed or because they have been profoundly modified by subsequent interventions – in which documenting the actual configuration is, in fact, impossible.
The second step involves the documentation of existing archaeological structures and artifacts is a complex activity. It consists in collecting, interpreting and disseminating a large amount of information, which help to define a system we can use to understand our archaeological heritage.
In the first two cases, a common methodology can be applied independently from the object of the research: the integrated data acquisition together with the preliminary elaboration related to them can be considered a common ground on which the survey project is built.
Otherwise, in the third case, survey is used as a tool for conservation and restoration purposes or for virtual reconstructions and analysis. In this occasion, although the starting point is a unique methodology, the data elaboration follows different procedures strictly dependent from the consistency of the case study. At this point, two categories come out from the wild field of archaeological sites: on one hand, places and archaeological remains that have been preserved in their materiality through the years, on the other hand, the ones who didn’t.
Each of the three modalities includes methodological and practical issues that must be addressed so that the result of the process constitutes a scientifically valid datum, useful to all the subjects involved in the operations of knowledge.
Key Terms in this Chapter
Survey: Process that involves the passage from the real object to its representation, which leads to the definition of graphic or virtual models through a cultural process aimed at a critical reading of the object. It often coincides in common expressions with 3D and 2D models able to describe the object to the appropriate scale of representation.
Reflectance: A fraction of the power that a small superficial area struck by an electromagnetic wave is able to reflect (re-emit). In the case of laser scanning this value can play a predictive role in relations to the physical characteristics a given material (typology, state of preservation) of which the surface of incidence is made or composed.
Eidotype: Proportional sketch of architectural/archaeological element obtained by an euristic immediate observation. It consists of plans, elevations and sections both general and details. It is used as a first reading of the object in terms of proportion, geometry, spatial configuration and architectural characterization. It is the basis for a further surveying project to record methodologies and tools of the acquisition data process.
3d Models: A 3D element created either using discretization (survey) or virtual construction (design). It can either be material (plastic, 3D print) or immaterial (virtual model). In the latter case the 3D Model is linked to the use and characteristics of modelers, software that makes it possible to interact with an initially empty digital environment enabling the operator to build elements that step by step reproduce the model once they are assembled. Direct correspondence is thus established between physical and virtual space: each material point Pr, identified thanks to its coordinates xr, yr, zr in real space, immediately finds its virtual equivalent Pv, also identified by a univocal trio of Cartesian coordinates xv, yv, zv. 3D model is conventionally an important communicative tool to help understand the represented object.
1D Models: All the textual, numerical, and alphanumerical data, which describe the object. They allow to understand the ancient configuration of an archaeological or architectural non-existing or destroyed elements, and help to define 3D/2D models in virtual space.
Surveying: Knowledge system which includes the steps of acquisition data with the aim to obtain the maximum objectivity. The techniques for the 3D survey are linked to non-contact survey, which have the aim to return the representation of a real object in a virtual three-dimensional space. Nowadays the methods of highly specialized 3D survey, as 3D laser scanner (short and long range), are comparing with the speditive ones (as the so-called structure from motion, an image-based methodology) characterized by greater speed in the phases of acquisition and elaboration of data.
Structure From Motion/Image Matching (SfM/IM): The process allows to reconstruct a 3D point cloud of an object from a set of 2D pictures. The procedure starts with the extraction of features from 2D images. The Key point extraction (operated thanks to the Scale-invariant feature transform algorithms) is followed by an operation of dense matching (RANdom SAmple Consensus algorithm) to find correspondent points in the set of pictures. At this stage, homologues points are detected and they can be projected, thanks to a photogrammetric process, into a 3D space. The result is a 3D point cloud in which each point shares the coordinate system and has got a correspondent RGB value. The point cloud can be processed in order to obtain a surface model made with triangular faces and texturized thanks the projection of the pictures on the model itself.
Texturized Model: Model obtained with techniques based on the digital development of images, use texture mapping to define in detail the chromatic aspect and the state of conservation of the organism, making a continuous exchange between the represented object and the observer, a two-way relationship between iconic representation and virtualization of the surveyed object. Textured models are suitable for general users, since they close resemble reality, and for expert users, because the photo is linked to metric information.
2d Models: The end product of the projection and section of a 3D geometric model. They are the drawings conventionally used to represent built elements at different scales. As a result, perspectives, axonometric projections, topographic projections and orthogonal projections are 2D models. However, survey uses two kinds of 2D models: geometric 2D models and architectural 2D models. The former are characterized by the geometrization of the represented elements and indicate its morphology, the spatiality of the architectural object, the actual surveyed data and sometimes the method adopted (direct, topographic, etc.). Instead the latter provide the configuration of the elements interpreted by the surveyor and through graphic characterization express the quality of the surfaces and their state of conservation.